What Causes Vegetables to Bolt? What You Can Do About It


bolted lettuce going to seed

‘Bolting’ refers to running away. And while plants cannot essentially run away, bolting is, in fact, the plant’s survival mechanism that is triggered when it experiences stressful conditions. The term is used for plants beginning to flower and setting seeds too early, preventing the plant from bearing a vigorous harvest.

If the plant is under stress, like extreme temperature changes, changes in day length, or any other stress, it will bolt. It will then focus on producing the next generation (seeds and flowers) rather than growing leaves, roots, or stems.

Broccoli, cilantro, basil, cabbage, and lettuce are some of the plants known for bolting. Once a plant bolts, it becomes woody, tasteless, or even bitter, leaving vegetables inedible. However, at times, it is possible to delay or temporarily reverse the process of bolting.

Let us now discuss the various reasons that can cause vegetables to bolt and some ways to prevent or postpone bolting.

Reasons of Bolting in Plants

As mentioned earlier, plants bolt as a response to stressful and unsuitable weather conditions. It should also be said that annual crops flower naturally in the first year. On the other hand, biennials typically do not flower until the second year.

In biennials, bolting occurs when an over-wintering organ flowers before the winter. This usually happens with carrot roots. And in annual crops, bolting usually occurs before they are ready to gather. Moreover, some other reasons are responsible for plants to bolt:

·  Increased Day Length

As summer approaches, the days get longer, and exposure to sunlight also increases. This can potentially damage garden plants, especially annual crops. Also, cool weather crops such as lettuce and spinach will bolt in hot and dry spells. Moreover, this can also increase the temperature of the soil, which can further trigger bolting in plants. This is usually a problem observed in plants that were grown too late in the spring.  

·      Cold Temperature

While increased day length and excessive heat can damage cold weather crops and annuals, cold temperatures can also be harmful to biennials like onions, leeks, beets, and carrots. A sudden cold snap during spring can signal the plant that the winter season has commenced, triggering bolting. So, if you grow these plants way before the spring season has started, you will be exposing young seedlings to cold temperatures which damage them.

·      Root Stress

Transplanting can quite often disturb the plants’ root systems. Other than this, growing a plant in a smaller container can also cause root stress which can, in turn, lead to bolting. Thus, it is essential to ensure that you pick the right pot for your plant and take proper care while transplanting it.

·      Plant size

It is usually observed that larger plants are more likely to bolt than small ones in unsuitable weather conditions or temperatures.

·      Insufficient Mineral or Water Supply

As we all know, soil rich in nutrients and has a balanced moisture level promotes the healthy growth of plants. Thus, an imbalance, particularly during the summer months, can cause the plant to bolt. Other than this, an increase in salt levels in the soil can also stress the plant, especially in structures like hoop houses. Some of the plants that are more susceptible to bolting are cauliflower, rocket, and spinach. This is when they do not get enough moisture.

To ensure that your soil has balanced moisture levels, you should ensure that your garden gets at least one inch of water in a week. You can further increase the amount if you have sandy soil. Also, if the weather gets warm, you should ensure that the soil is soaked up in water to ensure that the plants are not stressed.

Ways to Prevent Your Plants from Bolting

There are quite a few things that can help prevent bolting. This is extremely important since once it has started, it can be impossible to stop it. You can try more than one method to ensure that your plants are not stressed, and you can increase your chances of having a healthy and bountiful harvest. Here are a few ways in which you can avoid bolting and encourage a healthy growth cycle:

1.    Grow Bolt-Resistant Varieties

One of the easiest ways to significantly decrease bolting is growing “bolt-resistant” or “slow bolting” seeds. All you need to do for such labels are the seeds that have developed resistance to conditions that may cause bolting.

For instance, if you are planning on growing onion, you should seek heat-treated onion sets. These are the varieties that are capable of withstanding high temperatures and much unlikely to bolt. Also, one should avoid red onions that are usually more prone to bolting than white or brown varieties.

2.    Use Mulch

Usually, plants like broccoli, cauliflower, and cilantro have heat-sensitive roots, making them more susceptible to bolting. To prevent the soil or roots from overheating, one can consider spreading a layer of mulch. This would only keep the topsoil cool but will also help in locking in moisture. A gardener should not have any bare soil in the garden unless seeds are about to germinate in a newly planted bed.

Suppose you have no idea about using mulch. I have a video about garden mulch ideas. You can watch it below.

3.    Plant During Cooler Months

In some regions, growing a plant during the early spring season can still be quite warm. Thus, it is essential to consider your local climate before sowing the seeds. Also, you can try growing spring vegetables in the fall. This is when extreme warm temperatures are not usually expected. You can grow brassicas such as kale, cabbage, and bok choy during spring or fall.

4.    Offer Shade for Cold-Weather Crops

As mentioned earlier, growing plants in hot-weather climates can overheat the soil and roots. This would require you to ensure that the plants get enough shade. While this is primarily for your cool-season crops such as spinach, lettuce, and radishes, vegetables like exposure to sunlight may also bolt if the weather is extremely warm or dry. So, it is vital to offer them natural shade. Planting these crops near taller plants can be a great trick. You may even consider planting them in garden beds in the area located in partial shade. Or you may even use draping shade cloth over them.

5.    Use The Right Fertilizer

If you wish to treat their crops with fertilizer, you must ensure that it is customized to your needs, i.e., growing leaves and stems. This will ensure that the plant is not encouraged for flower growth. For this, you would need a fertilizer with a high level of nitrogen content.

6.    Avoid Transplanting

potted plant removed from pot and held in female hands

As mentioned earlier, certain plants such as carrots, turnips, beetroot, radishes, and various herbs are prone to bolting due to root stress. These tend to grow the best when they are sown outdoors directly. So, it is better to avoid transplanting them, which is often associated with root stress. This will ensure that your plants grow without any disturbance.

How to Identify Bolting?

To prevent your plants from bolting, you first need to identify the first signs of it. And the good news is that it is easy to do. The bad news is that once you have identified bolting on a plant, it is essentially too late to do much about it. Here are a few things that you may notice when a plant is bolting:

  • Tough stalk with only a few leaves
  • Rapid and upward growth
  • Stalk start to form buds that first become flowers followed by seeds
  • Slow rate of edible and vegetative growth
  • Less desirable taste (bitter and unpalatable) of the remaining leaves

However, there are chances that it is already quite late, and you might not be able to do a lot to stop it.  But one can always try and temporarily reverse the adverse effects of bolting by harvesting often and pinching off flowers.

What to Do When Plants Bolt?

Plants bolt, and usually, there is not much that you can do about it. So, if your plants bolt even after trying all the methods mentioned above, you need to understand that this is not the end of the world. There are still quite a few things you can do to help you make the most of your plants.

You may still be able to rescue some of the leaves (peppery arugula or slightly bitter lettuce) by mixing them with other salad greens. Some people tend to prefer the taste of it over the bland-tasting lettuce available in the market. Other than this, you can chop up root vegetables and use them in stews. And when it comes to onions and leeks, you can chop out the usable parts and use them usually.

While you cannot control the climate or the weather conditions, changing your attitude is relatively easy. Other than using the remaining veggies, it would help if you also were pragmatic about the situation. One should learn to appreciate all the goodness that it can offer.

Bolted vegetables are often thought to be useless. However, they can be a boon for pollinating insects like bees. Consider them to be a feast for them while they also offer your garden with some attractive blooms. Some of the most eye-pleasing ones are said to be the bobbing globes of alliums, lace-like carrot umbels, and yellow brassica flowers.

Also, according to some, flowering bok choy stems are pretty sweet and tender, which would make for an excellent ingredient for stir-fry dishes or salads. This is why some gardeners often let vegetable plants flower for a little while before getting them out and planting a new crop.

Conclusion on what causes vegetables to bolt

As a gardener, one should understand that every plant has the genetic prerogative to make seeds. They react differently to different climatic changes. So, when a plant starts bolting, it is essential to know that this has nothing to do with your skills as a gardener.  One of the best ways to prevent it is by learning how mother nature works and going with it. Plan to grow cool-season plants in the cool season and not delay when they peak freshness and health.

We are sure that at least one of these tips will help you make the most out of your plants and will help you delay, if not prevent, bolting.

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Tony O'Neill

I am Tony O'Neill, A full-time firefighter, and professional gardener. I have spent most of my life gardening. From the age of 7 until the present day at 46. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

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