Why Are My Crops Bolting and How to Prevent It

July 20, 2024

Have you noticed your vegetative crops, such as broccoli, cabbage, cauliflower, lettuce, rhubarb, and spinach, shoot a seed head? Well, that’s also known as bolting. Let’s explore what bolting actually means and how we can help prevent it.

This information can also help you grow a more healthy crop, and faster. For example, I have seen kale plants needing to be picked every 5 days instead of every 10 days using this method, as well as much less black rot pressure in broccoli.

What is Bolting in Crops?

First, an essential lesson in plant development: All plants will try to reproduce. This means that after we plant a seed, the seed germinates (hopefully), then the crop starts growing. Eventually it will want to reproduce.

Gardeners and farmers often face the frustrating issue of crops bolting, which can significantly impact their harvest. Understanding this phenomenon and learning how to prevent it can help you maintain a thriving garden throughout the growing season.

How to Prevent Plants from Bolting

The key to preventing bolting, of course, is to understand and work with this natural cycle of life. All plants have what we call a “days to maturity” (DTM). If you pick up a seed catalog, you will often find this DTM number listed by each variety. This DTM equals the approximate number of days till that crop will be ready to harvest for its intended purpose. For example, for peppers (a reproductive crop) the DTM will reflect the days to harvest for the actual peppers. For lettuce (a vegetative crop) the DTM will reflect the days till that crop should be ready to harvest as lettuce (as opposed to seed for harvest).

Here lies the key. A vegetative crop has to grow to its full vegetative maturity within that time frame, or you can expect it to bolt, give-or-take a few days depending on the heat units / growing degree days.

Plants Need Nitrogen, Calcium, Potassium and Chloride

So what can you do to prevent bolting? Ensure the plants have adequate levels of the four major growth minerals: nitrogen (particularly nitrate—not ammonium), calcium, potassium, and chloride. If these minerals are adequate and in balance, crop quality and speed of growth is greatly enhanced. These specific nutrients can easily be supplemented via drip irrigation.

Of course, all plants still need enough water and a basic balance of other nutrients and biology. From a nutrients perspective, you don’t want higher-than-average levels of manganese, phosphorus, and ammonium, since these three are the main drivers of reproduction and fruiting energy. This sounds easy enough, but can be difficult in actual practice during the summer, because ammonium tends to build up during hot weather. However, this is true only for plants with a low brix content.

Stress Makes Plants Bolt

Finally, we need to make the broad “disclaimer” statement and mention stress. Extreme stress of any kind can make the plants bolt, since a plant will always try to successfully reproduce before it dies.

Prevent Bolting in Lettuce

To prevent bolting in lettuce, start by selecting bolt-resistant varieties suited to your climate. Plant lettuce early in spring or late summer to avoid peak heat. Provide partial shade during hot periods using shade cloth or by interplanting with taller crops. Ensure consistent moisture with regular watering and mulching to prevent drought stress. Harvest outer leaves frequently to encourage continued leaf production. Use succession planting every 2-3 weeks for a steady supply of young plants. If temperatures rise, consider using row covers or moving container-grown lettuce to cooler spots. Lastly, maintain proper nutrition without over-fertilizing, as excessive nitrogen can promote bolting.

Prevent Bolting in Broccoli

To prevent bolting in broccoli, timing is crucial. Plant early in spring for summer harvest or in late summer for fall crops, avoiding peak heat periods. Choose heat-tolerant varieties for warmer climates. Provide consistent moisture through regular watering and mulching to reduce heat stress. Ensure adequate nutrition with balanced fertilizers, avoiding excess nitrogen. Protect young plants from temperature fluctuations using row covers. If unseasonable warm spells occur, provide temporary shade with cloth or by using taller companion plants. Harvest the main head promptly when it reaches full size, even if it’s smaller than expected. This encourages the development of side shoots and extends the harvest period.

Get Your Plant Nutrients from Keystone Bio-Ag

When plants have enough water and the growth minerals are balanced and in adequate supply, it is much easier to produce a vegetative crop without have problems with bolting. The crop will also be much healthier because it is growing rapidly, not just from nitrogen, but from calcium and potassium as well. This is particularly true when the nitrogen is in the natural or amino acid form.

Check out Keystone Bio-Ag’s liquid fertilizers as well as our dry fertilizers for added nutrients for your crops or contact us today for regenerative agriculture guidance.