Sow your seeds in rows 3 to 6 inches apart in fertile material at a ½ inch deep (1.5 cm) and water them thoroughly. Cover the soil with plastic wrap until the seeds have sprouted. When the seedlings appear, remove the plastic and keep the soil evenly moist. Place them on a warm, bright windowsill to expose them to enough sunlight.
THIN: Thin to 1 plant per pot when seedlings are 2″ tall.
PLANT OUT: Set plants 18 to 24 inches apart with 30 inches between rows. Cauliflower grows best as a fall crop, but can be grown in spring, too. For spring planting, sow seeds indoors 6 to 8 weeks before the last spring frost date and plant seedlings outdoors 2 to 4 weeks before the last spring frost date. For fall planting, plant a fall crop about 8 weeks before the first fall frost date but after daytime temperatures are regularly below 75°F (24°C).
TEMPERATURE: Cauliflower can be a challenge for the beginner gardeners because it requires consistently cool temperatures in the 60°Fs (15°C). Too far below that and the plant will die. Too far above it and it may prematurely “button” (form small, button-size heads) rather than forming a single, large head. For white varieties, pink heads can indicate too much sun exposure or temperature fluctuations.
WATER: Water consistently during germination and growth. Water regularly with 2 inches of water per square foot each week; even with normal rainfall, this usually requires supplemental watering. Add mulch to conserve moisture.
FEED: Soil needs to be very rich in organic matter; mix aged manure and/or compost into the bed before planting. As an alternative, apply 5-10-10 fertilizer to the planting site. Fertile soil helps to prevent heads from buttoning. For best growth, side-dress the plants with a high-nitrogen fertilizer 3 to 4 weeks after transplanting. Brown heads indicate a boron deficiency in the soil. Drench with 1 tablespoon of borax in 1 gallon of water. (Avoid getting boron on other plants.) Or provide liquid seaweed extract immediately; repeat every 2 weeks until symptoms disappear. In the future, add more compost to the soil. Purple hues can be due to stress or low soil fertility.
PROTECT: Cauliflower dislikes any interruption to its growth. Change, in the form of temperature, moisture, soil nutrition, or insects, can cause the plants to develop a head prematurely or ruin an existing one. In early spring, be ready to protect plants from frost with row covers, if necessary. Extreme cold can halt growth and/or form buttons. In summer, shade plants from the hot sun, if necessary.
BLANCHING: When the curd (the white head) is 2 to 3 inches in diameter, blanch it: Tie the outer leaves together over the head and secure with a rubber band, tape, or twine to keep light out. (This is not necessary for self-blanching or colored varieties). The plants are usually ready for harvest 7 to 12 days after blanching.
Plants are usually ready to harvest in about 50 to 100 days, depending on variety, or 7 to 12 days after blanching. When the heads are compact, white, and firm, then it is time to harvest them. Ideally, the heads will grow to 6 to 8 inches in diameter. Cut the heads off the plant with a large knife. Be sure to leave some of the leaves around the head to keep it protected. If the heads are too small, but have already started to open up, they will not improve and should be harvested immediately.