You should start to bring your bonsai out of their winter storage and place them on their benches. Sometimes you will find an excessive amount of moss. If moss covers the entire surface of the soil it will limit the flow of air and moisture to the root system and must be thinned. If moss is growing up the trunk of your bonsai it must be removed. Failure to remove moss on the trunk can be fatal.

Some bonsai experts clean the trunks of their bonsai in the spring. Take an old toothbrush (or borrow your spouse’s toothbrush), dip it in a mild soap solution, and gently scrub the trunks of your smooth barked trees. You will remove dirt, bugs, fungi, and moss and at the same time stimulate the tree.

Inspect each of your bonsai carefully and be especially alert for old wires. Remove all old wires. If old wires are not removed the bark can be permanently scarred because of the rapid growth of branches and the trunk in the spring. After you’ve removed the wire if the limb does not hold the desired position you will have to rewire the limb.

REPOTTING A bonsai is, by definition, confined to its container. At some point the tree will fill the container with roots and become "pot bound." Air, water and nutrients will not be able to penetrate the root ball of a "pot bound" bonsai. The tree will suffer and without some action being taken it will die. When should you repot? The answer depends on the age and species of tree, the size of the pot, and most importantly the health and vigor of the tree. But, as a rough guide, younger bonsai are usually repotted every one or two years and older trees less frequently.

Repot your deciduous trees first. The buds begin to swell anywhere from late February through April (at least in Cincinnati) depending on the species. As soon as these buds swell and just begin to open the roots should be pruned and the plant repotted. In general, maples are among the earliest to be repotted and oaks among the latest. This usually works out to somewhere between the first week of March and the first week of April. Deciduous spring flowering plants should usually be repotted immediately after flowering.

Hardy conifers have a wide range of appropriate pruning times and may be repotted up until June. Conifers are subject to root rot if their roots are pruned while still dormant. Pines can be root pruned any time after the candles begin to suddenly elongate. Junipers will tolerate late root pruning even into mid June.

Tropical trees should be root pruned only well after they are actively growing and the root temperature is above 60 degrees. I have successfully repotted a large ficus in the middle of July.

Protect newly repotted trees from the wind and direct sun for at least three weeks. Keep the soil moist but not wet. One month after repotting begin to fertilize weekly at one half the recommended strength. 

When repotting, let the soil become somewhat dry. If the soil is dry, it is easier to repot the tree and root damage is minimized. If you are potting a tree for the first time in a bonsai container it is a good idea to use a container that is somewhat large. The health and survival of the tree is improved if the tree is potted in a container larger than the size you ultimately want. The larger container has more soil which minimizes the shock from transplanting. When repotting, I use some Osmocote in my soil mix. Osmocote is a slow release fertilizer that releases its nutrients over a three month period.

WATERING Water your trees when the surface of the soil feels dry to the touch. Continue watering until the entire root ball is moist. Don’t water again until the soil surface feels dry again. Your soil should not be bone dry (complete absence of moisture) and is unhealthy for any tree even for junipers and pines (which prefer their soil to be somewhat dry). A moist soil is the safest and most desired condition for most plants. After moist, a soil becomes wet which can be tolerated by few trees. If your soil is always wet, check for poor drainage, non-functioning roots, and review your soil formulation.

COLD WEATHER If your bonsai are in leaf and we have a sudden cold snap you must provide your trees with protecting from frost. New growth is very tender. A sudden cold spell will not only kill the new growth but can damage new root growth.