When to Harvest Cauliflower:
Harvest cauliflower when heads are 6 to 8 inches (15-20 cm) in diameter but still compact and smooth.
The cauliflower head is a collection of flower buds; harvest the head while it is white and before yellow buds start to open. Cauliflower loses its flavor and texture when buds loosen.
Cauliflower is ready to harvest 70 to 90 days after sowing seed.
Plant cauliflower so it comes to harvest in a cool part of the year; the optimal growing temperatures for cauliflower are the mid 60°sF (15°+C). Plant cauliflower in early spring for harvest before summer heat or plant in late summer for fall harvest. In mild-winter regions, plant in the fall for spring harvest.
How to Harvest Cauliflower:
When heads are 2 to 3 inches (5-7 cm) in diameter—about the size of an egg, lift the outer leaves up over the head and tie them together with a piece of twine; this will blanch the head—ensuring that it is white at harvest. When heads are blanched pure white they are ready for harvest.
From the time you tie the leaves and begin the blanching process, cauliflower heads (also called “curds” and “buttons”) will be ready for harvest in about 4 days if the weather is warm and about 10 days if the weather is cool. Check heads daily to make sure they are smooth, tight, and hard. Let the heads continue to grow as long as they stay compact; an ideal head will be 6 to 8 inches (15-20 cm) across.
When curds begin to loosen, separate, and open, harvest immediately. When curds fully loosen, the head is called “ricey” and is not good for eating.
Cut heads with a sharp knife leaving about 3 inches of stem to keep the florets intact. Keep enough wrapper leaves also intact to hold the head together.
A cauliflower plant produces one head and then it is done.
How to Store Cauliflower:
Store cauliflower is a cold and moist place, 32°-40°F (0°-4°C) and 95 percent relative humidity. Cold and moist storage can be a challenge. Refrigerators provide the cold, but they also dry the air. Wrap unwashed cauliflower in a damp cloth or paper towel and put it in a perforated plastic bag in the vegetable crisper drawer of the refrigerator; this will maintain humidity.
Cauliflower will keep in the refrigerator for two to four weeks.
Stored cauliflower gives off a strong odor. As an alternative to keeping cauliflower in the refrigerator, you can store it in a cold location—at just above 32°F (0°C)—such as a root cellar, basement, shed, or garage.
Cauliflower stored below 32°F will discolor and the stem will become hollow. Cauliflower stored at low humidity levels will turn brown.
Cauliflower can be frozen shortly after harvest. Break the head into 1-inch chunks and soak them for 30 minutes in a gallon of water with a tablespoon of salt added (to kill any insects), blanch for 3 minutes, rinse, drain and then freeze.
More tips at How to Grow Cauliflower.