Gadenin日本語Get the appSpring: start as soon as the soil reaches 50F
Begin sowing as soon as the soil holds above 50F (10C), which is usually a couple of weeks before the last frost since young coriander takes light frost without harm. Sow a short row, then another every three weeks while the weather is still cool. Spring sowings are slower to reach cutting size than summer ones but give more cuts before they flower.
The main spring job after sowing is thinning. A crowded row in spring becomes a row that bolts together in early summer, because plants competing for water hit the drought trigger sooner. Thin in two passes to four inches (10 cm) apart, and mulch as soon as the second thinning is done.
- Check soil temperature, not the calendar Push a probe two inches (5 cm) down mid morning. Below 50F (10C) the seed sits and rots rather than germinating.
- Sow small and sow often A two foot (60 cm) row every three weeks. Sowing a whole packet at once gives you a glut and then nothing.
- Mulch before the weather turns Straw or leaf mold laid in mid spring keeps the roots cool into early summer and buys a week or two before the first bolt.
Summer: accept the gap or grow in shade
Once days run above 77F (25C) coriander will bolt within two or three weeks of germinating, and there is no variety choice or technique that changes that by much. Rather than fight it, plan for it. Sow only into afternoon shade, under a shade cloth, or in the shadow of a taller crop, and expect one cut from each sowing.
This is also the season to let plants flower deliberately. A row that bolts in early summer, left standing, gives you flowers for hoverflies through the worst of the aphid season and a seed harvest by late summer. It costs you nothing because that row was finished as a leaf crop anyway.
| Situation | Sow or not | What to expect |
|---|---|---|
| Open bed, full sun, above 86F (30C) | Do not sow | Bolts at four inches tall |
| Afternoon shade, mulched | Sow every 2 weeks | One good cut per sowing |
| Under 30 to 50 per cent shade cloth | Sow every 2 weeks | Two cuts if nights stay below 68F (20C) |
| Rows bolted in early summer | Leave them standing | Flowers for predators, seed by late summer |
| Containers on a hot patio | Move them, do not resow | Root temperature alone triggers the bolt |
If the summer gap is unacceptable, freeze leaf from the last big spring cutting. Two or three trays of frozen cubes will carry a household through six weeks of no fresh leaf.
Late summer and autumn: the best crop of the year
The sowings made as the peak heat breaks are the ones worth planning around. Cooling nights, shortening days and moist soil are exactly what coriander wants, and a plant sown then commonly stands in leaf for six to ten weeks and gives four to six cuts instead of two.
Sow every two to three weeks from the end of the hot spell until about six weeks before your first frost. Plants that are established before the cold arrives shrug off light frost, and under a cloche or in a cold frame they will keep giving through most of the cool season.
- Sow the moment nights drop below 68F (20C) That is the signal, not a date. Sowing a fortnight before the nights cool wastes the seed to a bolt.
- Sow the biggest row of the year This crop lasts. Where a spring row is two feet, make an autumn row four or five feet (1.5 m) and expect to keep cutting it.
- Have a cloche ready A simple low cloche or row cover thrown over the row at the first hard frost extends cutting by a month or more.
- Harvest the seed from summer plants now The rows you let flower in early summer will be turning tan brown. Cut them before they shatter.
Winter, and the year at a glance
In mild winters coriander sown in autumn simply sits, small and unbothered, and then grows away fast as soon as the soil warms, giving leaf a month before any spring sowing. Where winters are hard, an autumn sowing under cover or in a deep pot in a cool bright porch does the same job. The plants want cool, not warm: a heated room makes them stretch and bolt.
Taken as a whole the year has a simple shape, and it helps to see it in one piece rather than sowing by reflex.
| Season | Main job | What to check |
|---|---|---|
| Late winter to early spring | First sowing once soil is above 50F (10C) | Soil temperature at 2 in (5 cm) depth |
| Spring | Sow every 3 weeks, thin, mulch | Crowding in the row |
| Early summer | Last cuts, let a row flower | Feathery leaves in the crown |
| High summer | Shade sowings only, or pause | Night temperatures |
| Late summer | Restart sowing, harvest seed | Umbels turning tan brown |
| Autumn | The main leaf crop, sow generously | Six weeks left before first frost |
| Winter | Cloche the standing row, cut lightly | Slugs sheltering under the cover |
Keeping the record that makes next year easier
Coriander is the crop where a written record pays back fastest, because you sow it five or six times a year and every sowing is a repeat of the same experiment with different weather. Three dates per sowing are enough: the day you sowed, the day you first cut, and the day the flower stem appeared. Nothing else is needed.
After one full season those dates give you the two numbers you actually need. The gap between sowing and first cut tells you how far ahead to sow; the gap between first cut and bolting tells you how close together your sowings must be to avoid a gap. In most gardens the answer turns out to be closer than people expect, and the record is what proves it.
- Note where each sowing went Position matters as much as date with coriander, since the same seed sown in shade and in sun behaves like two different crops.
- Record the week the first bolt appeared Along with the highest temperature that week. That pairing is what tells you when to stop spring sowing next year.
- Note the autumn sowing date that worked The autumn crop is the valuable one and its window is narrow. Getting that single date right is worth more than everything else you record.