Why are my crops bolting?

June 20, 2024

In this article, we will explore why vegetative crops, such as broccoli, cabbage, cauliflower, lettuce, rhubarb, and spinach, shoot a seed head—also known as bolting. 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.

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.

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.

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 needs 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.

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.

In summary, 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.


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Source: Melvin Fisher | Sponsored by Keystone Bio-Ag LLC