Gadenin日本語Get the appWhat you are sowing, and why the season matters
Chinese milk vetch, Astragalus sinicus, is a small, sprawling legume from East Asia. In Japan and China it was for centuries sown into rice paddies after the harvest, where it grew through the winter, turned the fields pink with flowers in spring, and was then plowed in as a green manure before the next rice crop. That cycle is the one to copy in a garden: sow in autumn, let it sit through winter as a low rosette, enjoy the flowers in spring, and turn it into the soil afterward.
It is worth being candid about how it is grown in the US and UK. Here it is mostly used as a cover crop, a bee forage plant or part of a wildflower patch, not as an ornamental for a tidy border. The plants are low and floppy, and their value is in the soil improvement and the flowers en masse rather than in any single plant.
| Climate | When to sow | What to expect |
|---|---|---|
| Mild winters (much of California, the Gulf Coast, Texas, the Mediterranean) | Autumn, once the summer heat has broken | Overwinters as a rosette, flowers in spring |
| Cold winters (the Northeast, Midwest, Canada, much of the UK) | Early autumn for a trial, or early spring | Autumn sowings may not survive a hard winter; spring sowings flower later and less |
| Hot, humid summers | Autumn only | Plants die back as summer heat arrives |
Sowing step by step
The seed is small and is normally broadcast rather than sown in rows. Aim for an even scatter so the young plants knit into a mat before winter. Germination is best when the soil is moist and the weather has turned cool.
- Clear and loosen the ground Remove weeds and the remains of the summer crop, then rake the surface to a fine, crumbly tilth.
- Check the soil is not acidic Milk vetch does poorly in acid soil. If a soil test shows it is acidic, spread garden lime a few weeks before sowing.
- Inoculate the seed Where it has never grown before, coat the seed with the matching rhizobium inoculant just before sowing, keeping it out of direct sun.
- Broadcast thinly Mix the seed with dry sand to help spread it evenly, then scatter it in two passes at right angles to each other.
- Cover lightly and firm Rake it in to about a quarter to half an inch (0.5 to 1 cm) deep, then firm the surface with the back of the rake or by walking on a board.
- Water if the soil is dry Keep the surface moist until the seedlings are up; dry spells right after sowing are the most common cause of patchy stands.
Why inoculation helps
Like peas and clover, milk vetch fixes nitrogen from the air through root nodule bacteria. The catch is that it needs its own particular strain of rhizobium, which is not normally present in soil where the plant has never grown. Without it the plants still grow, but they form few nodules, stay pale and add far less nitrogen.
In Japan, seed sown in paddies with a long history of milk vetch rarely needs help. In a US or UK garden it almost always does, at least for the first sowing. Ask the seed supplier for the inoculant intended for Astragalus sinicus; inoculant sold for peas or clover is a different strain and may not work. Once a patch has grown well, the bacteria tend to persist in that soil for later sowings.
Sowing too early or too late
Sown while the weather is still hot, seedlings struggle and can be smothered by summer weeds. Sown so late that they go into winter as tiny seedlings, they are more easily heaved out of the ground by frost or killed outright by cold. The goal is a small, well-rooted rosette a few inches across by the time hard frosts begin.
Seed that is old or has been stored warm germinates poorly. Buy fresh seed for the season and sow it the same year.
Sowing into a vegetable bed
In a kitchen garden, milk vetch fits neatly into a bed that falls empty after the summer crops come out. Sow it over the whole bed as a winter cover, let it flower in spring, and turn it in a few weeks before the bed is needed for summer planting. It also works as an underplanting in an orchard or between fruit bushes, where its low growth keeps the soil covered without competing much for light.