Does anyone know anything about gardening?

Okay cool. Get one of those proper rainwater diverters so when your butt’s full the excess goes back down the pipe. Then it’s a case of getting some head, so either raise your butt above the pots or use a solar pump. For delivery you have a choice of seep hose, drip lines etc. For control, timer or moisture sensing probe.

I have only direct experience of the water butt part. But I am about to install a seep hose / timer setup in the polytunnel. It’ll start off mains fed but I intend to move to rainwater eventually.