Potatoes, Make the cut a sloping one to avoid water settling on the cut surface. Picture Gallery Cherry, This will ruin the structure of the tree and often leave jagged open wounds lower down. Never fertilize plum trees after July 1. You prune in summer to restrict the size of the plant and open up its interior (canopy). Spinach Use a safe set of steps / ladder to reach branches higher up. best applied in spring just before you spread mulch around the trees. A newly bought one year old plum tree planted in winter. and they are: