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Herb Care 101: What is Bolting and How to Manage It

Bolting is a common challenge that herb gardeners face, transforming productive plants into tall, flowering stems seemingly overnight. But what exactly is bolting, why does it happen, and can it be prevented?

Herbs bolting in a terracotta pot.

Bolting meaning:

Bolting occurs when an herb or vegetable plant prematurely produces a flowering stem, before it can be harvested.

Have you ever stepped out to your herb garden, eager to harvest some fresh basil for your pizza, only to find your once-lush plant suddenly tall, sparse, and bitter-tasting?

You might be facing a common gardening challenge: bolting. This sudden growth spurt can diminish the flavor and usefulness of culinary herbs.

Herbs bolting vs flowering

Flowering and bolting are related processes in herbs, but they have distinct characteristics and implications for gardeners.

Flowering is the natural process where a plant produces flowers as part of its life cycle. This is normal and expected. It occurs when the plant reaches maturity and is ready to reproduce.

The flowers attract pollinators like bees or butterflies, which helps in the production of seeds and fruit.

What is bolting?

Bolting, on the other hand, is premature flowering. It happens when an herb plant quickly produces a flowering stem before it’s ready for harvest.

When herbs bolt, they divert energy from leaf production to seed production, often resulting in bitter-tasting leaves and reduced yields.

Bolting in herbs can be triggered by various environmental factors and stressors, including:

  1. Sudden increases in temperature
  2. Changes in the amount of light a plant receives daily
  3. Water stress – both under-watering and overwatering
  4. Poor soil quality or improper fertilization
  5. Transplant shock
  6. Overcrowding

What’s the difference, and is it a problem?

The key difference between bolting and flowering lies in timing and desirability. Flowering is generally a planned and welcome stage, while bolting is usually unwanted and can signal the end of the herb’s productive leafy stage.

For many herbs like basil or cilantro, this process can also change the taste, making them bitter or bland.

Gardeners typically try to prevent bolting in culinary herbs to extend the harvest of flavorful leaves.

However, flowering at the right time is encouraged for the production of flowers and seeds for next year’s crop.

Signs of bolting

Recognizing the early signs of bolting can help you take prompt action to extend your herb harvest. During hot weather or seasonal changes, keep an eye out for:

  1. Rapid vertical growth: The plant suddenly starts growing taller much faster than usual, often doubling in height within a short period.
  2. Stem changes: The main stem becomes thicker and more rigid. In some herbs, you may notice a hollow center developing in the stem.
  3. Leaf changes: New leaves may appear smaller, narrower, or have a different shape compared to earlier growth. They might also taste more bitter.
  4. Reduced leaf production: The plant focuses energy on stem and flower development, resulting in fewer new leaves, and the leaves produced are widely spaced.
  5. Flower bud formation: Small flower buds begin to appear at the top of the plant or along the elongated stem.
  6. Change in flavor: Leaves often become tougher and develop a stronger, sometimes unpleasant flavor as the plant prepares to flower.
  7. Color changes: The overall color of the plant may become lighter or yellower, particularly in the newer growth.

What to do if your herbs start bolting

If you catch the signs of bolting very early, you can often delay or slow the process.

  1. Pinch off flower buds: Immediately pinching any flower buds and the topmost growth can redirect the plant’s energy back to leaf production.
  2. Harvesting: Aggressively harvesting leaves, especially from the top of the plant, can sometimes encourage bushier growth.
  3. Reduce environmental changes: If possible, provide some shade and ensure consistent watering to reduce stress.

Even if you can’t completely stop bolting, these actions can often extend the useful life of the plant giving you time to take a final harvest from the plant.

In some cases, especially in hot weather, bolting may be inevitable. You might choose to let some plants bolt for seed collection.

Herbs that are prone to bolting

Several herbs are particularly prone to bolting and/or are significantly affected by it. Here’s a list of such herbs:

  1. Cilantro/Coriander: Extremely prone to bolting, especially in hot weather. The leaf flavor changes dramatically when bolting occurs.
  2. Basil: Bolts quickly in hot weather. While still usable, the leaves become more bitter and less aromatic.
  3. Parsley: Both flat-leaf and curly varieties bolt in response to heat and long days. Flavor becomes less intense.
  4. Dill: Bolts rapidly, especially in hot, dry conditions. While the seeds are useful, leaf production decreases significantly.
  5. Chamomile: Prone to bolting in hot weather. While the flowers are desirable, leaf production decreases.
  6. Arugula: Bolts quickly in warm weather, becoming excessively bitter and tough.
  7. Mustard greens: Bolt rapidly in response to heat and long days, becoming very bitter.
  8. Fennel: Prone to bolting if stressed. While still usable, leaf production decreases.
  9. Chervil: Very sensitive to heat and bolts quickly, losing its delicate flavor.