April is usually the windiest month in Albuquerque. The average high temperature is 70 degrees, and the average low is 41 degrees. The record high is 89 degrees; the record low is 18 degrees. Humidity averages 30%. Start bringing trees out of the cold frame, but be prepared to put them back in should there be a late killing frost. Protect them from wind. Deciduous trees have probably started new shoots and/or blooms by now and need filtered sunlight. Do not expose any bonsai to full sun yet. Albuquerque sun is very intense due to the mile high elevation and mostly clear days. As spring and summer progress, temperatures get hot. Bonsai require an overhead light filter–a large tree, mesh lath work, etc. Set the trees on benches or tables, not on the ground. If they stay on the ground very long, they collect snails and pill bugs. The former eat leaves, and the latter eat the roots. Pill bugs will also get in the post when they are in the cold frame. After watering, soak entire tree and pot in a mild solution of fungicide and insecticide.
Watering: Don’t over water, but the winds are very drying. Deciduous trees need a bit more water than Juniper and pines. Generally, one watering a day in the morning is adequate unless the winds are up. By mid-afternoon ( 1-3 PM) they should be checked. Water the entire area; ground under the trees, walks, cover overhead, and surrounding garden plants to build up humidity in the air that the winds are drying out. DO NOT WATER a tree if it is in the full sun. Add MirAcid or a small amount of vinegar to your water barrel to neutralize alkaline tap water.
Fertilizing: Use all purpose fertilizer with nitrogen in mild solutions (2 to 1/3 amount called for in package instructions) or mild solutions of soil sulfur, iron tone, or MirAcid. Feed small amounts once or twice a month, not large doses every six months or so. Heavy concentrations of fertilizer can be toxic. See chapter on fertilizers on Naka’s Bonsai Techniques I.
Spraying: Spray for aphids. Mild detergents or insecticide soaps can be used. Protect soil with foil and wash off after treatment.
Trimming & Pruning: Toward the end of April, Flowering and fruiting trees will probably be in bloom. After 80% of buds have blossomed, remove all flowers and remaining buds. Berries may be left on. On fruiting trees, leave a few blossoms or there will be no fruit. See article on nipping and pruning in BCI magazine Jan/Feb 1988.
Repotting: If buds have appeared on deciduous trees, repot now before the leaves open and before the plant flowers. Evergreens can wait as long as the end of May. If repotted last year, they may not need it this year. This depends entirely on the growth pattern of the species. If tree is in bloom, do not disturb it. Deciduous trees are repotted first. In late April, pot trees that have wintered in the ground, but the same “budding” rules apply.
Grafting: In mid-April, use scions from the refrigerator. Late April–time to start cuttings and seeds under glass jars.