I would suggest two tablespoon for each cubic foot of potting soil you mix up. I like to use a bit of extra fertilizer for potted plants if they are annuals or roses as both are heavy feeders. Indoor plants that do not bloom and trees and shrubs require less fertilizer so one tablespoon per cubic foot of soil would be right for them. Keep in mind that the Osmocote releases the nutrients slowly as the plants need it so as the soil warms up in the summer they will get more nutrients just when they require it. Keep growing, Marianne Binetti