There is no need for alarm when cauliflower heads in your garden turn purple around the outside edge. Assuming that you aren't growing one of the deliberately purple varieties, your cauliflower is just being cauliflower, and the coloration is not caused by a disease, fungus or pest.
Why Cauliflower Turns Purple
Genetically, many cauliflowers tend toward purple, red or blue pigments. Cauliflower is a cool-weather vegetable, and when a lot of heat and sunlight hits the developing cauliflowers, they can display a purplish tinge along the edges of the heads. The edible portion of the plant is the head of flower buds, called the curd. The purple color in cauliflower is caused by the presence of anthocyanin, a harmless, water-soluble pigment in the curd. Sun exposure exaggerates its effect on the developing cauliflower head.
Ways to Prevent a Purple Tinge in Cauliflower
- Purchase a self-blanching variety developed to reduce tinting
- Schedule the development of the cauliflower for the cool months in fall
- Cover the head as it develops with surrounding leaves, a process known as blanching.
To get perfectly white cauliflower in the garden, you need to blanch the cauliflower by covering the developing head with leaves. Even if the cauliflower is already showing a tint around the edges, you should get that head of cauliflower covered up and out of the sunlight. To blanch the cauliflower, simply draw the surrounding leaves up and around the head of cauliflower. Tie the leaves with garden twine or use a rubber band to hold the leaves closed, and you won't have to worry about any further coloring of the cauliflower curds.
When to Blanch
Start checking your plants about 30 days after you transplant them into the garden. When you see a cauliflower curd that is about the size of an egg, it is time to blanch. The curd continues to grow rapidly, and you'll probably need to adjust the positioning of the leaves covering the curd as this happens.
Is Purple Cauliflower Safe to Eat?
If your cauliflower has already turned purple on the edges, don't despair. It is perfectly safe to eat it either raw or cooked, although the flavor may be subtly different from the familiar white variety. When you cook the cauliflower, the purple tinge turns gray, particularly when the cooking water is hard or has an alkaline pH. This may look unappetizing, but a bit of vinegar added to the water minimizes the color change.
Purple Cauliflower Varieties
Brightly-colored cauliflower has become increasingly popular at gourmet markets, and seeds are available for lime green, purple, and orange varieties from most of the popular garden seed companies.
In the case of these brightly-colored cauliflower varieties, there is no need to blanch, as they're meant to look that way. Bright sunlight intensifies the color of the curds.