Tatsoi is a low, cool-season Asian green with dark, glossy, spoon-shaped leaves on short pale stems. It grows in a neat flat rosette and has a mild, faintly mustardy flavor. You can pick baby leaves within a month and whole heads soon after. It is easy to grow if you give it cool weather, which makes it a good crop for spring and fall.
Sowing and planting
Tatsoi grows best when days are cool and not too long. Plan two main seasons: early spring and late summer into fall.
For a spring crop, sow outdoors two to four weeks before your last frost, as soon as the soil can be worked. For fall and winter crops, sow six to eight weeks before your first fall frost. In mild winters, such as USDA zones 8 to 10, you can keep sowing through fall and winter.
Sow seed 1/4 to 1/2 inch (6 to 12 mm) deep in rows 12 to 18 inches (30 to 45 cm) apart. Seedlings usually appear in four to seven days. Thin them to 6 inches (15 cm) for baby leaves or up to 12 inches (30 cm) for large rosettes. Eat the thinnings in salads.
You can start seed indoors three to four weeks before planting out. Use cell trays so the roots are not disturbed. Harden off the seedlings (get them used to outdoor conditions over a week) before planting. Set them out at the same depth they grew in the tray.
For a steady supply, make small sowings every two to three weeks while the weather stays cool. Stop sowing once summer heat arrives, then begin again as nights cool in late summer.
Tatsoi suits containers, window boxes and the edges of raised beds. A pot 6 to 8 inches (15 to 20 cm) deep holds a small cluster of plants.
Growing on
Keep the soil evenly moist. Dry soil makes the leaves tough and hot-tasting and pushes the plant to flower. Water at the base, ideally in the morning.
Tatsoi grows fast and needs a steady supply of nitrogen. Dig compost into the bed before sowing. If growth looks pale or slow, water with a diluted fish or seaweed feed every two weeks. Wear gloves when handling fertilizers and wash your hands afterwards.
A thin mulch of straw, shredded leaves or fine compost keeps the soil cool and moist. It also keeps grit off the low leaves, which saves washing in the kitchen.
Tatsoi needs no staking, pruning or pinching. Pull any weeds by hand while they are small, since the rosette sits close to the ground.
In cold weather, a row cover or cold frame lets you keep picking well after frost. Tatsoi is one of the hardiest Asian greens and often survives under cover through winter in USDA zones 6 and 7. In warm spring weather, a light shade cloth can delay bolting by a week or two.
For companions, tatsoi sits well among lettuce, spinach, onions and herbs such as dill. Avoid planting it where other cabbage-family crops grew the year before, to reduce pests and soil diseases.
Harvesting
Pick baby leaves when they are 2 to 4 inches (5 to 10 cm) long, usually three to four weeks after sowing. Take the outer leaves and leave the center to keep growing, or cut the whole plant 1 inch (2.5 cm) above the soil. A cut plant often regrows for a second picking in cool weather.
For full-size rosettes, wait until the plant spreads 8 to 12 inches (20 to 30 cm) across. Cut the whole head at soil level with a sharp knife.
Harvest before plants start to bolt. A thickening stalk rising from the center tells you flowering is on the way. Leaves turn bitter soon after. Light frost sweetens the flavor, so fall crops often taste best.
Rinse the leaves well, shake them dry and store them in a bag in the fridge. They keep for about a week. Use them raw in salads or add them to stir-fries, soups and noodle dishes at the last minute.
Saving seed is possible but not simple. Tatsoi crosses readily with other Brassica rapa crops such as turnips, pak choi and Chinese cabbage. For true seed, let only one of these flower at a time.
Problems and pests
Tatsoi bolts (runs to flower) quickly in heat and long days. Sow early in spring or wait for cooler weather in late summer, and keep the soil moist.
Many tiny round holes in the leaves
Flea beetles, small jumping beetles that feed on young cabbage-family plants. Cover the crop with a fine row cover from sowing, sealing the edges with soil. Keep seedlings well watered; fast-growing plants shrug off light damage.
Large ragged holes and green droppings
Caterpillars such as imported cabbageworm, the larva of the white cabbage butterfly. Check under the leaves and pick off caterpillars and eggs. Row covers keep the butterflies off. Bacillus thuringiensis (Bt), a biological spray, controls caterpillars; follow the label and wear gloves when mixing.
Irregular holes and slime trails, worst after rain
Slugs and snails. Hand-pick them at dusk and use beer traps. Iron phosphate pellets are among the safer baits around pets; follow the label and store them out of reach of children.
Clusters of gray or green insects under leaves
Aphids. Knock them off with a strong jet of water. For heavy infestations, spray insecticidal soap in the evening, wearing gloves and eye protection as the label directs.
Plants flower before they fill out
Bolting from heat, long days or a dry spell. Pull bolted plants and sow again once the weather cools. Choose a shady spot for late spring sowings.
Varieties worth growing
Few named tatsoi varieties are widely sold. Most seed is sold simply as tatsoi, and close relatives fill the same role in the kitchen.
- Tatsoi (also sold as 'Tah Tsai' or rosette pak choi): The standard flat rosette type, very hardy and ideal for baby leaves.
- 'Yukina Savoy': A closely related, more upright green with crinkled dark leaves and good cold tolerance.
- Komatsuna (mustard spinach): A related Brassica rapa green, taller and quicker to bulk up, useful in the same beds.
- Mizuna: A related Asian green with feathery leaves that mixes well with tatsoi in salad sowings.