My soil only consist of two things, spangum peat moss and mushroom compost. Should I add some builders sand for better drainage? I guess I should have mentioned that the potatoes will be grown in smart pots. Going to be my first time growing potatoes. I can't find a soil recipe on the internet that works best for potatoes, so this year I mixed my own.
Depends on what the sand is. If it is soft sand (ie makes good sand castles) then no, it will just stick together and make a solid lump. If you mean sharp sand (rub it between your fingers and listen, you can hear it whisper) then yes it is ok to use. Really speaking you do need to add some loam (a soil with some clay in it) to your peat and mushroom compost mix. The clay acts as a 'sponge' holding nutrients and releasing them slowly for the plants to use.
