My Brussels Sprout Plants Bolted: Reasons Why Brussels Sprouts Are Bolting

Bloting Brussel Sprouts
brussels sprouts
(Image credit: Jeanne Emmel)

You tenderly plant them, you carefully weed them, then one hot summer day you discover your brussels sprouts are bolting. It's frustrating, especially if you don't understand how to stop brussels sprouts from bolting. One thing is clear. Once they begin flowering, brussels sprouts won't produce those mini cabbage-like heads that have become so popular in roasted vegetable medleys.

Brussels Sprouts and Bolting

Bolting is a plant's natural inclination to propagate. When temperatures and daylight hours increase, annual leafy green vegetables, like lettuce, will quickly send up a stem with a flowering head at the top. When this happens, the plant puts its energy into flower and seed production, not leaf growth.

Biennials, like brussels sprouts, can bolt for slightly different reasons. These plants have a two-year life cycle. During the first year, the plant concentrates its energy on leaf production. When temperatures stay warm enough for the biennial to survive the winter, the second year is dedicated to flower and seed production.

Exposing young biennials to cold weather early in their first year can trigger these plants into thinking they survived the winter. Then, when warm temperatures arrive in the summer, these biennials think it's year number two and begin flowering. Brussels sprouts tend to bolt if planted at the wrong time of year.

How to Stop Brussels Sprouts from Bolting

First and foremost, it's essential to plant cool-season plants that are prone to bolt at the correct time of the year. If your brussels sprout plants bolted last year, try re-evaluating your planting schedule. The optimal time to plant brussels sprouts depends upon your climate and the harshness of the winter months.

  • Warm winters (Temperatures rarely dip below freezing): Sow brussels sprout seeds directly into the garden soil in late summer. Harvest time, mid to late winter.
  • Mild winters (Temperatures occasionally drop below freezing): Sow brussels sprout seeds directly into the garden soil in early to midsummer. Harvest time, mid fall to early winter.
  • Cold winters (Temperatures remain below freezing): Start brussels sprouts indoors several weeks before the last frost. Harvest time, early fall.

Unusual weather patterns and inadequate growing conditions can also contribute to leafy vegetables prematurely flowering. If you've planted at the correct time and you still find your brussels sprouts are bolting, try the following tips:

  • Apply a generous layer of mulch around your brussels sprouts. Mulch helps retain soil moisture, reduces competition from weeds, and keeps the soil temperature cooler.
  • Water brussels sprouts during dry spells. They prefer a consistently moist soil.
  • Plant brussels sprouts in tightly packed, fertile soil. Periodically apply a high nitrogen fertilizer to stimulate leaf growth.
  • Protect young seedlings and new transplants from unexpected cold snaps. Bring potted seedlings inside and cover garden transplants.

Finally, if all else fails and you still find flowering brussels sprouts in the garden, choose hybrid varieties of brussels sprouts that are slow to bolt. Many heirloom brussels sprout varieties, while great tasting, are more prone to bolting.

Laura Miller

Laura Miller has been gardening all her life. Holding a degree in Biology, Nutrition, and Agriculture, Laura's area of expertise is vegetables, herbs, and all things edible. She lives in Ohio.