Tatsoi
Pak Choi in the UK

You can sow pak choi direct outside from April right through to August, or start them off in modules on the windowsill or in the greenhouse. If you're sowing direct, make a shallow drill about 1.5 cm deep and pop your seeds in about 15-20 cm apart, then cover them over. If you're doing modules, put a couple of seeds in each cell, then thin out the weakest seedling once they've germinated. It's a quick grower, so don't be afraid to sow a few batches for a continuous supply. Sowing later in the season, like July or August, can help avoid it bolting in the longer, hotter days of mid-summer.

If you've started your pak choi in modules, you'll want to plant them out when they've got two or three proper leaves. Give them about 15-20 cm between each plant, like I say, and water them in well. Give them a few days outside to get used to the weather before planting them in their final spot, that's what we call hardening off. Some varieties are ace for containers too, if you're a bit short on space.