Newbie - can someone tell me what this is?

we have a strange situation at ours. oh doesnt like onions (spring onions as well) in salads during week (she works). but we boys dont bother being smelly. the spring onions get expensive when you try to use in salads. and dont keep well in fridge by just having couple everyday.
I've devised an idea (not implemented it).
going to buy cheap value onions fill the litter tray with compost moist it and pack the onions in it. they can grow and we will cut and water it whenever needed and they can sit on window sill. a salad always on demand.
will that be a good idea (sorry to hijack the thread...)