Planting, Spacing and Thinning
Planting dates vary widely in Utah depending on local climate conditions. Planting may begin in February in southern Utah (St. George) and may be as late as early-June in cooler mountain areas of northern Utah. Planting is recommended after danger of hard frost has passed. Local freeze dates can be accessed through the Utah Climate Center (climate.usurf.usu.edu).
Brassica seeds germinate well in cool soils (below 60°F) and is most rapid around 75 °F. Plants grow best when the mean daily temperatures are 60-70 °F and brassicas easily withstand night temperatures below 40 °F. Transplants can withstand temperatures below freezing for short periods provided they are well conditioned. Large broccoli or cauliflower transplants (6-8 leaves) may prematurely head out (button) if exposed to cold temperatures while cabbage may not form a head (blind) if excessively chilled. Temperatures above 85 °F significantly slows plant growth, alters head shape (more pointed) in cabbage, and decreases head/curd quality in broccoli and cauliflower. Cauliflower curds and broccoli floral buds grow unevenly (rough head appearance), discolor (yellow), and often have small leaves (bracts) growing up through the heads when exposed to high growing temperatures (see other production problems on pg. 34).
Plant and row spacings vary with cultivar grown, plant growth habit, available equipment, irrigation approach, and market requirements. The following spacings are common and only provided as recommendations:
Brassica Row Spacing
|Crop||Between Rows (ft.)||Within Rows (in.)||Plants/acre|
|Cabbage, Broccoli, Cauliflower||1.5-2.5||8-24||8,700-40,000|
|Kohlrabi, Mustards, Pak choi, etc.||1-2||6-15||17,500-87,000|
If direct seeding brassicas, precision plant at 0.5-1.5 lbs. seed per acre and place seed ⅓ to ½ inches deep (depending on soil moisture, time of year, and irrigation availability). Thin direct seeded plants to final spacing when they have 3-5 leaves.