Gadenin日本語Get the appA winter annual: sow before the cold, not after it
Crimson clover, Trifolium incarnatum, is a European native in the pea family, sold in Japan as strawberry candle for the shape and color of its flower spikes. It behaves as a winter annual. Seed germinates in the cool of autumn, the plant sits through winter as a low clump of soft, hairy leaves, and it pushes up its crimson spikes in late spring before finishing with the heat of summer.
That life cycle sets the sowing date. Where winters are mild, sow in early autumn so the young plants have time to establish before the cold arrives. Plants that go through winter flower most reliably, because crimson clover needs a spell of winter cold to trigger flowering. In cold-winter areas, where young plants are unlikely to survive, sow in spring as soon as the soil can be worked instead. Spring-sown plants grow well but may flower poorly or patchily, since they have missed most of the cold they need, so treat a spring sowing as a bonus rather than a sure thing.
| Climate | When to sow | What to expect |
|---|---|---|
| Mild winters, light frosts only | Early autumn, once the summer heat has eased | Plants overwinter small and flower well in late spring |
| Cold winters, ground freezes hard | Spring, as soon as the soil can be worked | Good leafy growth; flowering may be light or uneven |
| Hot summers, short spring | Early autumn where winters allow | Flowering finishes as summer heat arrives |
Sowing direct is easiest
Crimson clover is normally sown where it is to flower. It is grown by the field as a cover crop, and the same simple approach works in a bed or border: prepare a fine, weed-free surface, scatter or row the seed, cover it lightly and keep it moist until the seedlings are up. The seed is small, so a deep covering is the most common reason for a thin stand.
It can also be raised in small pots or cell trays if you want plants for a container or a particular spot. Sow a few seeds per cell, thin to the strongest, and plant out while the plants are still young.
- Prepare the bed Choose a sunny, well-drained spot and rake the soil to a fine, even surface. Remove weeds first, since young clover is easily smothered.
- Sow thinly Scatter the seed evenly over the surface or sow it in shallow drills. Sowing thinly saves a lot of thinning later.
- Cover lightly Rake the seed in gently or sprinkle a thin layer of fine soil over it, just enough to hide it, then firm the surface with the back of the rake.
- Keep it moist Water gently with a fine rose so the seed is not washed into clumps, and keep the surface from drying out until the seedlings appear.
- Thin to final spacing For a flower display, thin the seedlings in stages until they stand 8 to 12 inches (20 to 30 cm) apart.
No fertilizer needed at sowing
Like other clovers, crimson clover works with soil bacteria in its root nodules to fix nitrogen from the air. It needs little or no fertilizer, and extra nitrogen at sowing mostly feeds the weeds around it. Ordinary garden soil with reasonable drainage is enough. In ground where clovers have never grown, some gardeners use seed treated with a clover inoculant to help the nodules form, but it is not essential in most gardens.
Protect young seedlings from the first hard frosts
Established plants handle ordinary winter weather in mild areas, but very young seedlings are more tender. If a hard frost comes soon after an autumn sowing, a layer of row cover or a cloche over the bed gives them the light protection they need. This is another reason to sow early enough in autumn for the plants to make a few true leaves before winter.
If your autumn sowing is late and the seedlings are still tiny when frosts arrive, cover them on cold nights rather than resowing; a little protection usually carries them through.
Common sowing mistakes
The usual problems are sowing too deep, sowing too late in autumn so the seedlings meet winter undersized, and sowing in heavy, wet ground where young plants rot at the crown. In cold-winter gardens the other common disappointment is a spring sowing that grows into a lush green mat with few flowers. That is the plant missing its winter chill, not a fault in your care.