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Why Do Herbs Bolt & How To Avoid Bolting

white flowers on a green stem from basil that has bolted
Basil flowers are rather beautiful and can be pinched out, without any adverse effect on the flavor.

When herbs bolt it can be due to a number of factors, but it is also important to note that in some cases it can be a real positive. We have annuals that at the end of a season we allow to bolt as they then act as a perennial and self seed ready for the next growing season. In this article I wanted to look at the herbs that you may want to avoid bolting as it has a detrimental effect to the plant.

Herbs can bolt because of….

  1. Sudden increase in temperature, above what the plant would normally enjoy, can cause it to bolt. Planting in pots that can be moved to cooler parts of the garden can be a great solution.
  2. Lack of nutrients can cause bolting in herbs, a simple liquid feed made from organic material can help with this problem.
  3. Over exposure to sunlight can be a reason for a plant to feel stressed and bolt. Making sure that you fully understand the perfect climate for your herbs can help here. Not all herbs need 8+ hours a day some prefer partial shade in fact.
  4. We have had herbs respond to hot strong winds by bolting as the herb thinks it is nearing the end of it’s life. So we have moved to a more sheltered spot to avoid loosing out on the growing season.
  5. Herbs can bolt when they are coming to the end of their lives. This is not a problem unless you do not want it to potentially self seed in your garden.
  6. If your herbs are not particularly drought tolerant then they can bolt with a lack of water. It is a response that makes sense as the plant is trying to secure a future during a time without water. So it puts all of it’s energy into making seeds for the next generation. We use a passive watering system to reduce any concerns here and it works really well for herbs like cilantro and parsley.

What Does It Mean To Bolt

When plants bolt it is as a response to potential danger. Think about the list of reasons a plant would bolt, from drought, to over exposure to sunlight and lack of nutrients. All of these reasons will result in the plant possibly dying.

When a plant bolts it produces seeds and puts all of it’s energy into that production. Meaning that things like foliage production as second place, however this can even transform the flavor of the herb. Meaning a nice light flavor in cilantro now becomes sour and bitter to the taste. Even in some herbs like parsley meaning that the foliage becomes tough and inedible.

The problem with bolting is that it can also be completely pointless. Take garlic for instance. Garlic is sterile and can only reproduce via propagation using cloves. So why would it bolt and produce flowers and then seed? It is still a reaction to the problems above and can be avoid wholly by planting carefully and watering regularly.

when chives bolt vs when they flower
We plant our chives outside to let them flower for the pollinators.

Is Flowering The Same As Bolting

Plenty of herbs flower and produce edible flowers and foliage with no detrimental effects on taste. However when they are flowering to then produce seeds you will start to see a change in taste and texture of your favorite herbs.

Herbs That Happily Flower And Don’t Bolt

  1. Chives actually flower and produce tasty foliage at the same time. You can harvest chives throughout the growing season to reduce the chances of them flowering, but it is beneficial to the bees and the plant to flower. We say let them flower and enjoy them in salads and martinis alike.
  2. Mint can flower happily and still produce an abundance of foliage! We do not advise to plant mint in the ground as it is so invasive, so pinch out the flowers once they have started to die back. This will stop seeds from growing and the plant will become bushier as a result.
  3. Basil is similar to mint and will flower in quite an attractive way. We love to grow different varieties of basil and the flowers are firm favorites with pollinators, so let them grow but then pinch out to produce a healthier and bushier plant.
  4. Thyme flowers are really lovely small flowers that really perk up a salad or garnish. Subtle in flavor but big on appeal. Our patch of lemon balm looks perfect in pots or underneath trees as ground cover. It is important to note that it flowers annually but not as a form of bolting and will encourage foliage growth after the flowering season.
  5. Borage flowers are lovely and vibrant stars. Almost entirely the reason to grow borage, other than as the leaves have a cucumber like taste and work well in salads. In this instance the herb is an annual and would need to be sown again the following year, by allowing it to flower and then produce seeds we limit how much work we have to do as the gardener.
  6. Oregano and Marjoram will flower happily throughout the growing season with no negative effect on the taste of the leaves. We find that pollinators love the flowers and they are attracted to other plants in the area. Oregano is drought tolerant to a large extent and can happily move into full sunlight without having a flight or fight response in the form of bolting.
  7. Rosemary is a mostly drought tolerant herb and we find that even during periods of flowering we can harvest an abundance of leaves for cooking and drying.
  8. Fennel is an odd one. It will flower and be quite spectacular in its splendor, but it will then produce seed. We can eat the seed so we harvest the flower heads as they are starting to produce seeds and store the stems. When they are air drying we secure a paper bag over the flower head and the seeds fall into the bag as they dry. Then we can cook with the fennel seed. So in theory the fennel has bolted, but we are harvesting this and the plant can then live on if we carefully over winter it. Fennel is a perennial after all.

Herbs That Are Prone To Bolting

  1. Cilantro / Coriander will bolt very easily with a sudden change of temperature. Once that has happened the leaves are mostly inedible with a strengthening of flavor that makes them bitter. The leaves become almost tough as well.
  2. Parsley will bolt when there is little nutritional content in the ground and they haven’t been adequately pruned back. Parsley is not really a problem when it goes to seed as it is a biennial and can be overwintered ready for the next season. Make sure to grow some indoors if you want a guaranteed year round crop.
  3. Sorrel will bolt if it is in full sunshine. At that point the leaves are prone towards woody tough textures. To combat this you can cut the main stem out from each leaf, but it really does intensify the already quite sharp flavor and make it close to inedible.
  4. Tarragon can be extremely unhappy in full sun and will bolt right before your eyes. Once that has happened you will need to cut it back as it will become woody and scraggy.
lemon thyme flowering not bolting
You can see the fresh green foliage is still coming through even during flowering. Lemon thyme rocks!

How To Look After An Herb That Is About To Bolt

  1. If the weather is suddenly unseasonally warm, you can try to move your herbs to a new location in the garden. Equally you could try to provide some shade for them and ensure to monitor for suddenly shooting up stalks.
  2. Ensure that your herbs and vegetable garden is well watered through drought periods. The herbs that are most likely to bolt are essentially the same as leafy greens, so keep them well watered but not soggy.
  3. Avoid extremes of temperature by covering them in colder periods. A cloche over winter will go a long way to protecting an herb.
  4. Keep your herbs well pruned. Taking new growth not only encourages your herbs to be bushier, it also discourages them from bolting.
  5. If you are planting annuals, try successional sowing. This will require you to plant through the season. Really it does not avoid bolting due to old age, but it means you still have new plants coming through.
  6. Keeping your herbs well fed can avoid bolting. It is one stress that we can avoid for your herb and by feeding them a nice liquid feed we can ensure that they don’t feel they are at the end of their growing season prematurely.
  7. Use a mulch to minimize loss of surface moisture. This will be something that can also add to the nutritional content of the soil too. We use borage as a green manure and mulch directly. This also helps to reduce the effect of too much sunshine on the temperature of the soil.
  8. Pinch out flowers and flower stems as soon as they appear. For leafy greens like sorrel the stem is actually very tall and almost unsustainable by the plant so will snap very easily.
  9. Decide if you actually want a few plants to bolt and produce seeds. Coriander seeds are useful to next seasons crop and you will find it beneficial to let some herbs like parsley self seed.
sorrel that is about to bolt.
Sorrel is easily scared into bolting and the flower stem is massive. Meaning that the leaves are drained of resources and all energy is put into these huge stalks.

What Next

Make sure you grow the right herbs for your family. Go for some classics and make sure to plant them in areas where they will thrive.

Just don’t be too afraid of bolting as sometimes you get some very pretty effects!

For more information on garden jargon and what certain terms mean check out this article.

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