At a glance
Coriander is one of the most frequently grown and most frequently failed herb garden crops in the UK. The pattern is familiar to most gardeners who have tried it – a pot of supermarket coriander brought home, a packet of seeds sown with optimism, and within weeks, regardless of care, the plant throws up a tall flower stem, the leaves become sparse and feathery, and the whole thing seems to have rushed through its lifecycle before you have harvested enough to make it worthwhile. This is bolting, and it is the defining challenge of growing coriander in the UK.
Understanding why coriander bolts – and the specific conditions that slow it down – transforms results from frustrating to reliable. Coriander is not actually difficult to grow. It germinates readily, grows quickly and is largely pest free. The challenge is entirely about timing, position and sowing frequency rather than any complex care requirement. Alongside coriander, the other quick-growing herbs covered in our guide to growing parsley share similar principles of succession sowing for continuous harvest.
Why coriander bolts and what to do about it
Bolting – the process of a plant switching from vegetative leaf production to flowering and seed setting – is triggered in coriander by a combination of long days, heat and any kind of stress. Coriander is a cool-season crop that evolved in the eastern Mediterranean and Central Asia, where it completes its life cycle in spring before summer heat arrives. In the UK, the long days of May to July trigger bolting almost regardless of what you do, particularly in warm weather.
The practical response to bolting is not to fight it but to work with it. Rather than trying to grow one large, long-lived coriander plant, the approach that works is to sow small quantities frequently – every three to four weeks from April through to August – and harvest each batch quickly and heavily before it bolts. Each sowing provides a flush of leaf production lasting two to six weeks, and with succession sowing you always have a fresh batch coming along as the previous one flowers.
Never transplant coriander. Root disturbance is one of the fastest triggers for bolting. Always sow coriander where it is to grow – directly into its final container or bed position – rather than starting it in a tray and transplanting. Even carefully done, transplanting significantly shortens the leaf-production period before flowering.
Sowing for maximum leaf production
Coriander seed is actually a dried fruit containing two seeds – gently crush the round “seed” between your fingers before sowing to split it and improve germination rates. Sow directly into the final growing position, 1cm deep, in clusters of three to four seeds every 20-25cm. Thin to the strongest seedling in each cluster once large enough to handle.
The best time to sow for leaf production is from April, once the soil has warmed to at least 10°C. Sowings made in very early spring – March indoors – often bolt rapidly when moved outside. Sowings from late April through to August give the most predictable results for leaf harvest. An August sowing in a sheltered position will often produce leaves into October before cold stops growth.
Coriander can also be grown indoors on a bright windowsill year-round. Sow directly into a deep pot – at least 20cm – as coriander has a long taproot and does not do well in shallow containers. A south-facing windowsill provides sufficient light in spring and summer. In winter, indoor-grown coriander grows slowly but remains usable, and is unlikely to bolt in the short days of a UK winter.
Succession sowing – the key to continuous supply
The most important technique for growing coriander successfully in the UK is succession sowing – making small sowings every three to four weeks rather than one large sowing at the start of the season. Each sowing will produce usable leaves for two to six weeks before bolting, and with regular new sowings in place there is always a fresh batch at the peak of leaf production while older batches are flowering.
Later sowings typically provide a longer leaf harvest window because the shorter days of late summer and autumn slow the bolting process significantly. An August sowing is often the most productive of the season in terms of leaf harvest per plant. This is the opposite of what most gardeners expect and is worth noting when planning the sowing schedule.
Position, watering and care
Coriander produces the longest leaf harvest in a position that receives morning sun but is shaded from the hottest afternoon sun – a semi-shaded position significantly delays bolting compared to full sun. This is different advice from most other herbs, which prefer maximum sun. East-facing positions, the north side of taller plants or a position shaded by a fence in the afternoon are all worth trying for coriander.
Keep the soil consistently moist – coriander that dries out bolts rapidly. Regular watering is more important for coriander than for Mediterranean herbs like thyme and sage. In containers, check daily in warm weather. Mulching around outdoor plants retains soil moisture and reduces the frequency of watering needed.
Harvesting leaves and seeds
Begin harvesting when plants are at least 15cm tall with well-developed leaves. Cut stems from the outside of the plant, leaving the growing centre intact to continue producing. Harvest frequently and heavily – regular cutting encourages bushy growth and delays bolting. Once a flower stem begins to emerge, pinch it out immediately – this buys another week or two of leaf production before the plant ultimately bolts regardless.
If a plant bolts fully, do not remove it immediately. The flowers attract beneficial insects, and allowing the plant to set seed provides a supply of coriander seed for cooking – the dried seeds have a completely different flavour to the leaves, warm and citrusy rather than fresh and herbal, and are used extensively in Indian and Middle Eastern cooking. Allow seed heads to dry on the plant, then collect and store in a sealed jar. These seeds can also be sown the following season.
Slow-bolt varieties worth growing
Selecting slow-bolt coriander varieties makes a meaningful difference to the leaf harvest period, particularly for earlier sowings when day length is longest. Several varieties have been bred specifically for reduced bolting tendency.
Confetti has finely cut, feathery leaves and good bolt resistance. Calypso is widely available and one of the most reliable slow-bolt varieties for UK conditions. Santo is a popular choice with good leaf production and slower bolting than common coriander. None of these varieties eliminate bolting entirely – they delay it – but combined with later sowing times and partial shade, they extend the harvest window meaningfully.
Common problems
Bolting is by far the most common issue and has been addressed above. Beyond that, coriander is largely trouble-free. Aphids occasionally colonise young plants but are rarely severe enough to damage the harvest – pinch off affected tips and the plant usually recovers. Slugs can damage seedlings, particularly in damp conditions. A ring of sharp grit around the planting area provides some deterrence, and the same broader approach to slug control applies to herb beds as to any other part of the garden.
Damping off – a fungal condition that causes seedlings to collapse at soil level – can affect indoor sowings in wet, poorly ventilated conditions. Use fresh compost, avoid overwatering and ensure good airflow around seedlings. Outdoor direct sowings rarely suffer from damping off.
Coriander seeds sold as a cooking spice may not germinate well. Whole coriander seeds from the spice aisle are often heat-treated or irradiated and may have very low germination rates. Always use fresh seed from a horticultural supplier or seed packet for sowing. The difference in germination rates is significant.
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