What Happens If You Plant Broccoli Too Early?

Broccoli

• Weather is often the limiting factor for successfully growing broccoli. Fall broccoli crops can be direct-seeded, but gardeners typically start with transplants in spring to make the most of the short pre-summer cool season. In cooler climates plants will produce the large, central broccoli head in spring and smaller side-shoot heads in fall. In warm climates broccoli is planted in the fall for winter and spring harvests. Broccoli needs full sun but also rich, moist and well-drained soils and average temperatures -- between 65 and 75 degrees Fahrenheit. Provide the best possible growing conditions to produce big, healthy plants before broccoli heads form; small or weak plants will produce small heads. Broccoli is a heavy feeder, so fertilize regularly.

Starting Plants

• Many gardeners and growers start with young transplants. Buy broccoli transplants, or start seed indoors in flats two or three weeks earlier than your expected planting date. Plant seeds 1/4 to 1/2 inch deep in thoroughly moistened sterile planting mix. Set flats in a warm, sunny location or provide both bottom heat and grow lights. Transplant broccoli seedlings after the last killing spring frost to stand 18 to 24 inches apart in rows 36 inches apart; in raised beds space plants 12 inches apart in all directions. Young plants should be less than 4 inches tall but feature well-formed roots when transplanted. Water transplants well and boost root growth with a high-phosphorous transplant solution. Fall crops can be sown directly in garden soil.

Spring Planting

• Transplanting young broccoli seedlings too early in spring makes them vulnerable to late-spring frost damage -- and young plants have no frost tolerance. Early-maturing varieties are particularly vulnerable. Planting too early can also cause plants to "bolt," or begin to produce yellow flowers instead of edible broccoli heads. Bolting -- premature flower development -- happens during periods of high heat. But extended chilling of plants also causes it, especially if a prolonged cold period is followed by favorable growing temperatures and then warm conditions.

Fall Planting

• In warmer climates, where broccoli is usually planted in the fall and then overwintered, bolting can also be a problem. According to the Clemson University Extension, the larger plants are when exposed to prolonged cold, the more likely it is that plants will bolt. But other stresses can cause it too, from lack of nitrogen to weeds. Prevent bolting by planting unstressed plants, watering them well and maintaining moderate, steady growth by providing enough -- but not too much -- fertilizer. It also helps to grow slow-bolting broccoli varieties and to plant at the correct time for your area.