Common Land Cress
Watercress in the UK

Right, so sowing watercress. You're looking at April, May, or June to get your seeds started. You can sow them direct outdoors, or if you've got a tray you can keep constantly wet, that's spot on too. Just sprinkle the tiny seeds thinly over some damp compost, don't bury them deep, just a light covering, maybe 5mm or so. They need constant moisture, like I say, so if you're growing in a tray, keep it topped up with water. You'll want to thin them out to about 10-15cm apart once they're big enough to handle. Remember, about 50 days from sowing to harvest, so succession sow every couple of weeks for a continuous supply right through to October.

Watercress loves its water, so if you're not growing it in a tray of water, make sure the soil is always damp. No pricking out or hardening off needed if you've sown direct outside, which is usually the way with this one. If you started them off in trays, just gently move them to their final spot, making sure they stay wet. Space them roughly 15cm apart, give them room to spread a bit. No need for any fancy support, just let them do their thing. They're not fussy about containers, as long as they get that constant drink.