Gadenin日本語Get the appThe sowing date decides which plant you get
Tatsoi grows two different-looking plants from the same seed, and which one you get is settled by the temperature it grows in rather than by anything you do later. Sown into cooling weather, it presses itself flat to the ground in a dark green disc of spoon-shaped leaves, so tight that a mature plant looks pressed under glass. Sown into warm weather, the same seed makes a loose, upright, open plant that stands eight inches (20 cm) tall with the leaves held on long pale stems.
The flat form is the one worth having. It is sweeter, denser, far hardier, and it is the plant that survives the winter. The upright form is perfectly edible but it is thinner in flavor, it bolts within weeks, and it never reaches the size the flat form does. So the practical instruction is simple: sow so that the plant matures in cold weather, not in warm.
That means the late summer and autumn window is the main sowing season, and a second short window in late winter as soon as the ground can be worked. A midsummer sowing germinates fine and disappoints you six weeks later.
| Soil temperature at sowing | Days to emerge | Plant you get |
|---|---|---|
| 40F (4C) | 8 to 12 | Slow, but flat and dense once it moves |
| 50F (10C) | 5 to 7 | Even stand, ideal for the flat rosette |
| 60F (15C) | 3 to 5 | Fast and reliable; still flattens as it cools |
| 70F (21C) | 3 | Upright and loose; short-lived |
| Above 80F (27C) | Erratic | Patchy germination, bolts young |
Depth, and why crusting matters more than usual
Sow a quarter of an inch (5 mm) deep, and no deeper than a half inch (12 mm). The seed is small and round and the seedling has almost no reserve to push through a hard cap. Tatsoi is sown mostly in autumn, which in many gardens means heavy rain onto bare soil within days of sowing, and a soil that caps will give you a stand with gaps you will be looking at all winter.
The fix is to cover the seed with something that will not set: sieved compost, leaf mold, or old potting mix, rather than the soil you scraped out of the drill. Water the drill before you sow rather than after, so the seed sits in damp soil under dry cover and you are not driving it deeper with a can.
If you are sowing into a bed that has just been cleared of a summer crop, rake the surface fine and firm it lightly with the back of the rake. Tatsoi seed sitting in a rough, airy surface dries out between waterings and comes up unevenly.
Spacing: give the rosette room to lie down
This is where most people go wrong with tatsoi, because they space it like a cutting salad and it is not one. A full-size flat rosette is nine to twelve inches (23 to 30 cm) across and it lies on the soil, so neighboring plants do not grow past each other the way upright greens do. They overlap, shade each other out from below, and trap wet leaf litter between them.
Decide before sowing whether you want full rosettes or baby leaf, because the two spacings are nowhere near each other. For full plants, aim for eight to ten inches (20 to 25 cm) each way. For baby leaf you can sow a thick band and shear it, but you are then growing a different crop and giving up the winter-hardy rosette entirely.
Sow two or three seeds per station at the final spacing and thin to the strongest, rather than drilling a continuous row and thinning most of it away. Tatsoi transplants well, so the thinnings are worth lifting carefully and moving to fill gaps.
| Growing style | Final spacing | First pick | What you get |
|---|---|---|---|
| Baby leaf band | 1 in (2.5 cm) | 21 to 28 days | Shear two or three times, then resow |
| Medium plants | 5 to 6 in (13 to 15 cm) | 35 to 45 days | Outer leaves picked individually |
| Full winter rosette | 8 to 10 in (20 to 25 cm) | 45 to 55 days | A flat disc you harvest whole or leaf by leaf |
Thin early, and thin for airflow underneath
Thinning tatsoi is not only about competition for light and food. Because the mature plant sits flat on the soil, crowded plants create a permanently damp, unventilated layer at ground level, and that layer is where rot starts in a wet autumn. Thinning is drainage as much as it is spacing.
- First pass at the first true leaf Seven to ten days after emergence, once the first true leaf shows past the round seed leaves. Reduce each station to two seedlings, snipping the surplus at soil level with scissors rather than pulling so you do not disturb the roots of the one you are keeping.
- Second pass at three or four true leaves Two to three weeks later, take each station down to one plant at final spacing. These thinnings are excellent eating whole, stem and all, and are milder at this size than the mature leaves will be.
- Firm and water afterwards Press the soil back around every plant you kept and water gently. A tatsoi left sitting in a loose air pocket after thinning checks for a week, and a checked plant in autumn may never make full size before the light goes.
Thinnings lifted with a little soil on the roots transplant readily if moved in cool, dull weather and watered in. Water them every day for the first week; they wilt flat and look finished, then stand up again.
Successional sowing, and what to write down
Sow a short row every two to three weeks through the cool part of the year rather than one large sowing. A row three feet (90 cm) long at full spacing carries four or five rosettes, which is enough for most households at each sowing, and overlapping rows mean the supply never breaks.
For every row, write down the sowing date, the position in the bed, and the spacing you used. Then add one more note when the plants mature: whether that row came out flat or upright. That single observation, tied to a sowing date, is the whole calendar. After two seasons you will know precisely the last date in your garden that a sowing still has time to flatten before winter, and that is a number no seed packet can give you.