SPRING CARE: FERTILIZING. (April, 2011)
Organic fertilizer cakes made from rape seed or cotton seed meal (store-purchased or home-made) work well. Time-release fertilizers (i.e. Osmocote) can be used to supplement organic fertilizers. Wait at least four weeks after repotting bonsai before fertilizing them.
For mature deciduous trees, wait until new leaves harden before fertilizing lightly. If you fertilize too early, or too much, both leaves and internodes grow large.
For the tree in training, your goal is to make thick trunk. Fertilize your tree early. Big leaves and long needles help the trunk to grow large.
Feed Japanese Black Pines heavily in spring to help the trees bud after decandling. For a twelve inch long pot, start with four to six fertilizer cakes and add a few more every few weeks. When the surface starts to get full, remove old cakes and replace them with new ones. By the end of May, the surface of the pot should be covered with fertilizer.
Begin feeding white pines lightly when the new needles open, usually in May. Apply a light to moderate amount of fertilizer through fall, starting with 4 cakes for a large tree and adding 4 more a month later.