Indeed cubes are a great tool. I use them for wormcastings. Osmocote is tricky since it floats, and will, if youre pulling stems out. I use lagunas plastic fert sticks since the cap comes off and theyre refillable. I use 19-6-12 osmocote. Buyer beware, there are several varieties of NPK ratings. I havent tested many but this one for sure works good.