I love it when you get bonus veg or fruit. A few years back I sowed pak choi as a catch crop after something else. It didn't really come to much and some ran to seed. Each year since I've had a few small pak choi plants germinate in that same bed, from the seed, which has been nice.
This year, something has really got them going! The bed had early potatoes in which I dug up quite a few weeks ago. I then weeded the bed and planted out the leeks, under enviromesh. The pak choi has loved the disturbed soil and conditions under the mesh. Excellent!