Gadenin日本語Get the appWhy it works in a pot when other brassicas do not
Most brassicas need a long season and a deep root run, which is why cabbage and broccoli disappoint in containers. Komatsuna is finished in four to six weeks, roots mostly in the top six inches (15 cm), and never gets tall enough to blow over. It is the brassica that a balcony or a doorstep actually suits.
The container also solves the crop's main problem. Flea beetles and cabbage caterpillars find garden rows quickly, but a pot on a hard surface away from an existing brassica bed is a much harder target, and a single pot is trivially easy to cover with mesh compared with a whole row.
The one thing a pot cannot forgive is drying out. In open ground a komatsuna plant that gets dry recovers; in a pot the same check makes the leaves tough and the flavor sharply hotter, and it does not come back from it.
Choosing the container and filling it
Depth matters less than surface area, but there is a floor below which the crop cannot work. Anything shallower than four inches (10 cm) dries out faster than you can keep up with and will only ever give you baby leaf.
| Container | Minimum depth | What it will give you | How many plants |
|---|---|---|---|
| Seed tray or shallow trough | 4 in (10 cm) | One cut of baby leaf | Sown thickly, not thinned |
| Window box | 6 in (15 cm) | Medium leaves, cut and come again | One every 4 in (10 cm) |
| 10 in (25 cm) round pot | 8 in (20 cm) | Full-size plants with thick stalks | Three or four |
| Grow bag or large tub | 8 in (20 cm) | Full-size plants over several weeks | One every 6 in (15 cm) |
Use a peat-free multipurpose potting mix rather than garden soil. Garden soil compacts into a solid block in a pot within a fortnight of watering and the fine roots cannot get through it.
Filling, sowing and covering the pot
The sequence below takes a quarter of an hour and covers everything up to emergence. Do it in this order, because covering a pot after the seedlings are up traps whatever has already found them.
- Fill to an inch (2.5 cm) below the rim Leave that gap deliberately. It is the reservoir that lets you water properly in one go instead of trickling water on five times and wetting only the surface. Tap the pot down rather than pressing the mix hard.
- Water the mix before you sow Water until it runs from the drainage holes, then leave it for half an hour. Dry potting mix repels water and a seed sown into it can sit in a dry pocket for days while the surface looks wet.
- Sow and cover to half an inch (1 cm) Either scatter thinly over the whole surface for baby leaf, or make shallow drills 6 in (15 cm) apart for plants you will thin. Sieve dry mix over the top and press it down lightly with your palm.
- Put mesh over the pot straight away Three canes and a square of fine insect netting, or a cloche, tucked in under the rim. Leave it on until you harvest. Nothing about komatsuna needs pollinating, so there is no reason ever to take the cover off.
- Stand it where it gets half a day of direct sun Four to six hours is plenty. Full all day sun in high summer cooks a container and drives the plants to flower; a spot that is bright but shaded from mid afternoon gives better leaves in warm weather.
Watering and feeding a potted crop
Water when the top half inch (1 cm) of the mix is dry to your finger, and when you do, water until it runs out of the bottom. In warm weather that will be every day, sometimes twice; in cool weather it may be every third day. Judging by the surface alone is what kills container greens, because the surface dries in an hour while the root zone is still saturated. Lift the pot instead if you can; the weight tells you more than the look does.
A potting mix carries enough feed for about four weeks, which is roughly the length of the crop. If you are cutting and coming again beyond that, give a balanced liquid feed at half the label strength every ten days after the first cut. Komatsuna responds to nitrogen with soft broad leaves, but overfeeding gives you thin-walled leaves that aphids find first, so half strength is genuinely better than full.
Water at the base rather than over the leaves. Wet foliage sitting overnight in a still corner is how downy mildew starts, and a container on a sheltered balcony has far less air movement than an open bed.
In a container the flavor tracks the watering almost exactly. Evenly watered plants are mild and juicy; plants that dry out between waterings turn noticeably hotter and the stems get stringy.
Cutting a pot repeatedly
A container of komatsuna will give you two or three cuts if you cut correctly. Take the whole stand down to an inch (2.5 cm) above the mix with scissors, leaving the short stubs of the stems and the growing point intact. Do not pull the plants out and do not cut into the crown. New leaves push from those stubs and the second cut is ready in around two weeks in mild weather.
By the third cut the leaves come back narrower and hotter, and the plants are starting to think about flowering. That is the point to tip the pot out, refresh the mix and sow again rather than nursing it further. Keeping a note of the sowing date and the date of each cut on the pot itself is enough to tell you next season how many cuts your conditions really support.