Sequential Planting Research
Sequential planting represents a means of insuring a consistent supply of product. Changing growing conditions and pest pressures over the season can influence the relative performance of sequential plantings.
The following is a collection of articles evaluating sequential planting of spinach and lettuce. The articles are available as HTML documents and PDF files.
Quality of Sequentially Planted
Head Lettuce PDF
Growers commonly report indicate problems with quality in head lettuce. In cultivar trials conducted by the University of Saskatchewan, over 50% of the crop was commonly graded as unmarketable. Problems with poor flavor, bolting and tip burn are often attributed to excessively high temperatures. Leaf drop caused by the fungal pathogen Sclerotinia sclerotiorum is also a problem for growers relying on heavy irrigation to get the crop through a period of excessive heat.
This trial evaluated quality of head lettuce crops transplanted at differing stages of a Saskatchewan growing season. It was expected that the quality of the earliest transplanted crop would be superior to crops grown during the heat of mid-summer. The potential to use fungicides to control leaf drop was also evaluated.
The cultivars ‘El Dorado’ and ‘Lighthouse’ were selected for testing as they produced the highest yields of marketable heads in previous cultivar trials. The trial was conducted using an overhead irrigation system on the University of Saskatchewan Vegetable Research Plots. This site features a heavy clay soil and is extensively infested with Sclerotinia.
Three week old, greenhouse grown seedlings were transplanted into the field on May 17, June 14 or July 12. Half of the seedlings were treated with the fungicide Rovral (iprodione) as a root drench just prior to transplanting and again as a foliar treatment 5 days after transplanting. The fungicide treatments were timed to minimize opportunities for the Sclerotinia fungus to become established in the crop. The seedlings were spaced 25 cm apart in 4 m long rows with 75 cm between rows. The lettuce was harvested once it reached the desired head density. Heads were weighed and graded for marketability based on local market standards.
May, June and early July were exceptionally hot and dry in 2002, while from mid-July onwards conditions were considerably cooler, with significant rainfall. The two cultivars tested responded very similarly - the data for ‘El Dorado’ is presented in Table 1. The earliest planting was severely set back by hot, dry conditions at the time of transplanting. Consequently, the first planting was ready for harvest only 5 days earlier than the second planting. Problems with tip-burn and leaf drop caused by Sclerotinia combined to severely reduce marketable yields in the first two plantings. The fungicide treatments provided no control of leaf drop. Yields and quality of the third planting were excellent. Although the cool and moist growing conditions that prevailed during this period slowed crop development, they also appeared to eliminate problems with both tip-burn and leaf drop.
Production of high quality head lettuce hinges on consistent and moderate growing conditions. As growing conditions in Saskatchewan are both variable and unpredictable, production of head lettuce is clearly risky. The absence of effective means for dealing with fungal diseases of this crop further increases the production risk. Acceptable yields of high quality head lettuce can be achieved if stress resistant cultivars are planted in periods when cooler conditions will prevail. Extremely early (late April) and late (mid-August) transplanting dates might be worth considering.
Spinach is a cool season crop well suited to production in spring in Saskatchewan. However, most growers report difficulties in establishing and growing good quality spinach crops during July and August. Cool soil temperatures (5°C) promote germination of spinach but emergence is slow from these cold soils. Higher soil temperatures induce thermal dormancy in spinach seed. Bolting in spinach is triggered by long days (12-15 hours) and cold weather followed by warmer temperatures. Bolting sensitivity varies between cultivars.
This trial evaluated the performance of several cultivars of spinach sequentially planted over the course of the 2000 and 2001 growing seasons. The trials were conducted at the University of Saskatchewan Field Headquarters in Saskatoon (clay soil) and at the CSIDC in Outlook (sandy loam). The cultivars selected for trial were;
The crops were direct seeded into field plots rotovated and fertilized one week ahead of planting. The plot area was irrigated and managed according to standard recommendations for spinach. Each test consisted of 8m (2000) or 6m (2001) long rows of each cultivar replicated four times in a split plot design, with plantings as the main plots and cultivars as the sub-plots. Four plantings were tested in each season;
The crop was taken in a once over complete harvest when at least 50% of the plants were 10 cm tall or at the first sign of crop bolting. In 2001, the crop was harvested at a slightly earlier growth stage than in 2000. At harvest, each crop was evaluated for stand establishment, yields, crop quality and bolting.
In both years, stand establishment at the Saskatoon site was superior to that in Outlook. In the 2000 trial this translated into a significant yield advantage for the Saskatoon site. The heavy clay soil in Saskatoon appeared to better retain the moisture required for germination of the spinach crop. The flavor and quality of the crops were comparable at the two test sites. In the 2000 trial, the cultivar Tyee produce the best stand and the highest yields at both sites at all planting dates. In the 2001 trial, Olympia produced the best yields followed by Tyee. In both years Olympia and Tyee had good flavor and a very low incidence of bolting. Bloomdales had the highest proportion of the crop bolted in all trials.
In the 2000 trial, the first and second plantings produced a better stand and much higher yields than the third or fourth plantings. By contrast, in 2001, the third planting produced an excellent stand and the highest yields of any trial. It does not appear that the soil temperatures encountered mid-summer in Saskatchewan are high enough to trigger thermal dormancy in spinach. In both years, the second planting had the highest percentage bolting - this indicates that the daylength and temperature encountered by this planting are not favorable to holding the crop in a vegetative state. The fourth planting produced very little at either site in both years - late summer conditions were not conducive to rapid growth of the crop. In the 2000 trial, time of planting had no impact on crop flavor, but in the 2001 trial the earliest plantings were considered superior.
Yield potential for sequentially planted spinach varied somewhat with the growing season. Planting from early May through early July produced acceptable yields, although planting near the longest days of the year triggered early bolting. Tyee and Olympic appear best suited to the daylengths and temperatures encountered during the Saskatchewan growing season. None of the cultivars tested were suited to planting after mid-August.