Outdoor: This is the busiest month in bonsai.
Once the danger of temperatures in the low twenties or less has passed, it is time to bring your trees out of winter protection and into their summer homes. For trees in mulch beds, be sure that the mulch has thawed below the pots before lifting the trees out of it. Do not force trees from a frozen mulch bed, as significant damage can result.
Watering requirements will increase, so be prepared to water more frequently. Fertilization can begin as soon as new growth begins. Lower nitrogen types will help maintain smaller foliage sizes. Only fertilize newly potted trees about 3 or 4 weeks after the repotting. Use a product like Dyna-Gro K-L-N at repotting to aid in root development.
Remove any wire that may become tight during the spring growing season. Replace the wire more loosely if needed. Wire deciduous trees before the appearance of new foliage. Repot trees as they come out of dormancy—usually, pines, larches, and spruces first, then deciduous trees and junipers. Reused pots need a thorough cleaning before potting. Pinch off a portion of each new growth on spruces before it hardens. Candle prune pines if new growth is sufficiently developed. Also, pinch back new growth on junipers and deciduous trees. Do not prune spring flowering (apple, azalea, etc.) and “bleeders” (maple, birch) at this time.
Indoor: Watering needs may increase as light intensity and day length increase. Fertilize as needed. Pinch back overly long growth. Wait to move these trees outdoors. Do not repot at this time. Check wires and remove any that may become tight during spring growth. Replace wires as needed.
(from Bonsai Hai, April 2010)
