Gadenin日本語Get the appA crop that is only as good as its speed
Bok choy has no storage phase. From germination to a full head is six to nine weeks of continuous growth, and quality is a direct function of how uninterrupted that growth was. The thick juicy white rib that is the point of the crop is built by water and nitrogen arriving steadily, not in bursts.
Nearly every problem below is a version of the same fault: the plant was checked. A dry week, a cold snap, a bed that ran out of nitrogen, or roots damaged at transplanting all produce the same set of symptoms, which is thin ribs, small heads, tough peppery leaves and a flower stem far too early. A check cannot be fixed afterwards, so the whole job is to avoid causing one.
Watering
Bok choy is shallow rooted, with most of its roots in the top six inches (15 cm), so it dries out before deeper crops in the same bed show any sign at all. Check by pushing a finger in to the second knuckle. If it comes out dry, water, whatever the calendar says.
Water heavily and less often rather than sprinkling daily. A soaking that wets the soil to eight inches (20 cm) pulls the roots down, while a daily splash keeps them in the top inch where they cook on the first hot afternoon. Water in the morning so the leaves are dry by evening, because wet foliage overnight is how downy mildew starts.
| Stage or weather | How often | How much |
|---|---|---|
| Sowing to emergence | Keep the surface damp daily | A fine spray only |
| Seedling to four true leaves | Every two or three days | Enough to wet 4 in (10 cm) down |
| Bulking up, mild weather | Every three to four days | Wet the soil 8 in (20 cm) down |
| Bulking up, above 82F (28C) | Daily, in the morning | Wet the soil 8 in (20 cm) down |
| Under mesh or a cloche | Check twice a week | Covers shed rain, so it is drier than it looks |
Midday wilting in hot weather that has recovered by evening is normal and is not a reason to water again. Wilting that is still there at first light is.
Feeding, and reading the leaf color
This is a nitrogen crop and a short one, so the feed has to be available now rather than released slowly across a season. Work well-rotted compost into the bed two to three weeks before sowing, then top up with a liquid feed while the plant is bulking.
Leaf color is the gauge. Mid to deep green with a glossy surface is right. Pale green with yellowing on the oldest outer leaves means the nitrogen has run out and the head will not fill. A very dark blue-green with soft floppy leaves means too much, and those are the plants that aphids and downy mildew take first.
| When | What to give | Why |
|---|---|---|
| Two to three weeks before sowing | Well-rotted compost dug in | Builds the base. Fresh manure causes root damage and mites |
| At two to three true leaves | Balanced liquid feed at half strength | Carries the plant through thinning |
| Two weeks before cutting | Balanced liquid feed at full strength | This is what fills the ribs |
| Within a week of cutting | Nothing at all | Late nitrogen ends up in the leaf as nitrate, not as quality |
Tip burn and bitter leaves
Brown papery edges on the young inner leaves are tip burn, and it is a calcium delivery problem rather than a shortage in the soil. Calcium moves in the transpiration stream, so it reaches the large outer leaves and not the small enclosed inner ones. It fails on hot days, in dry soil, and where a heavy nitrogen dose has pushed growth faster than water can supply it.
Bitterness has a different cause, which is heat and stress. Above about 82F (28C), or in a plant that has run dry, the leaves turn peppery and the ribs go stringy. Shade cloth over a summer sowing and consistent watering are the fix, and neither of them works retroactively on a crop that has already turned.
Cover it, and keep the cover on
Fine insect mesh over hoops from the day you sow is the single most effective thing you can do for bok choy. It excludes flea beetle, cabbage white butterflies, cabbage root fly and most aphids at once, and it costs almost nothing in light. Weigh the edges down into the soil, because flea beetles walk in under a loose edge.
The cover has to come off for thinning and weeding and go straight back on. A bed left open for one warm spring afternoon will have shot holes across every seedling by the next morning, and at the four-leaf stage that is most of the plant's leaf area gone.
Do not treat mesh as frost protection. It does not warm the bed. Use row cover for cold, and remember that row cover lying against the leaves in bright sun will scorch them.