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Bolting – The Bad Kind of Flowers: What Is It, Why It Happens, and How to Avoid This Costly Problem

What is Bolting?

Bolting is when plants produce a hearty, nutrient-gobbling flowering stem before harvest. This occurs as a natural attempt to produce seeds – a means of survival when a plant is put under stress and feels that it is in danger. For this reason, many gardeners will also call this dreaded behavior “going to seed”. Why is this so detrimental to your harvest? Because once flowering is triggered, nutrients are diverted away from the stems and other vital parts of the plant that can be consumed and sold.

Why it Happens?

Stressors include changes in day length, exposure to low temperatures or excessively high temperatures at particular stages in a plant’s growth cycle. Disease problems, insect infestations, and insufficient water or minerals are also likely culprits.

While this is natural protective behavior for the plant, it can ruin entire harvests and also the taste of the plants. The taste becomes bitter and the plant itself will be tougher and harder to chew. In short, your harvest will be a lot less tasty and a lot less valuable.

Plants that are highly susceptible to bolting are lettuce, assorted herbs, beetroot, brassicas, spinach, celery and onion. Spinach, for instance, thrives in temperatures between 35 and 75 degrees. It’s no surprise that temperatures that border on freezing will endanger the plant, but this works just as much on the opposite end of the spectrum.

Overcrowding can also influence the health of plants by forcing plants to compete for nutrients, sunlight, water, and room for roots to spread.

Another example is cabbage. Bolting here is determined by how many days have passed outside of a certain threshold temperature. Six weeks of exposure to temperatures outside of this plants comfort zone and bolting is inevitable – whether it happens right away or in a few weeks’ time. That’s right, once the plant has decided to go to seed, it will happen no matter what you do. 

How to Prevent the Bolt?

As spinach and cabbage are both extremely sensitive to over-exposure and excessive sunlight, one way to avoid bolting is to wait longer into the season to put down seeds. Days are short and cool – prime growing scenarios for this plant.

Here's four other steps to take:

Row covers

Direct sun during long summer days will wreak havoc on your plants. Protecting them from the onslaught of sunlight will go a long way. Row covers are frequently used to keep cold weather crops producing longer. Here’s an affordable, do-it-yourself option for those interested.

Correct Spacing

As mentioned earlier, proper spacing also goes a long way. When plants are crowded together you get competition effects either for light or for nutrients and yields are reduced. Want to know the optimum distance to place your seeds? Check out this exhaustive plant spacing guide.

Mulching

With a plant such as broccoli, the temperature of the soil will influence how likely the plant is to bolt. The hot weather effect on broccoli will only happen if the heat gets to the roots. One simple way to avoid overheating of the soil is to place the plant in a well-mulched area. A dense layer of mulch will help keep the roots cool and prevent the broccoli from bolting.

Harvesting

For plants that flourish in cooler temperatures – such as spinach, lettuce, broccoli – harvesting early and frequently is a good way to avoid ruined harvests. These are all regenerative vegetables that can supply harvests throughout the season. When you cut the main head, other smaller heads will grow. In fact, the side heads will take a little longer to bolt.

Helpful Tip: When purchasing seeds, look for ‘slow to bolt’ on the labeling. These varities are supposed to take longer to go to seed. But tread carefully and don’t overpay. In many cases, the claims cannot always be sustained or proven. But if you have the option, go with the slow bolting seeds.

Bolting is avoidable and manageable when you know what the main causes are, the signals that a plant is under stress, and preemptive steps that will help avoid this problem. If your plant is under stress, for whatever reason, the cure is simple... eliminate the stress with the steps listed above.

How about you? Do you have some helpful tips or experience with avoiding the harvest-plaguing bolt? We’d love to hear them in the comments below!