Why does my coriander bolt before I can pick it?

Coriander is a short-lived annual whose entire purpose, from the plant's point of view, is to flower and set seed. Anything that tells it conditions are getting difficult — heat, drought, cramped roots, being moved — brings that forward. It is not a plant you keep going; it is a plant you keep sowing.

What you'll need

• Coriander seed, ideally a leaf variety
• A pot at least 200mm deep, or a patch of open ground
• Peat-free compost or improved soil
• Fleece or netting for shade in high summer (optional)

Step by step

1. Sow direct, where the plant is to grow.Coriander has a tap root and hates being moved. Transplanting a module-grown plant, or buying a supermarket pot and splitting it, is the single most reliable way to make it bolt within a fortnight. Sow into the final pot or into open ground.
2. Use a deep container if you are growing in pots.At least 200mm and preferably 300mm deep. A shallow tray or a small pot restricts the tap root and dries out quickly, and both prompt flowering.
3. Sow a little and often.A short row or a small pot every two to three weeks from April to August. This is the actual answer to the problem: you accept that each sowing gives you a few weeks of leaf and you keep a succession going.
4. Choose a leaf variety rather than a seed variety.Cultivars sold for leaf production — often described as slow-bolting or as leaf coriander — genuinely last longer before flowering than varieties grown for seed. It makes a noticeable difference.
5. Give it shade in high summer.Full sun in April and May is fine. In July, a position with morning sun and afternoon shade, or a piece of shade netting, delays bolting substantially. Heat is the main trigger.
6. Keep the soil evenly moist.Drying out even once is often enough to send a plant into flower. Coriander in a pot in July may need watering daily.
7. Sow thinly and do not crowd it.Thickly sown coriander competes with itself for water and root space and bolts early. Thin the seedlings to about 50mm apart.
8. Harvest the outer leaves, taking no more than a third at a time.Cutting the whole plant to the ground either kills it or triggers flowering. Picking the outer stems from several plants keeps them all producing.
9. Use the plant when it does bolt.The flowers are excellent for hoverflies and other beneficial insects, and the green seed is a good flavour in its own right. Let a proportion run on and collect the ripe seed as coriander spice, which stores for a year or more.
10. Sow in late summer for an autumn crop.An August or early September sowing grows into cooler weather and often lasts far longer than a summer one. Under a cloche or in a cold greenhouse it can crop into the winter.

Tips

• Dill, chervil and rocket bolt for the same reasons and respond to exactly the same treatment — direct sowing, succession, shade and water.
• Parsley is a biennial rather than an annual: it grows leaf in its first year and bolts in its second, which is why an overwintered parsley plant flowers in spring. Sow a fresh batch every year.
• A supermarket coriander pot contains dozens of seedlings crammed together and will bolt whatever you do. Use it up rather than trying to grow it on.
• Coriander is one of the best plants in a vegetable garden for attracting hoverflies, whose larvae eat aphids. Letting some flower is a genuine benefit, not a failure.

Common mistakes

• Transplanting coriander seedlings — Disturbing the tap root is a direct bolting trigger. Sow where it is to grow.
• Sowing once in spring and expecting leaf all summer — It is a short-lived annual. Successional sowing every two to three weeks is the technique, not a workaround.
• Cutting the whole plant back to harvest — It responds by flowering or by dying. Pick outer leaves from several plants instead.
• Growing it in a small shallow pot in full sun — Restricted roots, heat and drying out are the three main triggers combined into one.

Questions people ask