Gadenin日本語Get the appWhy thinning matters more here than with most greens
Komatsuna puts on leaf area extremely fast. A row that looks comfortably spaced at the seed leaf stage is a solid mat two weeks later, and once the leaves overlap the plants stop competing for light in the ordinary way and start racing each other upward. The result is long thin leaf stalks, small blades, and plants that flop over on the first wet day.
Crowding also keeps the air still at soil level. Damp, stagnant air under a dense stand of brassica seedlings is what downy mildew and damping off need. Thinning is as much a disease measure as a growth one.
The habit to build is thinning little and often, three times, rather than once when you finally get round to it. Each thinning removes the weakest quarter of the stand and leaves the rest with room to use for another week.
The three thinnings and the spacing at each
Work by leaf stage rather than by days, since growth rate swings enormously with temperature. The stages below apply to a row sown for full-size plants. For baby leaf you skip thinning entirely and simply cut the whole stand at three to four inches (8 to 10 cm) tall.
| Stage | What the plants look like | Thin to | What you take out |
|---|---|---|---|
| First thinning | Seed leaves fully open, no true leaves yet | 1 in (2.5 cm) apart | Anything bent, pale, doubled up or lagging behind |
| Second thinning | Two true leaves showing | 2 to 3 in (5 to 8 cm) apart | Plants whose leaves already touch a neighbor |
| Third thinning | Four or five true leaves, about 4 in (10 cm) tall | 5 to 6 in (12 to 15 cm) apart | The smaller of each touching pair |
| No more after that | Plants standing clear of each other | Leave alone | Nothing; harvest whole plants instead |
If you only ever manage one thinning, make it the second one, at two true leaves. That is the point at which crowding starts to cost you leaf size permanently.
Pulling without disturbing the ones you keep
The risk with a seedling that fine is lifting the root of its neighbor along with it. Komatsuna roots knit together in the top inch (2.5 cm) of soil within a fortnight, so how you remove a plant matters.
- Water the row an hour before Damp soil releases roots instead of tearing them. Thinning a dry row on a hot afternoon leaves the survivors wilted for the rest of the day and sets them back more than the crowding did.
- Hold the soil down with two fingers Press either side of the plant you are keeping, then pull the unwanted seedling straight up with your other hand. Pulling at an angle levers the neighbor's root out of the ground.
- Cut rather than pull once there are true leaves From the second thinning onwards, snip the unwanted plant off at soil level with scissors instead. The remaining root rots away harmlessly and nothing else in the row is moved. This is also the safest option in a container, where everything is rooted into the same small volume.
- Firm the soil back and water Run a finger along the row to close any gaps you have opened, then water lightly. Seedlings left with their roots half exposed to air are the ones that stop growing while everything around them takes off.
- Clear the thinnings off the bed Do not leave the pulled seedlings lying between the rows. Wilting brassica leaves are exactly what flea beetles and slugs home in on, and they will move straight from the debris onto the plants you kept.
Every thinning is food
Komatsuna thinnings are not waste and they are not a consolation prize. At the seed leaf stage they are a mild sprout to scatter over anything. At two true leaves they are a salad leaf with a faint mustard edge. At four or five true leaves you are pulling small whole plants, root trimmed off, that cook in under a minute in a hot pan.
Rinse them in cold water immediately and use them the same day. They have almost no water reserve and go limp within a few hours in a warm kitchen. If you cannot use them at once, stand them upright in an inch (2.5 cm) of water in a jar in the fridge, the way you would treat cut herbs.
The mustard flavor is stronger in young thinnings than in the mature leaf, and stronger again in warm weather. If it is sharper than you want raw, thirty seconds in boiling water followed by a cold rinse takes the edge off without turning it to mush.
The final spacing is a decision about what you want to eat
There is no single correct spacing, only a trade-off. Thinned to three inches (8 cm) you get many small tender plants and the bed comes off in one cut. Thinned to six inches (15 cm) you get fewer plants with broad blades and thick pale stalks, and you can pick outer leaves from them repeatedly for weeks. In poor soil or a shallow container, err towards the wider spacing; crowded plants in a thin root run give you neither size nor quantity.
Note in your records how far apart you thinned each row and what the plants turned out like, alongside the sowing date and the season. Two or three seasons of that tells you your own garden's answer far more reliably than any spacing printed on a packet, because it accounts for your soil, your light and how you actually like to eat the crop.