Comprehensive Guide to Plant Bolting

Why do plants bolt? Learn about the process, its purpose, and how to prevent your plants from bolting.

It seems to happen overnight. When you go out to the garden to pick some greens for a salad, you notice a tall flower stem growing from the lettuce. In a few days, the blossoms will go to seed, and the leaves will be little and bitter. Your lettuce turns inedible, so you dig it up and dump it into the compost.

Where did things go wrong?

Up to this point, nothing has gone “wrong.” Your lettuce was doing what plants do – reproducing.
Every plant has a life cycle. The majority of our vegetable plants in the garden are annuals. They produce leaves, blossoms and fruit, set seeds, and perish all in the same growing season.

We’re happy to see them flower when it’s vegetables grown for their flowers, fruits, and seeds – like tomatoes, cucumbers, and squash.  We’re hopeful that we’ll have some delicious homegrown vegetables soon.

However, when leafy crops go to seed, it can spell the end of your harvest. It’s referred to as bolting. And it renders the plant’s edible portion, the leaves, stiff and bitter.

What is Bolting?

Bolting is the quick development of a flower stem on leafy crops. The plant has been told to set seed and finish its life cycle.

When your leafy veggies begin to blossom, the juvenile period is gone. It is time to produce the next generation, and the plant is responding to natural cues to do so.

And what about that unpleasant aftertaste? This is due to the substances produced by the plant to defend it from pests that may consume it during this vital reproductive period. You are a pest to a plant!

Why Do Plants Do It?

Bolting is not a bad thing. It’s just the plant going through its natural reproductive cycle.

Plants do this because they are nearing the end of their life cycle. Plants can bolt when they are biologically triggered by day duration – a phenomenon known as photoperiodism – or when they are stressed.

When plants bolt because of photoperiodism, there isn’t much a gardener can do. Spring crops such as lettuce, spinach, and some radishes complete their juvenile stage and begin reproduction as the days lengthen.

As the days get shorter, other plants communicate that it’s time to go to seed. Make sure you plant at the proper time to guarantee you obtain the whole yield before this happens.

When plants are stressed, however, there are steps a gardener can do. Too much or too little water, too much or too little fertilizer, too hot or too cold temperatures, bug infestations, and disease concerns are all examples of stressors. Basically, any unfavorable conditions might cause bolting in a plant that is prone to it.

Lettuce that is starting to bolt so it can spread seeds

Plants That Bolt and When

Consider more than just what to plant when designing your food garden. Take into account the season in which you cultivate various vegetables. Plants that are prone to bolting must be planted at the appropriate time.

Annual Vegetables

These vegetable crops go through their entire life cycle in a single growing season. When the weather warms up in late spring/early summer, they may bolt:

  • Lettuces, arugula, and fennel
  • Basil and cilantro
  • Bok choy and spinach
  • Broccoli
An example of a small floret in the middle of lettuce signifying the beginning of this process.

Biennial Vegetables

Biennial plants have a life cycle that takes two growing seasons to complete. The first year, they produce vegetative growth, and the second year, they blossom and set seed.

Many of the vegetables we cultivate are biennials, but we harvest them in their first year. These are some examples:

  • Root vegetables like beets, turnips, carrots, parsnips, and rutabaga
  • Onions, leeks, and shallots (shallots won’t form a good bulb once it flowers)
  • Brussel sprouts, cauliflower, celery, and leeks
  • Kale, endive, swiss chard, and collards
  • Cabbage, kohlrabi, and parsley

Cold weather can trick these plants into thinking the second year of their lifecycle has commenced, causing them to bolt. For this reason, be certain that you plant them at the appropriate time for your region.

Your county extension department can assist you in determining the best time to plant for a longer, more flavorful crop.

Minimize stress whenever possible and plant earlier in the season.

How to Prevent It?

Once a plant has been triggered to set seed, it can’t be stopped.  It is impossible to stop a plant from setting seed once it has been initiated. Cutting the bloom stem will not prevent the plant from going to seed. However, there are things a gardener can take to postpone the process.

  • Plant varieties that are slow to bolt. “Bolt resistant,” “long standing,” and “holds well” are all phrases that will appear in plant descriptions.
  • Mulch helps to keep plant roots cool. Plants are more sensitive to soil temperatures than they are to air temperatures.
  • Row covers, cloches, and shade cloth can be used to protect annuals from the sun and biennials from the cold. Row covers can also provide shade in the late afternoon.
  • Fertilize your green crops with a high nitrogen fertilizer to promote vegetative development. Select a fertilizer with a higher first number. Use a fertilizer with a high middle and third number if you want to enhance blossom and fruiting.
  • Maintain your harvesting pace. If you harvest the outer leaves on a regular basis, your plants will stay in the juvenile vegetative stage for a longer period of time.
Protecting from the heat of the sun can delay the process from starting.

Bolting Has its Benefits!

A flowering plant attracts pollinators. Their presence is good to the general wellbeing of your garden. Also, a plant that has gone to seed means free seeds for your garden the following season.

The bitter leaves are no longer suitable for salads, but they can be added to soups and stews where their powerful flavor can be savored.

Alaine Connolly
Alaine has been working way too hard in horticulture since 1992, beautifying golf courses, resorts, and hotels. She is a part time landscape designer who works full time caring for a 28,000 square foot public garden. At home, she maintains her own 400 square feet plot. Alaine lives in northern Illinois - zone 5b.
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