Plant Bolting: Why It Happens and What to Do About It

Green garlic arrows
_curly_ / Getty Images

Bolting, also known as "going to seed," occurs when a plant matures and produces seed. It frequently occurs you grow cool-weather vegetables. While bolting can happen to many kinds of crops including onions, beets, leeks and other root vegetables, it's a problem most commonly faced by annual leafy crops, like lettucespinach, and arugula.

What Is Bolting?

Bolting refers to a vegetable plant's sudden growth of a flower stalk. Seed formation follows the flowers and the desired growth of the vegetable itself stops.

The first thing to realize is that bolting is a problem for you, not for the plant. For the plant, bolting is perfectly natural and desirable. The leafy vegetable's very reason for living is to reproduce by forming seeds, which is what happens when bolting occurs.

But this conflicts with your own desire as a gardener, which is for the plant to produce, not seed, as many of those tasty leaves as possible. Once the plant goes to seed, this production ceases. You and the plant are thus working at cross-purposes. The challenge is to use your skill as a gardener to stack the deck in favor of your purposes, thereby frustrating those of the plant for as long as possible.

There are many factors that can trigger bolting in a plant. One of the biggest triggers is simply a change in a plant's environment. The sudden onset of hot summer weather comes immediately to mind, but even the gradual increase in the number of daylight hours as spring yields to summer is a factor. At the most basic level, bolting is brought on by stress.

How to Identify Bolting

The good news about identifying bolting is that it is easy to do. The bad news is that, once you have identified bolting on a plant, it is largely too late to do much about it. You know bolting is occurring when:

  • You see a tough stalk, studded with just a few leaves, suddenly shoot up out of the plant's foliage
  • You see this stalk start to form buds, which first become flowers, then seeds
  • You see that the growth rate of the rest of the plant has clearly slowed down
  • You notice that the taste of the remaining leaves is becoming more or more bitter

Why Bolting Is Bad

Unless you wish to collect seed from the plant (for future crops) or let its flowers attract pollinators to your garden, everything about bolting is bad for you as a vegetable or herb gardener. To send up the flower stalk that signals bolting, the plant is squandering resources that would otherwise be put into nourishing its leaves and roots.

But the squandering of resources isn't the only problem with bolting. After a leafy vegetable bolts, it stops producing those nice, big, tasty leaves that you are growing it for. The remaining leaves will be smaller and tougher. Any further leaves produced will also have such a bitter flavor that you will not want to eat them. Ultimately, once an annual plant bears seed, it will die, its mission in life having been achieved.

How to Prevent Bolting

Since it is part of its natural life cycle for a leafy herb or vegetable, bolting will eventually occur no matter what you do. The goal is to delay it for as long as possible. To this end, there are several measures you can take. You will have greater success if you take multiple measures.

Planning ahead is often the gardener's best ally, and that is certainly the case here. Delaying bolting on lettuce, for example, begins with the type of lettuce you select. Some varieties are supposed to be bolt-resistant, like 'Slobolt.' Planning ahead is often the gardener's best ally, and that is certainly the case with bolting. Choose bolt-resistant varieties like 'Boltardy' beets and heat-treated onion sets. Delaying bolting on lettuce, for example, begins with the type of lettuce you select. Some varieties are sold as bolt-resistant, like 'Slobolt.' A better bet may be simply to stick to leafy lettuces like Grand Rapids, Oakleaf lettuces, Romaine lettuces, and Summer Crisp rather than head lettuces.

Do not sow a single crop of lettuce and then stop sowing. Instead, plan to continue to sow at intervals so as to stagger the crop. If the first crop bolts, at least you have another harvest coming along. Also plan to harvest leaves (especially the larger, outer leaves) regularly: the plant is more likely to think it's time to produce seed if large leaves are allowed to remain on it for days.

Although we usually think of vegetables as full-sun plants, lettuce can grow in partial shade. Take advantage of this fact to delay bolting and extend its growing season. One stress factor that triggers bolting is heat, and a plant growing in the shade will be subjected to less heat. If you lack a shady spot to grow your crop, use a shade cloth.

Another stress factor is a lack of water or nutrients. To address both needs at once, apply compost around your plants and water it in. Keep the soil evenly moist, but don't overwater.

If (or when) all else fails and you see flower buds developing on a plant, pinch them off to extend your harvest a bit longer.