Gadenin日本語Get the appPlant young, and plant on time
A Napa cabbage transplant should go out at three to four true leaves, roughly 18 to 22 days from sowing. At that stage the root ball holds together but the roots have not yet circled the cell, and the plant carries on growing without a pause. This crop has a short window and every day lost to transplant shock is a day taken off the head-filling period at the end.
A plant held to six or seven leaves in a small cell is already root bound. It will sit still for a week or more after planting, and it heads late and small even if everything afterwards is perfect. If your transplants have got ahead of the bed, plant them anyway rather than holding them further, and accept a smaller head. Napa cabbage does not recover from a hard check the way a headed cabbage sometimes does.
Plant in the evening or on an overcast day. A transplant set out at midday in late-summer heat wilts flat within an hour, and although it usually recovers overnight, that stall shows up in the head six weeks later.
Spacing decides head size
The head is made from the innermost leaves, but the energy to fill it comes from the wide outer rosette, which can spread 18 inches (45 cm) across before the head even starts. Crowd the plants and each one builds a smaller frame, so each head is lighter. Twelve to 18 inches (30 to 45 cm) between plants is the working range: use the wider end for a full-size autumn head and the closer end if you plan to cut some young.
Rows want 18 to 24 inches (45 to 60 cm) between them, mostly so you can get in to inspect the plants and lift the mesh. Airflow matters too. A block of Napa cabbage planted tight stays damp among the lower leaves in autumn, and that is exactly the condition slugs and soft rot want. If you have limited space, grow fewer plants at full spacing rather than more plants crammed in.
| Spacing | Typical head | When to use it |
|---|---|---|
| 10 to 12 inches (25 to 30 cm) | Small, one to two pounds (0.5 to 1 kg) | Fast types, or when you want to cut young and often |
| 14 to 16 inches (35 to 40 cm) | Standard, three to four pounds (1.5 to 2 kg) | The general-purpose autumn crop |
| 18 inches (45 cm) | Large, five pounds (2.5 kg) or more | Full-season types with rich soil and reliable water |
| Closer than 10 inches (25 cm) | Loose or unfilled | Not recommended for heading crops |
Soil: feed it before you plant, not after
Napa cabbage grows fast and it feeds heavily. Work two to three inches (5 to 8 cm) of well-rotted compost or manure into the top eight inches (20 cm) of the bed at least two weeks before planting, so it has settled and the nitrogen is available when the plant wants it. Fresh manure applied at planting encourages soft, sappy leaves that split and rot, and it draws aphids.
The bed should be near neutral, pH 6.0 to 6.8. Below about 5.8 this crop takes up calcium poorly, and poor calcium uptake is the direct cause of tip burn, the brown scorched leaf margins that show up inside the head where you cannot see them until you cut it. If your soil tests acid, lime it well ahead of the sowing, not at planting time, because lime takes months to act.
- Clear and compost two weeks ahead Pull the previous crop, spread compost and fork it into the top eight inches (20 cm). Two weeks of settling gives you an even bed rather than sinking pockets around each transplant.
- Check pH and lime early Aim for pH 6.0 to 6.8. If a test comes back lower, lime months ahead. Liming at planting will not raise calcium availability in time for this crop.
- Water the transplants an hour before lifting A well-watered root ball slides out of the cell intact. A dry one crumbles and half the fine roots tear away with it.
- Set the plant at the same depth it grew Bury the stem no deeper than it was in the cell. Napa cabbage buried to the seed leaves is prone to stem rot at the soil line in damp autumn weather.
- Water in generously, then mesh the bed Give each plant a pint or so (half a liter) to settle the soil around the roots, then close the insect mesh over hoops the same day.
The first two weeks in the ground
For the first fortnight the plant is building roots outward and it must not dry out. Late-summer soil loses water quickly, so check by pushing a finger two inches (5 cm) down rather than judging by the surface. Water deeply every two or three days in hot weather rather than sprinkling daily, which keeps the roots near the surface where they cook.
A mulch of straw or shredded leaves laid an inch or two (3 to 5 cm) deep once the plants have settled evens out the soil moisture and keeps the surface cooler. Keep it a couple of inches clear of each stem. Even moisture from this point on is the main defense against tip burn later, because the calcium the inner leaves need moves with water.
Rotation, and what to note
Napa cabbage is in the same family as cabbage, radish, turnip and mustard, and shares clubroot and root maggot with all of them. Leave three or four years between brassica crops on the same ground. If clubroot is already present, growing this crop there is not worth the effort, because a plant with galled roots cannot pull the water it needs during head filling.
Record the planting date, the spacing you used, and which bed each row went into. Adding the plant positions to a simple bed sketch pays off in two ways: it keeps the rotation honest, and when one end of the row heads better than the other, the sketch tells you whether it was shade, drainage or the compost that ran out halfway along.