How to Sow Kailan: Depth, Spacing, Soil Temperature and Thinning

Sow direct where the plant will stand

Kailan runs from seed to cutting stem in eight to ten weeks, which is too short a life to waste a week recovering from a transplant. Sow direct into the bed wherever the weather allows. A direct sown plant puts down a taproot straight away and pushes a thicker, juicier stem than a transplant of the same age, and thickness is the whole point of the crop.

Transplanting is still worth doing when the bed is occupied, when flea beetle pressure outdoors is severe, or when soil is still cold. In that case sow into 2 inch (5 cm) cells, one or two seeds per cell, and plant out at three to four true leaves, no later. A kailan seedling held in a cell past five leaves comes out with a coiled root and often throws a thin, hard stem that flowers early.

Cover the seed with a quarter to half an inch (0.5 to 1 cm) of fine soil and firm it down with the back of a rake. Seed sown deeper than an inch (2.5 cm) comes up patchy, and seed left sitting on a cloddy surface dries out between waterings.

1. Rake a fine, firm surface Break the top two inches (5 cm) down to crumbs and tread or tamp it level. Kailan seed is small and needs contact with damp soil, not air pockets between clods.
2. Draw a shallow drill and sow thickly Make a drill a quarter to half an inch (0.5 to 1 cm) deep and drop seed every inch (2.5 cm). Sowing thick and thinning later is far more reliable than sowing at final spacing and living with the gaps.
3. Cover, firm and water the drill, not the bed Backfill, press along the row with your palm, then water the drill itself with a fine rose. Watering the whole bed just grows weeds between the rows before the crop is up.

Soil temperature decides how fast it comes up

Kailan germinates over a wide band and, unlike most brassicas, it does not sulk at the warm end. It will come up at anything from 50F (10C) to 90F (32C), which is why it stays productive through a summer that stops broccoli and cauliflower dead. The practical floor is soil at 50F (10C); below that, seed sits and rots more often than it sprouts.

The speed matters because slow emergence is when flea beetle does its damage. A seedling that clears the soil in four days and puts on true leaves in ten shrugs off shot holes. A seedling that takes twelve days to appear in cold soil gets eaten flat. If the soil is marginal, warm the bed under a sheet of clear plastic for a week before sowing and lift it the moment the first seedlings show.

Measure soil temperature at sowing depth in the early morning, not at midday. The morning reading is the one the seed actually experiences for most of the day.

Spacing sets stem thickness, so choose it deliberately

Every inch you give a kailan plant goes into stem diameter. Crowded plants stretch upward and give a long, thin, whippy stem that cooks to nothing. Widely spaced plants give the thick, thumb-sized stem the crop is grown for, but you get fewer of them per bed. Decide which you want before you thin, because you cannot change your mind afterwards.

For the standard crop, thin to 6 inches (15 cm) apart in rows 12 inches (30 cm) apart. For thick, restaurant-style stems, go to 8 or 10 inches (20 to 25 cm) each way and feed accordingly. For a baby crop cut whole at pencil thickness, leave them at 3 inches (7.5 cm) and cut the lot over a fortnight rather than trying to grow them on.

Thin early, thin twice, and eat the thinnings

Thinning late is the most common way home growers ruin this crop. Kailan seedlings compete hard from the second true leaf onward, and a plant that spends a fortnight elbowing its neighbors never makes a thick stem no matter how well you feed it later. Thin the first time at the second true leaf and the second time about ten days after.

Do the thinning with scissors rather than by pulling. Pulling lifts the soil around the roots of the plants you are keeping, and a disturbed root at this stage shows up three weeks later as a stem that flowers small. Snip the surplus off at ground level and leave the root to rot in place.

The thinnings are the best salad leaf the plant will ever produce. Anything above about two inches (5 cm) tall is worth washing and eating raw, and it tastes cleaner and less bitter than the mature leaf. There is no reason to compost them.

1. First thin at the second true leaf Take the row down to one plant every 2 inches (5 cm). Remove anything pale, crooked, or noticeably behind its neighbors, and keep the stocky ones even if they are slightly closer together than ideal.
2. Second thin ten days later Go to the final spacing you chose, 3, 6, 8 or 10 inches (7.5 to 25 cm). Water the row afterwards to resettle the soil around the plants you kept.
3. Water the row after every thin A quarter of an inch (6 mm) of water over the row closes the small gaps left by the removed seedlings and stops the surviving roots drying out at the edges.

Sow again before the first sowing is ready

Kailan does not hold in the ground. Once the buds swell you have a window of a few days, and after that the stem is woody. That makes a single large sowing a mistake and a run of small sowings the right answer. Sow a short row every two to three weeks through the growing season and you get a continuous supply from one bed instead of a glut and then nothing.

The trigger for the next sowing is not the calendar but the previous row. When the row you sowed last is at four true leaves, sow the next one. In warm weather the intervals compress to a fortnight because the whole crop runs faster; in cool weather they stretch to three or four weeks.

What to write down at sowing

Note the sowing date, the soil temperature at sowing depth, and the final spacing you thinned to, along with which end of the row got which spacing if you tried more than one. Then note the date of the first cut. The gap between those two dates is the only number that actually helps you next year, and it varies more with your own soil and season than with anything printed on a packet.

Also record the position of each successional row. When you are cutting from row three and sowing row six, it is very easy to lose track of which row is which age, and rows sown three weeks apart look nearly identical for the first month.