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University of Saskatchewan College of Agriculture and Bioresources Dept. of Plant Sciences
 

 
 

High Tunnel Project (Page 2)

High tunnel structureSince 1998 we have been evaluating the potential for using high tunnels to enhance productivity and profitability of producing vegetable crops in Saskatchewan. High tunnels are similar to low tunnels in design and function, except that;

  1. one high tunnel covers several rows,
  2. the high tunnels are wide enough to allow crop growth to full maturity under the tunnels and
  3. the tunnels are tall enough to allow spraying, cultivation and harvesting to occur with the tunnels intact.

Rolling up the sides and/or opening the end doors of the high tunnels provide both ventilation and access to the crop by pollinating insects.

The initial costs of materials and installation of high tunnels are considerably higher than traditional low tunnels. However, the economics of production with high tunnels may still be favourable if;

  1. they increase yields,
  2. they enhance earliness resulting in greater market access at a time when prices are at a premium,
  3. the high tunnels are durable enough to be used for several seasons, thereby amortizing the costs of materials and installation over a greater length of time.

Below is the collection of articles on high tunnel research written since 1998. The articles are available in HTML or as PDF files.

2006 Growing Season PDF
Crops evaluated in 2006 were sequentially planted romaine lettuce and peppers.

2005 Growing Season PDF
Crops evaluated in 2005 were sequentially planted romaine lettuce, broccoli, peppers, cantaloupe, strawberries, and raspberries.

2004 Growing Season PDF
Vegetable crops evaluated in 2004 were cucumber, lettuce, tomato, pepper, muskmelon (cantaloupe), and watermelon.

2003 Growing Season PDF
Vegetable crops evaluated in 2003 were cucumber, tomato, pepper, and muskmelon (cantaloupe).

2002 Growing Season PDF
Vegetable crops evaluated in 2002 were muskmelon (cantaloupe) and pepper.

2001 Growing Season PDF
Vegetable crops evaluated in 2001 were muskmelon (cantaloupe), tomato, and pepper.

2000 Growing Season PDF
Vegetable crops evaluated in 2000 were muskmelon (cantaloupe), tomato, and pepper.

1999 Growing Season PDF
Vegetable crops evaluated in 1999 were muskmelon (cantaloupe), tomato, and pepper.

1998 Growing Season PDF
Vegetable crops evaluated in 1998 were muskmelon (cantaloupe), tomato, and pepper.

Temperature Comparison PDF
Temperature observations from 1998 - 2000 have been analyzed and compared.

Powerpoint Presentation High Tunnel Technology - Taking the Next Step (3.2 MB)
The risks and benefits of high tunnels are discussed High tunnel technology is compared with low tunnels and other crop covering technology.

 


2004 Growing Season

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In 2004, we attempted to increase productivity within the limited area of each high tunnel by testing one or two varieties of a range of crops at different planting densities. The crops tested were muskmelons (cv. Earligold and Gold Express), peppers (cv. King Arthur and Summer Sweet #830), cucumbers (cv. Fanfare), watermelon (cv. Jamboree and Sangria), lettuce (cv. Green Forest and Red Ruben) and tomatoes (cv. Big Beef and Sun Leap). Performance of plants in the high tunnels was compared to the standard low-tunnel technique. Low-tunnels were constructed of Agryl P-17 crop cover over metal hoops. The low tunnels were kept in place from the time of crop establishment until early July.

Plant populations were manipulated by varying the space between rows, while keeping the spacing within the row constant. Comparable spacing were created both inside and outside the high tunnels. Similar crop management procedures were used inside and outside the high tunnel. The crops were harvested at maturity, weighed and graded. Harvesting continued until the crop was finished or the first killing frost. The date by which 50% of the crop had matured was calculated as an indicator of the rate of crop development.

 

Results

The 2004 growing seasons was exceptionally cool and cloudy. Growth, yield and quality of the warm season crops was correspondingly poor - even with the use of the crop cover and high tunnel technology. For example, none of the cantaloupes or watermelons reached market maturity prior to the first killing frost in either production system. Peppers that had matured to full red color were also rare. Early in the season, crops in the high tunnels appeared more advanced than in the low tunnels - but in most cases this failed to result in a significant yield advantage. The close plant spacing resulted in rapid utilization of all available growing space. This reduced problems with weed competition but made access to the crop difficult, particularly within the confines of the high tunnels. The first killing frost occurred in late September in the open field. Plants in the high tunnels survived through until mid-October but little in the way of yields were obtained after late September.

 

Cucumbers

  T-50 Marketable yield/m2 Avg. fruit weight (g)
Number Weight (kg)
High tunnel  
Close spacing
Aug 26 14.2 4.1 288
Normal spacing
Aug 26 16.2 4.4 271
Low tunnel  
Close spacing
Sept 1 14.0 3.8 223
Normal spacing
Aug 26 18.8 4.1 218

Close spacing = 60 cm, normal = 120 cm. In row spacing = 30 cm.

Growing in the high tunnels produced no significant yield advantage in terms of fruit yield or time of harvest for the 2004 cucumber crop. Yields in 2004 were less than 50% of previous years although crop quality was good. The between-row plant spacing also had no impact on yields or fruit size. Fruit were slightly larger inside the high tunnel than outside - this likely reflects fewer fruit set in the high tunnels due to limited activity by pollinating insects.

Lettuce

  Green Forest Red Ruben
Stand % T-50 Yield (kg/m2) Stand % T-50 Yield (kg/m2)
High tunnel 53 Aug 3 7.0 21 Aug 3 0.8
Low tunnel 100 Aug 13 10.7 56 Aug 13 4.5

A better stand of both cultivars of lettuce was obtained outside the high tunnel than inside. Although the seed rows inside the high tunnels were drip irrigated after seeding, soil moisture conditions inside the high tunnels were not as favorable for germination as outside. The warmer conditions inside the high tunnel hastened maturity of the lettuce crop but also increased grade out due to bolting. For both cultivars, yields outside the high tunnels were far better than inside. This yield difference can be attributed to differences in stand establishment and grade out due to bolting. The crop was seeded in late May and as a consequence would have been exposed to the peak of summer heat in the high tunnels. A more positive effect of the high tunnels might be expected for lettuce crops planted either earlier or later in the growing season.

Tomatoes

  Big Beef Sun Leap
Mkt. Red (kg/m2) Cull Red (kg/m2) Mature Green (kg/m2) Immature (kg/m2) Mkt. Red (kg/m2) Cull Red (kg/m2) Mature Green (kg/m2) Immature (kg/m2)
High tunnel  
Close spacing
2.5 2.0 3.8 1.8 1.8 1.6 4.2 2.2
Normal spacing
1.0 2.0 2.6 1.9 0.7 1.4 4.6 2.4
Low tunnel  
Close spacing
0.5 0.3 6.4 2.6 0.5 0.2 7.3 1.6
Normal spacing
1.6 1.7 5.7 3.2 1.0 0.9 7.9 2.8

The tomatoes grew vigorously in the high tunnels, quickly utilizing all available space irrespective of the row spacing. The dense canopy made it difficult to harvest the fruit or effectively control disease in the high tunnel. A substantial portion of the fruit in the high tunnel were consequently lost to decay. Fruit set was also poor in the high tunnels compared to the standard production method - likely due to problems with pollination. More fruit ripened to red in the high tunnels than outside, but yields of mature green fruit were much higher outside the tunnel. In the high tunnels, the close row spacing improved productivity but row spacing had little effect on yields outside the high tunnel.

Peppers

  King Arthur Summer Sweet #830
Red (kg/m2) Mature Green (kg/m2) Immature (kg/m2) Red (kg/m2) Mature Green (kg/m2) Immature (kg/m2)
High tunnel  
Close spacing
1.7 4.7 1.6 0 2.7 1.2
Normal spacing
1.9 2.8 0.8 0.2 3.4 0.4
Low tunnel  
Close spacing
0 1.9 1.9 0 0.3 1.1
Normal spacing
0.1 2.4 1.2 0 1.1 1.6

Pepper production in the high tunnels was both higher and of greater value due to enhanced maturity than with the standard production method. These results are in direct contrast to the 2003 growing season, where pepper yields inside the high tunnel were substantially lower than when standard production methods were used. This likely reflects differences in the growing season - with the high tunnels proving beneficial under the cooler conditions experienced in 2004. Row spacing had no consistent effect on productivity inside the high tunnel, but in the standard production system the wider row spacing produced the highest yields.

Cantaloupes

  Earligold Gold Express
kg/plant kg/m2 kg/plant kg/m2
High tunnel  
Close spacing
0.3 1.7 0.6 3.1
Normal spacing
1.0 2.5 1.1 2.7
Low tunnel  
Close spacing
0.3 1.5 0.8 3.7
Normal spacing
0.6 1.7 1.2 3.0

No mature cantaloup were harvested in 2004, irrespective of the production system. Yields of immature fruit were comparable for the two types of tunnel. Close spacing improved yields of immature fruit of Gold Express both inside and outside the high tunnel.

Watermelons

  Sangria Jamboree
kg/plant kg/m2 kg/plant kg/m2
High tunnel  
Close spacing
0.4 2.0 0.2 0.8
Normal spacing
1.5 3.8 0.9 2.1
Low tunnel  
Close spacing
0.2 1.0 0.6 2.0
Normal spacing
1.0 0.6 1.2 1.7

No mature watermelons were harvested in 2004, irrespective of the production system. Yields of immature fruit of cv. Sangria were higher inside the high tunnel than outside. Close spacing improved yields of both cultivars inside the high tunnel.

 

Conclusion

High tunnels have the potential to accelerate growth of vegetable crops but this does not necessarily result in earlier or higher yields. In previous years overheating has been a problem in the high tunnels. By contrast, the 2004 growing season was so cool that even when the high tunnels were managed to maximize their heat retention, long season crops like melons failed to mature. In other crops, problems with pollination limited yields in the high tunnels. Despite the cool growing conditions, lettuce also did quite poorly in the high tunnels. Production of lettuce in the high tunnels should be limited to early spring or late fall. Peppers were the only crop to benefit substantially from production in the high tunnels in 2004 This again illustrates how cool the 2004 growing season was - in more typical growing seasons high temperature stress had been a problem for peppers in the high tunnels.


2003 Growing Season

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In 2003, we attempted to increase productivity within the limited area of each high tunnel by; a) increasing the density of planting and b) by varying the temperature inside the tunnels. The crops tested were muskmelons (cv. Earligold), peppers (cv. King Arthur), cucumbers (cv. Fanfare) and tomatoes (cv. Big Beef). Performance of plants in the high tunnels was compared to the standard low-tunnel technique. Low-tunnels keep the plants covered from the time of transplanting until early July using clear perforated polyethylene (melons and cucumbers) or spun bonded polyester (peppers) covers over metal hoops. The tomatoes were not covered.

The trial was conducted in two side by side high tunnels which were operated in a similar manner except that one tunnel was kept warmer than the other from the start of fruit set in early July through to the end of the growing season. This temperature difference was achieved by varying the degree to which the sides and ends of the high tunnels were kept open both during the day and at night. In an attempt to increase productivity within the constrained space of the high tunnels, each plant in the high tunnels was allowed less space than in the standard production situation. The total growing area per plant (high tunnels versus standard) were; tomatoes - 0.3 vs 0.5 m2, cantaloup and cucumbers - 0.2 vs 0.6 m2 and peppers - 0.1 vs 0.2 m2. Otherwise, comparable production methods were used for both tunnel types. The crops were harvested twice weekly once fruit reached maturity. Fruit were counted, weighed and graded for acceptability based on local standards. Harvesting continued until the first killing frost. The date by which 50% of the fruit had matured was calculated as an indicator of the rate of crop development.

 

Results

The 2003 growing seasons was slightly warmer than normal. The closer than normal planting coupled with the warm growing conditions resulted in rapid utilization of all available growing space in the high tunnels. However, by harvest time, the canopy was too dense in the high tunnels to allow easy access to the fruit. Early in the season, crops in the high tunnels appeared more advanced than in the low tunnels - however, overcrowding and excessive temperatures in the high tunnels environment appeared to slow the onset of fruiting in all the crops tested. This effect was particularly noticeable in the warmer of the two high tunnels. The first killing frost occurred in late September in the open field. Plants in the high tunnels survived through until mid-October but little in the way of yields were obtained after late September.

 

Cucumbers

  T-50     % Marketable
Number Weight (kg) Number Weight (kg)
High tunnel - warm Aug 21 6.8 1.4 33.8 9.8 78
High tunnel - cool Aug 17 11.3 3.2 50.3 14.4 79
Low tunnel Aug 17 27.1 8.0 45.0 13.4 89

Growing in the high tunnels dramatically reduced yields/plant but increased yield/unit area relative to the standard low tunnel system. The highest yield/unit area was obtained in the high tunnels managed to stay relatively cool. The rate of crop development (T50) was delayed in the high tunnel with the warmer conditions. More fruit were culled due to abnormal shape or mouse damage in the high tunnels than in the standard production system.

Tomatoes

  T-50 Yield (kg)/plant Yield (kg)/m2
Total Red Green Total Red Green
High tunnel - warm - 5.4 1.8 1.5 18.0 6.0 4.9
High tunnel - cool - 6.4 2.5 1.3 21.5 8.4 4.4
Low tunnel - 21.1 5.7 9.2 42.2 11.4 18.4

Growing tomatoes in the high tunnels dramatically reduced both yields/plant and yields/unit area relative to using no covers at all. The tomato plants in the high tunnels produced excessive vegetation, particularly in the warmer regime, while fruit set was quite limited in both high tunnels.

Peppers

  T-50 Yield (g)/plant Yield (kg)/m2
Total Red Mature Green Total Red Mature Green
High tunnel - warm Sept 10 700 400 100 7.4 4.5 0.6
High tunnel - cool Sept 14 700 500 100 7.6 5.3 1.1
Low tunnel - 1300 500 500 9.6 4.0 3.8

Peppers plants in the high tunnels appeared somewhat chlorotic relative to the plants growing in the open. Aphids were also more of a problem in the high tunnels than in the open. Growing peppers in the high tunnels dramatically reduced yields/plant. The high tunnel operated to produce a relatively cool environment produced the highest yields/unit area of mature red fruit while the highest total fruit yields were obtained using the low tunnel system.

Cantaloupes

  T-50 Marketable yield % Marketable
g/plant kg/m2
High tunnel - warm Oct 1 300 1.7 17
High tunnel - cool - 40 0.2 3
Low tunnel Sept 23 300 2.1 16

Although the cantaloupe plants in all treatment regimes appeared healthy, fruit yields were uniformly poor. A large proportion of the fruit were either still immature by the time of the first frost, rotted or were lost to rodent damage. In the high tunnel treatments, the best cantaloupes were obtained from section of the vines that grew outside of the tunnel structure. This negative reaction to the high tunnel environment was even more pronounced in watermelons.

 

Conclusion

High tunnels have the potential to accelerate early growth of warm season crops, but this will only result in earlier or higher yields if the high tunnels are subsequently managed so that fruit set and development are also optimized. In previous trials, fruit set in the high tunnels had been a common problem, likely as a function of; a) reduced pollen movement via insects or wind and/or b) pollen sterility due to excessive temperatures. In the 2003 trial, both of these problems were mitigated to some degree by keeping the high tunnel environment as cool as possible from early July onwards. However, yields in the high tunnels were still well below those obtained with the much cheaper low tunnels (or no tunnels for the tomatoes). In previous years, the high tunnels had provided much more substantial yield benefits relative to the low tunnels. The 2003 cropping season was unusually warm - resulting in heat stress in the high tunnels and near-optimal conditions in the open field.


2002 Growing Season

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Muskmelons

High tunnel - melon trials line graphExperience with high tunnel production of melons indicates that the majority of the fruit mature within a 10 day period. Ideally the melon production would be more evenly spread through the season. One potential means for spreading out the harvest would be to sequentially plant. In 2002, one block of 3 week old transplants of the high yielding muskmelon cv. “Earligold” was planted into the high tunnel on May 13 and another block May 23. The plants within each block were spaced 60 cm apart within the row, with 60 cm between rows. The total area for each block was 15 m2. The fruit were harvested at full slip. The harvest continued until the first killing frost in late September.

The block transplanted on May 13, began to fruit about a week earlier than the late transplanted block but otherwise the fruit yield patterns for the two plantings were very similar. Both plantings ceased to produce significant numbers of fruit after the last week in August. This suggests that growing conditions at this time were no longer suited to the crop. Total production by the early planted crop was 20% greater than the later planting. Fruit size and quality were comparable in the two plantings.

 

Conclusion

Early planting in the high tunnels is desirable as it provides both early yields and an opportunity to achieve maximum yield potential. Delaying planting appears to have limited potential as a means for extending the harvest season. Melons are an indeterminant crop capable of continuing to fruit as long as growing conditions remain favorable.

Peppers

High tunnel - bell pepper line graphAlthough peppers are a tropical plant, in previous high tunnel trials the peppers had shown symptoms of heat stress. This trial evaluated several bell pepper cultivars which had performed well under standard production conditions to determine their suitability for use in the high tunnels. Six week old, greenhouse-grown seedlings of “Super Heavy Weight”, “King Arthur”, “Camelot” and “Legionnaire” bell peppers were transplanted into the high tunnels in late May. Standard management practices were utilized. The crop was once-over harvested just prior to frost in late September. Yields of mature red, mature green and immature fruit were measured.

 

Results

Early in the season, all of the cultivars appeared very vigorous. However, as the plants began to flower, they also began to show signs of heat stress. The plants became leggy and yellow and many of the flowers failed to produce fruit. Problems with heat stress were less obvious adjacent to the ventilated edges of the high tunnel or near the doors, where temperatures would have been cooler.

Total yields of the four cultivars tested were very similar, but they varied considerably in the proportion of the fruit that matured to red prior to harvest. Over 40 % of the fruit produced by King Arthur were mature red at harvest, while none of the fruit produce by Camelot had begun to change color. As red peppers are worth much more than greens, cultivars like King Arthur which combine earliness and good yields are recommended for production in the high tunnels. Until high yielding, heat resistant varieties are identified, growers will need to employ management practices that reduce heat stress in the high tunnels.


2001 Growing Season

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High tunnels trials have been compared with standard low tunnels in four years of trials (1998-2001) conducted at the Horticulture Science Field Research Station in Saskatoon and at the Canada - Saskatchewan Irrigation Development Centre (CSIDC), Outlook. The trials have focussed on production of muskmelons, peppers and tomatoes, as these are high value crops are suited to warm environments. All crops were transplanted. Plants in the standard management plots were covered from transplanting until early July by tunnels constructed of clear perforated polyethylene (melons) or spun bonded polyester (peppers) over metal hoops. The tomatoes were not covered. The crops were harvested twice weekly once fruit reached maturity. Fruit were counted, weighed and graded for acceptability based on local standards. Harvesting of the standard management plots continued until the first killing frost at which time all remaining fruit were harvested. Harvesting of the high tunnel was discontinued once cold temperatures or senescence effectively ceased fruit production. The 1999 and 2000 growing seasons were cool to normal while the 1998 and 2001 growing seasons were exceptionally warm. The first frost was 2 weeks later in 1998 and 2001 than in 1999 and 2000.

 

High Tunnel Management

At the conclusion of the fourth growing season, the cover at the Saskatoon site was still in good enough condition to be used for another year. The cover at the more exposed Outlook site had to be replaced after three years due to tearing. Daytime temperatures within the high tunnels were well above outside air temperatures but were somewhat lower than the temperatures recorded inside the standard low tunnels. Consequently, the crop under the low tunnel developed as quickly in the spring as the crop in the high tunnel. Only after the low tunnels had to be removed due to crowding did the high tunnel produce a significant growth advantage. No unusual problems with insects were observed in the high tunnel. The high tunnel only provided about 3°C of frost protection - suggesting limited potential for extension of the growing season.

 

Melons

High tunnel - melon line graph In the 1998-2000 trials, fruit had consistently matured 2-3 weeks earlier in the high tunnel than in the standard treatments. Typically all the fruit set in the high tunnel crop had ripened by the last week of August. Yields from the high tunnel were substantially greater than in the standard production regime in years where frost cut short the growing season. In 2001, a staggered planting was tested in the high tunnel to see if the harvest could be extended into September. The first planting went in on May 8, while the second planting in the high tunnel went in a month later. The standard plots were transplanted on June 4th when the risk of frost had passed. The varieties Earligold and Carole were tested.

As in previous years, virtually all of the fruit in the early planting in the high tunnel matured by the 2nd week in August, while the outside the tunnel, the crop was a month behind. The crop planted a month later in the high tunnel did produce some fruit but yields were no better than outside the high tunnel. This suggests a 4week delay between plantings in the high tunnel is excessive. Fruit flavor and sugar content were comparable for fruit produced either inside or outside the high tunnel.

Tomatoes

In previous years, the first fruit matured 2-3 weeks earlier in the high tunnel than in the standard treatment and only a small fraction of the fruit set in the standard production system matured prior to the first frost. Plants in the high tunnel were largely unaffected by frost through until October. Yields of mature fruit were consistently greater in the high tunnel than for the standard treatment, with the amount of difference increasing in years with a short growing season. In the 2001 trial several varieties were evaluated for their adaptation to production in the high tunnels. In 2001, the crop in the high tunnel was again a week earlier than the crop outside, but there was little difference in yields of either mature fruit or total production. The 2001 growing season was exceptionally warm - resulting in excellent yields outside the high tunnel. Fruit taste and overall appearance was comparable inside or outside the high tunnel. At the termination of the trial there were still substantial numbers of immature fruit on plants both inside the high tunnel and in the standard regime.

  High tunnel Standard Production
T-50 Red (kg/plant) Green (kg/plant) T-50 Red (kg/plant) Green (kg/plant)
BHN-189 Sept 11 5.1 1.1 Sept 8 4.3 3.1
BHN-190 Aug 31 3.9 0.2 Sept 7 4.6 1.3
BHN-216 Aug 31 3.6 0.8 Sept 4 4.9 1.2
Big Beef Sept 1 5.4 0.8 Sept 4 3.0 1.1
Sunbrite Sept 2 4.3 0.5 Sept 7 4.6 0.9
Average Sept 2 4.5 0.7 Sept 5 4.3 1.5

Time to fruit maturity (T-50) and yields for tomatoes in high tunnels compared to standard production.

Peppers

In 1998 and 2000 and again in 2001, the pepper plants inside the high tunnel lacked vigor throughout the season. No definitive cause of this problem could be determined, although we suspect either overwatering or heat stress. Many of the fruit matured to red in the high tunnel, while outside the high tunnel few fruit matured to red prior to fall frost. However, the quality of the fruit in the high tunnel was poor in 2001, with many off-grade due to blossom end rot and distorted shapes. Yields of marketable fruit were much higher in the standard regime than in the high tunnel for all the varieties tested. This corresponds with the findings from several of the previous years.

  High tunnel Standard Production
Red (kg/plant) Green (kg/plant) Red (kg/plant) Green (kg/plant)
King Arthur 0.08 0 0.0 0.36
Legionnaire 0 0 0.02 0.57
Sentry 0.02 0 0.07 0.51
Superset 0.03 0 0.09 0.39
Camelot X3R 0.03 0 0 0.52
Average 0.03 0 0.04 0.47

 

Conclusion

High tunnels have the potential to accelerate growth of warm season crops, resulting in higher yields in situations where the growing season is limited. Less benefit of the high tunnels is observed in heat sensitive crops or in seasons where conditions outside the high tunnel are more favorable than normal. We have observed consistent problems with crop vigor in pepper and to a lesser extent in melon in the high tunnel at the Saskatoon site. The same crops at another site (Outlook) are not as severely affected by this problem. Although the earliness of the crops generated in the high tunnels should enhance their market value, the costs of constructing the high tunnels are substantial. The economic benefit of using the high tunnels is questionable unless some means is found to improve the productivity of the crops growing in the high tunnel.


2000 Growing Season

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High tunnels trials have been compared with standard low tunnels in three years of trials (1998-2000) conducted at the Horticulture Science Field Research Station in Saskatoon and at the Canada - Saskatchewan Irrigation Development Centre (CSIDC), Outlook. The crops tested in Saskatoon were; muskmelons, peppers and tomatoes. All crops were transplanted. Plants in the standard management plots were covered from transplanting until early July by tunnels constructed of clear perforated polyethylene (melons) or spun bonded polyester (peppers) over metal hoops. The tomatoes were not covered. Air and soil temperatures were monitored inside the high tunnel, in the standard tunnels and in the open. The crops were harvested twice weekly once fruit reached maturity. Fruit were counted, weighed and graded for acceptability based on locally accepted standards. Harvesting of the standard management plots continued until the first killing frost at which time all remaining fruit were harvested. Harvesting of the high tunnel was discontinued once cold temperatures or senescence effectively ceased fruit production. The 1999 and 2000 growing seasons were much cooler than in 1998. The first frost was 2 weeks later in 1998 than in 1999 and 2000.

 

High Tunnel Management

At the conclusion of the third growing season, the cover at the Saskatoon site was still in good condition, but the cover at the more exposed Outlook site had to be replaced due to tearing. Daytime temperatures within the high tunnels were well above outside air temperatures but were somewhat lower than the temperatures recorded inside the standard low tunnels. Consequently, the crop under the low tunnel developed as quickly in the spring as the crop in the high tunnel. Only after the low tunnels had to be removed due to crowding did the high tunnel produce a significant growth advantage. No unusual problems with insects were observed although but mice thrived in the warm sheltered conditions of the high tunnel. The high tunnel only provided about 3°C of frost protection, suggesting limited potential for extension of the growing season.

Melons

Crop development was more rapid in 1998 than in 1999 and 2000, resulting in substantial differences in yields. The first fruit always matured 2-3 weeks earlier in the high tunnel than in the standard treatments. In 1998, total yields of mature fruit of cv. Earligold were 23% higher in the high tunnel than in the standard treatment. In 1999, the high tunnel out-yielded the standard tunnels by a factor of 4 fold, while in 2000 none of the fruit in the standard tunnel treatments matured before the first frost. Fruit flavor and sugar content were comparable for fruit produced either inside or outside the high tunnel.

  1998 1999 2000
Ripe total (kg/m) % Mature Average fruit wt. (kg) Ripe total (kg/m) % Mature Average fruit wt. (kg) Ripe total (kg/m) % Mature Average fruit wt. (kg)
High tunnel 32.0 98 1.66 12.6 82 1.28 8.7 90 110
Standard Production 24.3 85 1.27 2.4 35 0.76 0 0 90
LSD NS ** ** ** ** ** ** ** *

Table 1. Yield characteristics for Earligold melon grown inside the high tunnel vs standard production practices in 1998, 1999 and 2000.

Tomatoes

Flowering was first noted two weeks earlier inside the high tunnel than in the standard management regime. In all three years, the first fruit matured 2-3 weeks earlier in the high tunnel than in the standard treatment and only a small fraction of the fruit set in the standard production system matured prior to the first frost. Plants in the high tunnel were largely unaffected by frost through until October. Total yields (weight) of mature fruit of cv. Spitfire were 33% greater in the high tunnel than for the standard treatment in 1998. In 1999, yields of mature fruit in the high tunnel were 200% greater than outside, while in 2000, yields for cv Sunbrite were 50% higher in the high tunnels than outside. Fruit taste and overall appearance was comparable inside or outside the high tunnel. The incidence of fruit rot was lower inside the tunnel than outside in 1998 and 1999, but in 2000 a high percentage of the fruit in the high tunnels were graded out due to bacterial speck. At the termination of the trial there were still substantial numbers of immature fruit on plants growing inside the high tunnel. Total yields (mature + immature) were only slightly higher inside the high tunnel than in the standard management regime.

  1998 1999 2000
Ripe total (kg/m) % Mature Average fruit wt. (g) Ripe total (kg/m) % Mature Average fruit wt. (g) Ripe total (kg/m) % Mature Average fruit wt. (g)
High tunnel 23.1 68 144 11.6 63 146 14.8 52 172
Standard Production 14.8 50 186 3.8 28 106 7.9 44 195
LSD * NS * ** ** ** ** NS *

Table 2. Yield characteristics for Spitfire tomatoes grown inside the high tunnel vs standard management practices.

Peppers

In 1998 and 2000, the pepper plants inside the high tunnel lacked vigor throughout the season. No definitive cause of this problem could be determined. The first fruit turned red 2-3 weeks earlier in the high tunnel than in the standard treatment. In 1998, yields of mature red fruit for cv, Staddon’s Select were 73% greater in the high tunnel than for the standard treatment. In 1999, no fruit matured outside of the high tunnel, while yields of mature fruit inside the high tunnel were excellent. In 2000, yields inside the high tunnel were very poor. Outside the high tunnel, the crop grew normally, but few fruit matured prior to fall frost. Average fruit size and overall appearance were comparable for fruit produced either inside or outside the high tunnel. At the termination of the trial, there were still some immature fruit on the plants both inside and outside the high tunnel. With these fruit included in the total yields, the high tunnel produced a 68% yield advantage over the standard tunnel treatment.

  1998 1999 2000
Ripe total (kg/m) % Mature Average fruit wt. (g) Ripe total (kg/m) % Mature Average fruit wt. (g) Ripe total (kg/m) % Mature Average fruit wt. (g)
High tunnel 4.5 5.01 133 2.4 2.8 116 0.9 2.4 104
Standard Production 1.1 1.56 120 0.1 0.3 136 0.1 3.1 124
LSD ** ** NS ** ** NS * ** **

Table 3. Yield characteristics for Staddon’s Select peppers grown inside the high tunnel vs standard production practices in 1998, 1999 and 2000.

Economic analysis

As indicated by Table 4, the high tunnels generally produced a higher gross return/unit row length than did the standard production practices. However, the material costs for the high tunnels ($ 31.00/m of row (assuming 3 rows) or $36.50/m2)) far exceed the cost of the standard tunnels ($ 0.78/m of row or 0.39/m2 (assuming rows are 2 m apart)). As a consequence, the net returns over capital costs for the high tunnels were only marginally better than for the standard tunnels (Table 5).

  Price z 1998 ($/m) 1999 ($/m) 2000 ($/m)
Pepper High Tunnel $1.08/kg y 5.40 3.02 2.70
Standard 1.73 0.21 2.25
 
Melon High Tunnel $0.68/kg 18.22 9.65 5.16
Standard 14.48 2.85 0
 
Tomato High Tunnel $0.81/kg 16.68 12.47 11.01
Standard 11.50 3.42 3.68

Table 4. Gross returns for High Tunnel and Standard system based on wholesale prices.
z - prices are wholesale prices FOB Saskatoon for the fall marketing period.
y - Pepper prices are for red fruit

 

  1998 1999 2000 Average
Pepper 8.2 seasons 10.7 seasons   >10 seasons
Melon 8.0 seasons 4.4 seasons 7.0 seasons 6.5 seasons
Tomato 5.8 seasons 3.3 seasons 4.9 seasons 4.6 seasons

Table 5. Number of seasons before net after material cost returns for high tunnels exceeds standard low tunnels.

 

Conclusion

Bases on three years of study, the high tunnels do not provide substantial enough yield advantage to offset their much higher purchase and operating costs, if growers are selling into the wholesale market.

Options for making High Tunnels more economical

  1. Reduce capital costs - through lower cost materials and more efficient construction.
  2. Increase yields / unit area - through use of better varieties, closer spacing of rows, staking and use of agronomic practices tailored for high intensity production.
  3. Grow higher value crops - attach price premiums to produce available either earlier or later than the competition. Direct sales result in substantially better returns than marketing through the wholesale system.

1999 Growing Season

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High tunnels trials have been conducted at the Horticulture Science Field Research Station in Saskatoon and at the Saskatchewan Irrigation Development Centre (SIDC), Outlook in 1998 and 1999. The crops tested in Saskatoon were; muskmelons, peppers and tomatoes. All crops were transplanted. Plants in the standard management plots were covered from transplanting until early July by tunnels constructed by applying clear perforated polyethylene (melons) or spun bonded polyester (peppers) over metal hoops. The tomatoes were not covered. Air and soil temperatures were monitored inside the high tunnel, in the standard tunnels and in the open. The crops were harvested twice weekly once fruit reached maturity. Fruit were counted, weighed and graded for acceptability based on locally accepted standards.

Harvesting of the standard management plots continued until the first killing frost at which time all remaining fruit were harvested. Harvesting of the high tunnel was discontinued once cold temperatures or senescence effectively ceased fruit production. The 1999 growing season was much cooler than in 1998. The first frost was 2 weeks later in 1998 than in 1999.

 

High Tunnel Structure

At the conclusion of the second growing season, the structure was still in good condition with no tears or obvious deterioration of the main plastic cover.

 

Management

Air temperatures within the high tunnels were somewhat lower than the temperatures recorded inside the standard low tunnels. Consequently, the crop under the low tunnel developed as quickly in the spring as the crop in the high tunnel. Only after the low tunnels had to be removed due to crowding did the high tunnel produce a significant growth advantage. Staking the tomato plants represented an effective means of increasing planting density in the high tunnel. No problems with insects were observed in the high tunnels, but mice thrived in the warm sheltered conditions of the high tunnel. The high tunnel only provided about 3°C of frost protection, suggesting limited potential for extension of the growing season.

 

Melons

Crop development was more rapid in 1998 than in 1999, resulting in substantial differences in yields. In both years, the first fruit matured 2-3 weeks earlier in the high tunnel than in the standard treatments. In 1998, yields of mature fruit of cv. Earligold were 23% higher in the high tunnel than in the standard treatment. In 1999, the high tunnel out-yielded the standard tunnels by a factor of 4 fold. Fruit flavor and sugar content were comparable for fruit produced either inside or outside the high tunnel.

 

  1998 1999
Ripe fruit (kg/m) Total fruit (kg/m) Average fruit wt. (kg) % Mature Ripe fruit (kg/m) Total fruit (kg/m) Average fruit wt. (kg) % Mature
High tunnel 32.0 32.6 1.66 98 12.6 15.3 1.28 82
Standard Production 24.3 23.9 1.27 85 2.4 6.6 0.76 35
LSD NS NS ** ** ** ** ** **

Table 1. Yield characteristics for Earligold melon grown either inside the high tunnel vs standard production practices in 1998 and 1999.

Tomatoes

Flowering was first noted two weeks earlier inside the high tunnel than in the standard management regime. Fruit set and fruit quality were excellent inside the high tunnel. In both years, first fruit matured 2-3 weeks earlier in the high tunnel than in the standard treatment. In both years only a small fraction of the fruit set in the standard production system matured prior to the first frost. Plants in the high tunnel were largely unaffected by frost through until October. Total yields (weight) of mature fruit of cv. Spitfire were 33% greater in the high tunnel than for the standard treatment in 1998. In 1999, yields of mature fruit in the high tunnel were 200% greater than outside. Fruit taste and overall appearance was comparable inside or outside the high tunnel. The incidence of fruit rot was lower inside the tunnel than outside. At the termination of the trial there were still substantial numbers of immature fruit on plants growing inside the high tunnel. Total yields (mature + immature) were only slightly higher inside the high tunnel than in the standard management regime.

 

  1998 1999
Ripe fruit (kg/m) Total fruit (kg/m) Average fruit wt. (g) % Mature Ripe fruit (kg/m) Total fruit (kg/m) Average fruit wt. (g) % Mature
High tunnel 23.1 34.2 144 68 11.6 18.3 146 63
Standard Production 14.8 28.9 186 50 3.8 13.3 106 28
LSD 0 NS 0 NS ** 0 ** **

Table 2. Yield characteristics for Spitfire tomatoes grown inside the high tunnel vs standard management practices.

Peppers

In 1998, the pepper plants inside the high tunnel were slow growing, chlorotic and brittle throughout the season. No definitive cause of this problem could be determined. In 1999, the crop inside the high tunnel appeared more vigorous throughout the growing season. The first fruit matured 2-3 weeks earlier in the high tunnel than in the standard treatment. In 1998, yields of mature fruit for cv, Staddon’s Select were 73% greater in the high tunnel than for the standard treatment. In 1999, no fruit matured outside of the high tunnel, while yields of mature fruit inside the high tunnel were excellent. Average fruit size and overall appearance were comparable for fruit produced either inside or outside the high tunnel. At the termination of the trial, there were still some immature fruit on the plants both inside and outside the high tunnel. With these fruit included in the total yields, the high tunnel produced a 68% yield advantage over the standard tunnel treatment.

 

  1998 1999
Ripe fruit (kg/m) Total fruit (kg/m) Average fruit wt. (g) % Mature Ripe fruit (kg/m) Total fruit (kg/m) Average fruit wt. (g) % Mature
High tunnel 4.5 5.01 133 90 2.4 2.8 116 83
Standard Production 1.1 1.56 120 77 0.1 0.3 136 1
LSD ** ** NS NS ** ** NS **

Table 3. Yield characteristics for Staddon’s Select peppers grown inside the high tunnel vs standard production practices in 1998 and 1999.

 

Conclusion

The 1998 growing season was exceptionally favorable which would tend to minimize the benefits of micro-climate modification systems, such as the high tunnel. The 1999 cropping season was more representative of a “normal” summer in terms of the average temperatures and the duration of the frost-free season. Under these more “typical” conditions, the high tunnels were much more beneficial than had been observed in the previous growing season. In the 1998 season, the high tunnels had accelerated crop development but had provided little real yield advantage. In 1999, the yield advantages obtained using the high tunnels were large and consistent. In some cases, the crops grown utilizing standard plasticulture methods actually failed to produce any marketable yield prior to the first killing frost. In a “normal” Saskatchewan growing season, using the somewhat more costly high tunnels would clearly represent a lower risk and potentially more cost-effective means of producing high-value, warm season vegetable crops.


1998 Growing Season

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The trials were conducted at the Horticulture Science Field Research Station in Saskatoon and at the Saskatchewan Irrigation Development Centre (SIDC), Outlook. The crops tested in Saskatoon were; muskmelon, peppers and tomatoes. For each crop, two cultivars were grown to test for differences in responses to the high tunnel treatments. All crops were transplanted. Plants in the standard management plots were covered from transplanting until late June by tunnels constructed by applying clear perforated polyethylene (melons) or spun bonded polyester (peppers) over metal hoops. The tomatoes were not covered. Air and soil temperatures were monitored inside the high tunnels, in the standard tunnels and in the open. The crops were harvested twice weekly once fruit reached maturity. Fruit were counted, weighed and graded for acceptability based on locally accepted standards.

Harvesting of the standard management plots continued until the first killing frost (September 30) at which time all remaining fruit were harvested. Harvesting of the high tunnels was discontinued on October 26 at which time all plants inside the tunnel were dead or had effectively ceased fruit production.

 

High Tunnel Structure

The high tunnels were easily erected with minimal construction skill or tools required. At the conclusion of the growing season, the structure was in good condition with no tears or obvious deterioration of the main plastic cover.

 

Management

On cloudless days, temperatures within the high tunnels rapidly jumped to alarming levels if the sides were left down. The high tunnels only provided about 3°C of frost protection, suggesting limited potential for extension of the growing season. Any aphids or thrips introduced on the transplants thrived in the continuously warm, humid conditions of the high tunnels. In Saskatoon, three rows of crop were grown within the 14' wide high tunnel, whereas in Outlook only two rows were grown. The more dense planting in Saskatoon had the potential to increase production per unit area but there were some problems associated with the dense planting; 1) working space was minimal once the plants matured - this made harvesting difficult, 2) damage to plants by worker traffic was intensified, particularly once harvest began. Staking the plants should be tested as a potential solution to these problems.

 

Melons

The growing conditions within the high tunnels promoted very rapid vegetative growth of the melons. Flowering began 21 days earlier inside the high tunnels than in the standard regime. The first fruit matured 2-3 weeks earlier in the high tunnels than in the standard treatments (see Figure). The time required for 50% of the fruit to mature was about one week less for the high tunnel than the standard treatment (see Figure). Frost terminated harvesting of the standard treatments in early October. Plants in the high tunnels were largely unaffected by frost through until the termination of the trial in late October. However, fruit yields were minimal from late September onwards as the plants in the high tunnels had largely senesced. Total yields of mature fruit of cv. Fastbreak were 15% greater in the high tunnels than for the standard treatment, while for cv. Earligold, the yield advantage for the high tunnels was 23% (Table 1). In both cases, this difference was not statistically significant. Fruit in the high tunnels were 10-20 % larger on average than on the outside (Table 1). Fruit flavor and sugar content were comparable for fruit produced either inside or outside the high tunnels.

  Ripe Immature Total Average fruit wt. (g) % Mature
No./m Wt. (kg/m) No./m Wt. (kg/m) No./m Wt. (kg/m)
Fastbreak

High Tunnel

17.2 21.6 0.7 0.7 17.9 22.3 1.23 97

Standard Production

15.9 18.3 5.9 5.2 21.8 23.5 1.07 77
LSD
5.4 8.7 * * 5.1 8.2 ** **
 
Earligold

High Tunnel

19.4 32.0 0.6 0.6 22.7 32.6 1.66 98

Standard Production

17.8 24.3 4.7 4.5 19.7 23.9 1.27 85
LSD
8.2 11.1 * * 7.1 10.4 * 20

Table 1. Yield characteristics for two melon varieties grown either inside high tunnels or with standard production practices.

Tomatoes

Tomatoes inside the high tunnels survived -1°C outside temperatures on June 3, while all of the plants in the standard management treatment were frost damaged. Growing conditions within the high tunnels promoted very rapid vegetative growth of the tomatoes. Flowering was first noted two weeks earlier inside the high tunnel than in the standard management regime. Fruit set and fruit quality were excellent inside the high tunnels. The first fruit matured 2-3 weeks earlier in the high tunnels than in the standard treatments (see Figure). The time required for 50% of the fruit to mature was about one week less for the high tunnel than the standard treatment. Frost terminated harvesting of the standard treatments in early October. At this time, only 50% of the fruit on cv. Spitfire had matured, while for cv. Roadside Red only 18% of the fruit were still green at first frost (Table 2). Plants in the high tunnels were largely unaffected by frost through until the termination of the trial in late October. However, fruit yields were minimal from late September onwards as low outside temperatures slowed fruit maturation. Total yields (weight) of mature fruit of cv. Spitfire were 33% greater in the high tunnels than for the standard treatment (Table 2). For cv. Roadside Red, the yield advantage for the high tunnels was 23%. For Spitfire, the fruit outside the tunnel were significantly (p=0.05) larger than inside. Fruit taste and overall appearance was comparable inside or outside the high tunnels. The incidence of fruit rot was lower inside the tunnels than outside. At the termination of the trial there were still substantial numbers of immature fruit on plants growing inside the high tunnels. Total yields (mature + immature) for Spitfire were 15% higher inside the high tunnels than in the standard management regime. The high tunnels had no effect on total yields for Roadside Red.

  Ripe Immature Total Average fruit wt. (g) % Mature
No./m Wt. (kg/m) No./m Wt. (kg/m) No./m Wt. (kg/m)
Spitfire

High Tunnel

130 23.1 104 11.1 234 34.2 144 68

Standard Production

65 14.8 88 14.1 153 28.9 186 50
LSD
** * 89 9.4 ** 7.3 * 29
 
Roadside Red

High Tunnel

134 18.1 51 3.5 185 21.6 110 85

Standard Production

98 13.6 32 3.3 130 16.9 123 20
LSD
57 * 52 5.0 90 10.4 40 20

Table 2. Yield characteristics for two tomato varieties grown inside high tunnels or with standard management practices.

Peppers

In Saskatoon, peppers in the high tunnel were slow growing, chlorotic and brittle throughout the season. No definitive cause of this problem could be determined. Peppers in the standard regime were healthy as were peppers grown within high tunnels in Outlook. In Saskatoon, fruit set inside the high tunnels was substantially delayed relative to expectations. Nonetheless, the first fruit matured 2-3 weeks earlier in the high tunnels than in the standard treatments (see Figure). An unusually high proportion of the fruit in the high tunnels was graded out to either blossom end rot or sunscald. The time required for 50% of the fruit to mature was about one week less for the high tunnel than the standard treatment (see Figure). Yields of mature fruit were 73% greater in the high tunnels than for the standard treatment (Table 3). Average fruit size was 17% larger on plants grown outside the tunnels than inside, but this difference was not statistically significant. Fruit taste and overall appearance was comparable for fruit produced either inside or outside the high tunnels. At the termination of the trial, there were still some immature fruit on the plants both inside and outside the high tunnels. With these fruit included in the total yields, the high tunnels produced a 68% yield advantage.

  Ripe Immature Total Average fruit wt. (g) % Mature
No./m Wt. (kg/m) No./m Wt. (kg/m) No./m Wt. (kg/m)
High Tunnel 31.9 4.5 5.4 0.47 37.4 5.01 133 90
Standard Production 6.5 1.1 5.3 0.44 11.8 1.56 120 77
LSD
** ** 6.6 0.97 ** ** 54 24

Table 3. Yield characteristics for Staddon’s Select peppers grown inside high tunnels or with standard production practices.

Conclusion

Early yields of all crops were enhanced by the high tunnels but the impact on total yields was crop specific. Selection of better adapted cultivars (heat tolerant and higher yielding ) coupled with use of appropriate production practices (staking) should substantially improve the performance of crops grown within the high tunnels. The 1998 growing season was exceptionally favorable which would tend to minimize the benefits of micro-climate modification systems, such as the high tunnels. Construction costs for the high tunnels are substantially higher than standard practices, but the structures appear sufficiently durable to last several seasons.

University of Saskatchewan