Why Is My Cauliflower Turning Purple?

Cauliflower is a member of the Brassica family of vegetables, which thrive in the cooler temperatures of spring and fall. Cauliflower is grown for its large white head of immature flowers. The head is made up of "curds," which are clusters of the flowers. Our commonly known cauliflower is white, but even white heads have some color variation. They may also change tone due to climactic conditions and light levels. Slight purple or even pink tones indicate the vegetable should have been blanched, which is done in the garden by shielding the curds from high light.

Cauliflower requires daytime temperatures between 70 and 85 degrees Fahrenheit. The start time is important with cauliflower because the plant needs to be large enough to sustain the development of a large head. However, early planting is difficult as late season frost can kill or harm the young plant. Once mature, some varieties can tolerate brief exposures to temperatures down to 20 degrees. Early maturing and late maturing varieties are available, and the type you choose should be determined by the length of your growing season. The earliest maturing cauliflower is ready in about 60 days. In some areas gardeners can get an early harvest and then plant again in June for a fall harvest, but this is only possible where summer temperatures aren't extreme.

Transplants are the easiest way to start cauliflower. Transplants should have three to four true leaves before planting outside. They need to go in the ground two to three weeks after the date of the last expected frost. Create a planting bed that is well tilled and has generous amounts of compost incorporated. Remove competitive weeds and debris. Water the cauliflower starts several times per week to keep the soil moist but not soggy. Plant transplants 18 to 24 inches apart in rows 2 to 3 feet apart. Give the plants a half-strength starter fertilizer once a week, then increase to twice per week after the plants establish. Watch carefully for aphids, leaf hoppers and other pests and take steps as needed to combat such pests.

Long summer days and extremely hot temperatures cause cauliflower to turn purple. The exposure to sun is the culprit and you may even see leaves growing through the head. Once this happens there is nothing to be done, but you can prevent this from happening the next year. Blanching should begin when the cauliflower is about 2 inches across. Gather the largest exterior leaves and flop them over the head. You can tie the leaves or fasten them with a clip. The leaves will shield the developing curds from the sun but still allow them to grow.

Loosen the leaves over the head when the head is mature. Cauliflower is ready about seven to 12 days after the blanching process is started. Cut the main stem to harvest the head. The curd should not have obvious florets and should be fairly smooth. If you leave the cauliflower too long the texture gets ricey and individual florets are coarse. The plant will not produce another head so you can pull the cauliflower greens and compost them.