Problems With Broccoli Bolting

Temperature

• Broccoli grows best at temperatures between 65 and 75 degrees Fahrenheit. After experiencing a period of favorable temperatures, broccoli might bolt if temperatures drop below 50 F for 10 days or longer. The larger the plant, the more likely it is to bolt when temperatures drop. Broccoli plants also bolt when temperatures get too high before the heads are harvested. In areas where hot weather comes early in the season, choose varieties that mature quickly. Your local cooperative extension agent can advise you about when to plant broccoli in your area to reduce the chances of bolting.

Slow Growth

• Broccoli needs to grow at a steady pace. Plants that grow too fast or too slow are likely to bolt. Lack of nitrogen in the soil or competition from weeds for the available nutrients slows the growth rate. Insect infestations and diseases also prevent even growth. Broccoli needs at least 1 inch of water per week, and an inadequate water supply slows growth. Mulching helps keep the soil evenly moist and promotes steady growth. It also moderates the changes in soil temperature.

Transplants

• Older transplants are more likely to bolt than young ones. Transplant broccoli into the garden when the seedlings have five leaves and stand about 5 inches tall, or start seeds directly in the garden. Plant healthy transplants that haven’t been exposed to stress factors such as high or low temperatures or inadequate light. Harden them off before planting by exposing them to gradually increasing amounts of outdoor sun.

Harvesting

• Broccoli will bolt if you delay the harvest. The harvest begins 65 to 70 days after you set out the transplants. Cut the heads with about 6 inches of stem attached when they are 3 to 6 inches across and the heads are still tight. Many varieties produce side-shoots with smaller heads after you harvest the main head. The plant continues to produce as long as you cut the side shoots regularly.