a top dressing of grit will help reduce moss but you just have to weed the other plants out. wind blown seed cant be stopped and any weed seed in the compost will grow. I reguarly weed my pots.

An inch or two of coarse mulch will help keep the weeds down, and make the few escapees easier to pull.

I agree with the above, a good mulch of grit or bark. But I can honestly say, I have never bought a bag of compost or gro bag for the past few years without one type of weed groing in each sack usually nettles. and I don't have nettle seeds inside my polyt.

Use the grit, as above, kepp the pots in the sun and don't get them too wet. This will reduce the amount of moss and weeds but nothing will eliminate them altogether.

Agree with the others, but would add one thing - if you've got moss/lichen on the top of all your pots, this often indicates the plant's been in the same pot too long and the drainage is now poor. Check they don't need repotting.

Or 'fiddle' around the plants with a hand fork to discourage it, A rolling stone...and all that!

thanks everyone for your advice