What is Bolting? How to Prevent Plants from Bolting

Have you ever heard gardeners talk about plants “bolting”, but aren’t exactly sure what that’s all about? Then you’ve come to the right place! In a nutshell, bolting is when a plant flowers and goes to seed too early. It isn’t ideal, but there are a number of ways to help slow or prevent bolting. Read along to learn more about why plants bolt early, which plants are most susceptible, tips to prevent bolting, how to make the most of it (hint hint: seed !) and other frequently asked questions. 

What is bolting?

Bolting is a horticultural term for when a plant prematurely develops a flowering stalk (in a natural attempt to produce seed) before the crop has been harvested. The plant shifts its energy from growing the desired crop to reproduction instead – its final hoorah, if you will. Bolting may also be referred to as “going to seed”. Usually, a small flowering bud will form in the center of the plant or stem, and then grow increasingly tall very quickly. Bolting is especially common in heat-sensitive vegetables like broccoli, cauliflower, lettuce, bok choy, and other leafy greens. 

New gardeners are often surprised to learn that ALL annual garden vegetable crops eventually flower – even carrots, radishes, potatoes, beets, cabbage, spinach, onions, and lettuce! That is their way to naturally reproduce near the end of their life cycle: by forming flowers and seed. However, those crops usually flower at the end of the growing season, after many months of providing food or a good harvest first. Yet sometimes plants are triggered to start that process too early (aka bolt) and skip right past the stage you’re hoping for. Bummer!

On the other hand, plants that produce seed-containing fruit (e.g. tomatoes, peppers, squash, cucumbers, or eggplant) produce flowers and seed sooner and throughout the season, and are welcomed with open arms! They’re simultaneously offering you their bounty and fulfilling their goal to reproduce. 

What causes plants to bolt or go to seed?

A variety of things can trigger a plant to bolt and begin to flower. Namely, it occurs when the plant is stressed or otherwise unhappy with the conditions it’s provided. The most common causes of bolting include temperature swings, heat waves, warm soil, and crops grown during the wrong season (e.g. planting cool-season vegetables during summer). Plants that receive too little sunlight or too much shade, inconsistent watering, inadequate nutrition, or those that are root-bound as seedlings may also be prone to bolting.  

How bolting effects plants

When a plant bolts, it grows a flower spike and seeds at the expense of the rest of the plant. Most plants become increasingly bitter in flavor, especially lettuce, spinach and other leafy greens. They sometimes become more tough too. Therefore, you may want to harvest as much as possible when your greens first show signs of bottling. Though I personally don’t find the slight change in flavor to be a deal-breaker! We happily continue to harvest and eat greens from our bolting kale, bok choy, basil, and arugula – sometimes for many months. 

Another noticeable change is that new leaves become smaller and more pointed, as seen in the photos of our bolting bok choy and cilantro below. Some plants may fail to form a harvestable crop at all. For example, a bolting broccoli plant may not form a nice tight head, and instead turn into a tall and loose flower stalk. The long-term storage of crops may also be impacted, such as when onions form a tough flowering stalk in the middle of the onion bulb. You can still eat the onion, but not cure it for dry storage.

Is it bad if a plant bolts or goes to seed?

I recently saw something that referred to bolting as “the bad kind of flowers” – and I have to disagree, at least in part! While it can be unfortunate when plants go to seed before you’re ready for them to, it isn’t allll bad. Crops are still edible after they bolt, even if they’re not in their prime. Not to mention, the bolting stems and flowers themselves are edible! Older flower stalks can be a little tough sometimes, but make the perfect addition to soup, stew, roasts, and more.

Also, pollinators love the flowers on bolting plants. Our bolted brassicas (such as kale and bok choy) are always absolutely buzzing with bees! We often leave bolted plants in the garden long after we need them, just for bees to enjoy.

Finally, bolting plants provide you an opportunity to save seeds. Seed-saving is a whole topic in it’s own right, and the method can vary from crop-to-crop. In most cases, it’s best to allow seeds (and/or seed pods) to fully develop and dry out while still on the plant to produce viable seeds. You’ll have the most success in saving seeds from open-pollinated heirloom varieties over hybrid cultivars, which may not “breed true”.

Aside from looking on the bright side, I get it… bolting can be frustrating, especially when you have a limited amount of garden space or plants! So, let’s dive into six different ways to prevent plants from bolting. 

6 Ways to Prevent Plants from Bolting

1) Choose climate and season-appropriate plants

Before planting crops, do your homework to see what type of conditions and temperatures they prefer. Attempting to grow something that thrives in cooler weather during the summertime is only setting yourself (and the plant!) up for failure. Instead, grow heat-sensitive plants in spring and fall. Or, consider a winter garden! Folks in frost-free zones can grow a plethora of crops right through the wintertime, and with a little extra ingenuity and frost-protection, so can gardeners in colder climates! Thankfully, most heat-sensitive crops are tolerant of light frost. Use your Homestead and Chill planting calendar to determine the best time to plant a variety of crops, for any zone.

2) Provide shade and good hydration during heat waves

Even with the best planning, and despite growing the “right” types of crops for a particular season, an unexpected heat wave can come through and thwart all your good efforts. So, be prepared for heat waves and offer heat-sensitive plants some extra love and protection when one arrives. I’m working on an article all about how to protect your garden during a heatwave (coming soon!), but here are a few tips in the meantime: 

• Offer heat-sensitive crops extra shade by putting up temporary shade cover, such as shade cloth supported on hoops or stakes, or even a patio umbrella. 
• Water your garden extra long and deep the day or morning before the heat wave hits.
• Mulch the soil to reduce temperature swings in the root zone.

3) Select heat-tolerant or bolt-resistant varieties

While “lettuce” or “broccoli” are generally cool-season crops, there are specific varieties of every vegetable that have superior resistance to heat and bolting. Look at plant descriptions for those characteristics, especially if your area is prone to unpredictable weather patterns. For instance, our favorite variety of bok choy (Joi Choi) is described as “tolerant to heat” and is much slower to bolt than others, allowing us to grow it from spring into early summer, or during our warm fall weather into winter.

You can find heat-tolerant cultivars of radishes, kale, broccoli, cauliflower, cabbage, lettuce, spinach, and more! Some of our go-to slow-to-bolt favorites are Belstar broccoli, Coastal Star romaine lettuce, Sparx green leaf lettuce, Sora radishes, Red Giant mustard greens, Red Splendor mustard greens, Georgia collard greens, and Peppermint Swiss chard.

4) Provide regular moisture and mulch 

Did you know that plants are more sensitive to temperature swings around their roots and in the soil than they are to air temperature? It’s true! So, help maintain steady soil temperatures by using an inch or two of mulch around the base of plants, such as compost, wood chips, straw, or shredded leaves. Mulch insulates the soil to buffer against temperature swings, and also helps maintain more even and steady moisture levels. Read more about popular types of garden mulch here. 

Damp soil also promotes consistent temperatures. Develop a regular watering schedule to further reduce plant stress and prevent bolting. Slow and deep water a few times per week is better than watering a small, shallow amount every day. It promotes deep root growth patterns, which further protects plants from heat or drought stress. Check out this article all about garden irrigation for more ideas and tips.

5) Provide the recommended amount of sunlight 

Plants may bolt if they don’t receive enough sunlight. When plants are craving more, they grow tall and lanky (aka leggy) – stretching in search of the sun. The lack of light also reduces their ability to photosynthesize, use nutrients to grow or produce well, and generally creates stress. If a plant senses that it doesn’t have enough light and energy to produce a good edible crop, it will attempt to produce seed instead. Therefore, follow the recommended sun exposure for any given plant as much as possible!

Most vegetable crops prefer full sun, which is defined as a minimum of 6 hours of sunlight per day. When in doubt, provide as much as possible. (That is, unless afternoon heat is a concern. In that case, some afternoon shade may be preferred.) This goes for indoor-raised seedlings too, which need even more light! Seedlings should receive at least 12 hours of bright direct light, and will greatly benefit from the use of a grow light indoors.

6) Avoid stressed seedlings 

The final tip to prevent plants from bolting is to do your best to support their overall health, and reduce stress as much as possible. Whether you’re growing from seed or purchase started seedlings from the nursery, planting healthy, happy seedlings will help set them up for success from the start. When seedlings are stressed (such as being root bound in small pots, receiving too little light, or poor nutrition) they will be more prone to bolt after transplanting rather than flourishing in your garden. 

Therefore, avoid these 9 mistakes when starting your own seeds indoors, including hardening off seedlings before planting them outside. If you’re plant shopping at the local nursery, remember that bigger isn’t always better! Select the most tender, dark green, compact and healthy-looking seedlings over bigger ones. Large seedlings are more likely to be wiry, tough, root-bound and ready to bolt. Consider adding mycorrhizae to each seedling’s planting hole; it helps to reduce transplant shock and strengthen the plant’s resilience to stress. 

Learn more of our top tips for transplanting seedlings here! 

Can I cut the flowering stem to stop bolting?

You may be wondering if you can stop the bolting process by simply cutting off the flowering stem. The answer is no, unfortunately there is nothing you can do to halt the plant from bolting once it starts. It has already made that gear shift internally to seed production; there is no going back now.

However, cutting the early flowering buds or stem can slow the bolting process down a bit! In fact, it’s common practice to routinely pinch back the flowers from annual herbs like basil to extend your harvest. I find that removing the flower stalks from plants that produce dozens of small leaves (e.g. arugula or basil) is especially effective at prolonging the plant’s life. Yet cutting off the flowering stem from something like broccoli, cabbage, or cauliflower will not force the plant to grow a new large head. Instead, those may produce small side shoots, or more flowers.

And that is the scoop on bolting plants!

All in all, it isn’t ideal when your plants suddenly go to seed on you. Yet I hope you can see that there are many easy and creative ways to slow or prevent plants from bolting as we explored in this article. Plus, all is not lost if the pollinators get a little food out of the deal! Please let me know if you have any questions in the comments below, share your favorite heat-tolerant veggie varieties, or chime in if I forgot any tips that work well in your garden! If you found this information to be valuable, please spread the love by sharing or pinning this article. See you next time!