Weather is one of the most limiting factors in producing cole crops. However, all cole crops are well-suited to Minnesota's growing season. The best quality is usually obtained with cool daytime temperatures of 70-80° F , plenty of sun, and moist growing conditions.
Cole crops grow well in any soil that is well-drained and moisture retentive. You can improve both heavy clay soils and lighter sandy soils by adding organic matter. Well-rotted manure or other composted material should be tilled into the soil prior to planting.
Soil Testing and Fertility
Commercial growers should regularly test the soil for macro and micro nutrient deficiencies. All cole crops are subject to calcium and boron deficiencies and all require manganese, magnesium, and molybdenum to be present in the soil: cauliflower also requires copper. Soil tests will tell you the level of macro and micro nutrient levels of your fields. in general cole crops require 120 to 150 pounds of nitrogen, 50 to 150 pounds of phosphorous, and 120 to 250 pounds of potassium per acre of field. Plant tissue analysis can be done in the growing season to determine nutrient toxicities and deficiencies within the crop. Foliar application of fertilizers could help produce a high quality crop if a deficiency is found.
For more complete information on specific nutrient recommendations refer to "Nutrient Management for Commercial Fruit and Vegetable Crops in Minnesota", by Dr. Carl Rosen.
Proper irrigation can be critical for maintaining high yields and quality. On average, cole crops need approximately one inch of water from rainfall or irrigation each week during the growing season. On most soils with adequate organic matter one irrigation per week is sufficient. Sandy soils may require water at more frequent intervals.
Variety selection is the most critical decision for profitable production. This decision is clearly dependent upon the targeted market as well as time of planting. For example, most early varieties of cauliflower have not been successful in Minnesota; only mid-season varieties have worked well. Although cole crop varieties were routinely evaluated in Minnesota during the early 1980's, limited university resources have prevented recent testing.
The best current information for Minnesota will be available from vegetable seed dealers and the annually revised publication, Midwest Variety Research Report,"(contact Dr. Dave Wildung, N. Central Expt. Station, Grand Rapids, MN).