Broccoli, cabbage, and cauliflower are members of the cabbage family. They are also referred to as cole crops. Cole crops are cool season vegetables which grow best at temperatures between 60 and 70 degrees F. When planted in spring, these crops produce good quality heads before the arrival of hot summer weather.
While cole crops are cool season vegetables, they should not be planted when temperatures are consistently below 50 degrees F. Broccoli and cauliflower plants exposed to prolonged periods (four or more days) of temperatures below 50 degrees F may form heads prematurely. This premature head development is called buttoning. Buttoning occurs when plants are exposed to stressful conditions, such as prolonged periods of cold temperatures, dry conditions, and infertile soils. Also, large plants are more likely to button than young plants. Plants that button do not form usable heads.
In central Iowa, broccoli, cabbage, and cauliflower should be planted in mid-April. Start plants indoors 5 to 6 weeks before planting outdoors or purchase young, stocky transplants at your local garden center. Harden the transplants outdoors in a protected location for a few days prior to planting.
Cole crops perform best in fertile, moist, well-drained soils. When planting these crops, space transplants 18 to 24 inches apart within the row. Rows should be approximately 30 to 36 inches apart. At transplanting, apply 1 pint of a starter fertilizer solution to each plant. A starter fertilizer solution can be prepared by placing 2 tablespoons of a complete analysis fertilizer, such as 10-10-10 or 12-12-12, in one gallon of water. Three to four weeks after transplanting, sprinkle 1 or 2 tablespoons of the complete fertilizer around each plant.
Broccoli, cabbage, and cauliflower require approximately 1 inch of water per week. Water plants once a week during dry weather. Cultivate lightly around cole crops as they have a shallow root system.
These crops can also be planted in mid-summer for a fall crop. Start the seed indoors in early July. Transplant the seedlings into the garden 5 to 6 weeks later.
Suggested broccoli, cabbage, and cauliflower varieties for Iowa include:
Arcadia, Goliath, Green Comet, Packman, and Premium Crop
Bravo, Charmant, Green Cup, Head Start, and Stonehead
Red Acre, Regal Red, and Ruby Perfection
Savoy Ace, Savoy Blue, and Savoy King
Andes, Fremont, Snow Crown, and White Sails