Bolting can happen suddenly and ruin an entire crop in a vegetable garden. But what is bolting and can we prevent it? Find out why bolting occurs, recommended seeds to sow, and best practices to lower the risk of bolting.
The plants affected by bolting are cool-tolerant vegetables and herbs that do best in spring and fall.
Bolting Vegetables & Herbs
What Is Bolting?
We use the term bolting when a vegetable produces flowering stems before we’ve had a chance to harvest the crop. We say “my lettuce has bolted” to mean it has shifted from vegetative growth to its reproductive stage and is no longer savory as a food crop.
Along with lettuces, other vegetables and herbs that can bolt are non-fruiting food crops we grow for their edible roots, stems, or leaves. This includes basil, broccoli, radish, and more. There is a list here.
There is nothing abnormal about flowering and producing seed—that’s basic survival through reproduction for plants. It’s the timing that’s the problem for the gardener when the end goal is food production.
What Does Bolting Look Like?
In plants like lettuces and spinach you may notice existing leaf stems suddenly elongate. Any new leaves are small and cling closely to the stem. The stem or stems will lengthen, eventually budding and blooming. Depending on conditions, this can happen within hours or days.
Unfortunately, by the time you notice it, it’s too late to stop.
What Causes Bolting?
The exact cause of bolting varies with different plant species and even between some varieties within each species.
Generally, bolting can be triggered by changes in day length, temperatures, and other stressors related to water and nutrition.
If a plant is in the right part of its life cycle and these other inputs reach particular levels, the plants says, enough is enough, it’s time to reproduce and save my life!
We tend to associate bolting with prolonged hot temperatures but cold snaps can contribute as well.
In a heat wave, our lettuces, unable to cope with prolonged high temperatures and long summer days, may morph quickly, changing from leafy greens to multi-stemmed flowering plants within days.
Some spinaches are at risk for bolting both in heat over 75°F (24°C) and cold snaps below 40°F (5°C).
Again, it varies by species and variety but each has its endurance limits and may flower prematurely to survive. There is a list of bolt-resistant seeds here.
Which Vegetables Bolt?
Vegetables and herbs that can bolt are annual or biennial, non-fruiting, cool-tolerant plants we grow for their edible roots, stems, or leaves. These are plants that do not require pollination to produce food.
Here are some examples:
- Bok choi (choy)
- Brussels sprouts
- Globe artichoke
- Onions (bulb-forming, shallots, leeks)
Food Crops That Do Not Bolt
Plants that flower and then fruit like cucumbers, eggplant, peppers, tomatoes, and squashes, do not bolt. In other words, we can’t have fruits without flowers forming first. These plants can also suffer heat stress and have issues with flowering, but we do not refer to this as “bolting.”
Can I Stop Bolting Once It Has Started? Should I Cut Off the Flowers?
Once a plant is flowering, you cannot coax it to resume vegetative growth. Even if you cut off the flower stems, the essence of the plant is already changed. Plus, flower stem removal may also trigger additional flowering side shoots to form.
Are Bolted Vegetables Safe to Eat?
While not unsafe to eat, once a plant has switched to its reproductive stage, the plant may be bitter or flavorless with a tougher (sometimes woody) texture.
There can, however, be a few minor exceptions.
Caught early, you may find things like basil leaves still somewhat palatable. I always taste test them just in case.
If left to set seed, plants like radish and arugula can produce some rather nice-tasting, zesty-flavored seed pods. This has more suggestions for unexpectedly delicious foods we overlook in the garden.
But overall, most of the time, bolting plants are not anything you’d want to eat.
My Vegetables Have Bolted. Now What?
If a plant has bolted, it still has value—just not the way we intended.
As mentioned, very occasionally, the plant may be salvageable as food but not usually.
Left to flower, it is useful for pollinators including birds and other wildlife.
From there, you may choose to save any open-pollinated seeds for future sowing or leave them for wildlife and/or self-seeding.
Alternately, remove the bolting crops, add them to your compost pile, and sow or plant something new that is suited to the current growing conditions.
How to Prevent Bolting
While you cannot get plants to stop bolting and return to a vegetative growth cycle, there are some things you can do preventatively to reduce the chance of future issues.
- Pay attention to the growing tips on your seed packets. Seed producers are very aware of bolting and give plenty of tips for the best timing and conditions to avoid issues.
- Sow cold-tolerant vegetables during cooler seasons like spring and fall. We call them “cool” or “cold-tolerant” because they do fine in cooler weather and often cannot cope with a lot of heat or longer days.
- Try growing what are marketed as bolt-resistant, slow-bolting, or heat-tolerant varieties, or heat-treated onion sets. While they won’t be 100% immune from bolting, some varieties are more tolerant than others. This lists some suggestions.
- Provide shade during long, hot days. Consider growing in containers to make it easier to move plants around as needed.
- Mulch your soil or potting mix. While heat stress and drought are not the same thing, they can occur together. Along with keeping plants watered (but not over-doing it), a two-inch layer of mulch over the soil or potting mix can help slow evaporation.
- Provide overall good plant care with healthy soil, proper watering, and good airflow to reduce stressors like drought, nutrient deficiency, and biotic stresses from fungi and other pathogens.
- Keep on top of your harvesting. Anything grown for the leaves and stems is edible at any time during the growing season. If you know hot spells are coming (as the days get longer), cut your losses and harvest early.
Check your favorite seed sellers for bolt-resistant varieties. There are lots more than I have listed here.
- Dark Opal Purple Basil | SeedsNow (US Shipping)
- Boltardy beetroot | SeedsNow (US Shipping)
- Belstar Hybrid Broccoli
- Covina F1 Broccoli | High Mowing Seeds (US & CAD Shipping)
- Green Magic Hybrid Broccoli
- Bilko F1 Cabbage | High Mowing Seeds (US & CAD Shipping)
- Slow Bolt Cilantro | SeedsNow (US Shipping)
- Tetra Dill Seeds | Botanical Interests (US Shipping)
- Black Magic Hybrid Kale
- Casper Kale
- Edox Lettuce
- Great Lakes 118 Crisphead Lettuce | Botanical Interests (US Shipping)
- New Red Fire Lettuce
- Yankee Hardy Lettuce Blend
- Red Giant Mustard Seeds | Botanical Interests (US Shipping)
- Bopak Hybrid Pack Choi
- Bloomsdale Long-Standing Spinach
- Space F1 Hybrid Spinach | (US & CAD Shipping)
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