How to Grow Coriander 'Slow Bolt'
from Seed
One plant, two completely different crops — citrusy, divisive cilantro leaves and warm, nutty coriander seeds are produced by the same plant at different stages of its life, with entirely different flavours and uses; grow your own for both, and stop the supermarket pot plant trap once and for all
The great confusion in the name "coriander" is that it refers to two quite different things from the same plant. In the UK, coriander typically means the fresh leaves — the pungent, citrusy, divisive herb that is either loved or loathed and appears in Indian, Mexican, Thai, and Middle Eastern cooking. In the US, the leaves are called cilantro and coriander refers exclusively to the dried seeds — warm, nutty, aromatic, and tasting almost nothing like the leaves. Both are right: it is the same plant, Coriandrum sativum, producing two entirely distinct culinary products at two different stages of its life cycle.
The plant goes through a visible morphological transformation as it matures. In its early vegetative stage it produces broad, flat, rounded basal leaves — the familiar coriander leaf of the supermarket bunch. As it prepares to bolt, the upper foliage changes character entirely: becoming finer, more feathery, and less pungent. Then the central stem elongates, the white umbel flowers open, and the seeds develop — first green, then beige-brown, the dried spice. The 'Slow Bolt' selection delays this transition significantly, giving a longer leaf harvest window before the plant moves on. But the bolt is not a failure — it is the second harvest, the one that fills a spice jar.
Quick Facts at a Glance
Plant Type
Hardy Annual — cool-season herb
Two crops
Leaves (cilantro) + Seeds (coriander spice)
Sowing Time
March–September direct; year-round indoors
Harvest
Leaves from 6–8 weeks; seeds in 12–16 weeks
Key rule
Direct sow ONLY — taproot hates transplanting
Difficulty Rating
2 out of 5 — easy with correct sowing method
Understanding the Two Crops
Coriandrum sativum is a member of the Apiaceae family — the same family as parsley, carrot, dill and chervil — native to southern Europe and western Asia, cultivated for at least 8,000 years, and found in ancient Egyptian tombs and Sanskrit texts. The leaves and the seeds are used throughout the world but the leaves are far more perishable — which is why growing your own makes so much practical and economic sense.
Crop 1 — Cilantro Leaves: Pungent, Citrusy, Divisive
The broad, flat basal leaves of young coriander — described as cilantro in the Americas — have a distinctive flavour profile: intensely aromatic, citrusy, fresh, and peppery, with an aldehyde compound (decanal) that produces the soapy character that some people perceive as strongly unpleasant. This aldehydic quality is genetic — approximately 10–20% of the population has a specific olfactory receptor variant that makes coriander taste like soap regardless of preparation or freshness. For the majority who enjoy it, home-grown fresh coriander leaves have a vibrancy and intensity significantly better than any supermarket bunch.
Crop 2 — Coriander Seeds: Warm, Nutty, Entirely Different
When the plant bolts and sets seed, the volatile aldehyde compounds that give the leaves their divisive character break down. The resulting dried seeds — light brown, spherical, ribbed — have a completely different flavour: warm, nutty, mildly citrusy without the sharpness, and gently spiced. This is the coriander of the spice rack, ground into curry powders, garam masala, ras el hanout, and dozens of spice blends. Home-grown coriander seed, freshly toasted and ground, has an intensity and freshness significantly better than pre-ground commercial product. The two crops taste nothing alike — and a single 'Slow Bolt' plant provides both.
⚠️ Direct Sow ONLY — Why Supermarket Pot Plants Fail
Coriander develops a long taproot from its very first days of growth. Any disturbance to this taproot — including the shock of transplanting from a pot to the ground — triggers an immediate bolting response: the plant interprets the root disturbance as a sign of imminent drought or stress and immediately runs to flower, producing almost no leaf harvest. This is why supermarket "grow your own" pot plants so often bolt within days of being transplanted outdoors. Direct sowing into the final growing position, where the taproot can develop undisturbed, is the only method that reliably produces a useful leaf harvest.
Sowing — Little and Often
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Direct sow outdoors March–September at 1cm depth. Scatter into shallow drills 1cm deep in prepared soil. Cover lightly. Water gently. Germination typically 7–14 days. Each coriander "seed" is technically a dried fruit (schizocarp) containing two seeds — so expect two seedlings per sown seed. Thin to 5–10cm spacing once established.
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Sow a small batch every 3–4 weeks — never the whole packet at once. This is the most important coriander cultivation rule. Coriander has a short productive leaf harvest window (six to eight weeks typically before bolting in warm weather). Sowing the entire packet produces a simultaneous glut followed by nothing. Small succession sowings every three to four weeks from March through August produce a continuous leaf supply throughout the season.
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Choose a slightly shadier position for summer sowings. In midsummer (June–August), the heat and long days accelerate bolting significantly. Partial shade in afternoon — behind taller plants, beside a low hedge, or on the shaded side of a raised bed — reduces temperature, slows the bolting trigger, and extends the useful leaf harvest window by two to four weeks. Spring and autumn sowings (March–May, August–September) in full sun are ideal; summer sowings benefit from shade.
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For winter supply: sow in a pot on a bright indoor windowsill. A 20–25cm pot of coriander on a south-facing windowsill at 15–20°C can be harvested year-round. Sow directly into the pot, maintain consistent moisture (never allow to dry out — drought triggers bolting immediately), and harvest outer leaves regularly. Replace every eight to ten weeks with a fresh sowing as the plant matures.
Harvesting Both Crops
Leaves (Cilantro) and Seeds (Coriander)
Harvesting leaves: Begin when plants are 10–15cm tall. Pinch or cut the outer leaves at the base, leaving the central growing point and inner leaves intact — the same cut-and-come-again technique as other herbs. Harvest in the morning when essential oils are most concentrated. Use immediately or keep unwashed in the fridge for two to three days. Once bolting begins (the central stem thickens and elongates, upper leaves become feathery), leaf quality declines — harvest all remaining basal leaves promptly.
Embrace the bolt for the seeds: When the plant bolts and flowers, the white umbel flowers open in clusters. These flowers are fully edible — they have a concentrated, fresh coriander flavour and make an excellent garnish for curry, dal, or salads. Allow the flowers to set seed after they finish, watching as the green seed clusters develop. The seeds are harvested green for pickling or green salsa applications, or allowed to turn beige-brown on the plant for drying.
Harvesting coriander seeds: Once seed heads begin to turn brown, cut the entire stem (before the seeds fall naturally) and hang upside down in a paper bag in a cool, dry, ventilated space. As the seeds dry further, they fall into the bag. Dry completely before storing in an airtight jar. Home-grown coriander seed stored whole retains full flavour for twelve to eighteen months. Toast lightly in a dry pan before grinding for the most intense, complex flavour.
Consistent Moisture Prevents Premature Bolting
Drought is the fastest bolt trigger for coriander. Any period of water stress — even a day or two of completely dry soil — signals to the plant that conditions are deteriorating and triggers immediate seed production. Keep soil consistently moist throughout the season. In containers, check and water daily in warm weather. A mulch over the soil surface retains moisture and keeps roots cool.
Cool-Season Specialist
Coriander thrives in the cool conditions of spring and early autumn — below 21°C consistently. Above 25°C, bolting accelerates substantially even in 'Slow Bolt' varieties. The best UK coriander leaf harvests come from March–May and August–October sowings. June and July sowings in full sun in hot weather are typically shorter-lived; use these for the leaf-to-seed bolt, then harvest seeds.
Self-Seeding for Next Year
Allow some late-season plants to set seed fully and drop seeds into the ground. Coriander self-seeds reliably in most UK garden conditions, producing an early spring crop without any sowing effort. The self-seeded seedlings emerge in cool spring weather and establish quickly — often providing the earliest leaf harvest of the season.
Edible Umbel Flowers
The delicate white umbel flowers of bolted coriander are fully edible, concentrated in coriander flavour, and make a professional-looking garnish. Scatter over curry, dal, salads, or grilled fish. They also attract beneficial insects — hoverflies, parasitic wasps, and bees all visit coriander flowers prolifically. A bolted plant allowed to flower is still a productive and ecologically valuable garden resident.
Why Transplanting Fails
The taproot disturbance bolting response is the reason supermarket "grow your own" pots of coriander almost always bolt within days of being planted out. The pot-confined roots experience sudden release and the environmental change simultaneously — both triggers for rapid bolting. Seed direct-sown into its permanent position develops a root system adapted to its exact conditions and bolts much more slowly.
Companion Planting Value
Flowering coriander is one of the most effective companion plants for attracting beneficial insects to the vegetable garden. Hoverflies and parasitic wasps attracted to the umbel flowers are among the most effective aphid predators available — a row of flowering coriander adjacent to brassicas, tomatoes, or peppers provides excellent biological aphid control through the summer months.
Sowing Calendar
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| 🌱 Sow outdoors |
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| 🌿 Harvest leaves |
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| 🌾 Seed harvest |
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Common Problems & Solutions
| Problem | Likely Cause | What to Do |
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| Bolts immediately after planting | Transplanted (not direct-sown); root disturbance | Only direct sow coriander — never transplant. Supermarket pot plants bolt rapidly because the root disturbance of re-potting or planting out triggers the bolting response immediately. Start from seed directly in the growing position. |
| Bolts within 2–3 weeks of germination | Too hot; drought stress; July or August sowing in full sun | Sow in a slightly shadier position in midsummer. Water consistently — never allow to dry out. Accept that midsummer sowings have a shorter leaf window; sow more frequently (every 2–3 weeks) rather than every 3–4 weeks in July–August. Use these plants primarily to reach the coriander seed harvest. |
| Seeds slow to germinate | Each "seed" is two seeds fused together — normal; soil too cold | Coriander germination is reliable from 10–14 days when soil is above 10°C. In March, warm the seed bed with a cloche for two weeks before sowing. The split-fruit structure is normal — expect two seedlings per sown seed and thin accordingly. |
| Sparse, thin plants | Overcrowding; insufficient moisture; poor soil | Thin to 5–10cm between plants. Keep consistently moist. Coriander benefits from slightly richer soil than many herbs — a light compost addition to the sowing area improves leaf density and productivity. |
Plant Specifications
One plant, two completely different harvests — the herb that keeps giving even after it bolts
Coriander rewards the gardener who understands its two personalities. Sow direct, a little at a time, every three to four weeks from March to September — never transplant, never let it dry out, and give summer sowings afternoon shade. Harvest the citrusy leaves through the cool months. And when it bolts, which it will, welcome the transition: let it flower for the beneficial insects, watch the seed heads ripen, and harvest the warm, nutty spice that tastes nothing like the leaves and is just as indispensable in the kitchen.
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