In Sydney, this August has been unusually dry and warm, so we have had a pleasant start to spring, even if it feels as if it came a little early this year. Your deciduous trees will be coming into leaf (if they haven’t already) and you should have enjoyed some blossoms from such plants as prunus, crabapples and flowering quince. Hopefully, by now, you will have completed (or be close to finishing) repotting any conifers that need it.
As the new season’s growth commences on trees that have been dormant over winter, the work really begins. Pruning is so important in spring. If you have any cherries, apricots or quinces, prune, the foliage which develops very quickly after flowering finishes. This will increase branch development, as well as helping to keep your tree looking tidier.
Carefully watch the development of maples in general and Japanese maples in particular. As the second pair of leaves develops either pinch them off with your fingers, or use tweezers or scissors, when these leaves are quite small. If this practice is not done, long internodal growth (the spaces between leaves on a developing branch) will occur. An added advantage in doing this is that it also induces back budding along the branch. Maples tend to throw out two opposite shoots at a time along a branch, so you should select each time which shoots, if any, you want to allow to grow on for future development of your tree.
Most species of elm can be pruned back to two or four pairs of leaves to increase ramification. It is a good idea to allow six pairs of leaves to develop and cut back again to two or four leaves. Take more care though when pruning zelkova, as they resent being pruned back too hard and a trimmed stem may die back past the point you planned.
Spring pruning is not over yet, as evergreens are growing rapidly (especially privets) and conifers will need lots of attention. Remember that if there are any parts of a tree which are not developing well, you should not prune them until that section has become stronger.
Check any wiring on your trees carefully, as branch thickening during spring may lead to wires cutting in more quickly, leaving unsightly scars behind. It is generally better not to wire during spring for that reason, particularly with deciduous species. Remove wiring from a tree if the branch has set, or replace wire, spiraling in the opposite direction, if it has not yet set.
With so much active growth happening, it is time to start fertilising all your trees (except for recently re potted ones). Whether you liquid fertilise fortnightly at half strength or monthly at full strength, or every three months with a granular food, it doesn’t matter, but fertilise you must, if you want optimum growth and health of your trees. What is essential is that you follow the directions from the manufacturers and do not over fertilise.
Fertilisers high in nitrogen will induce a lot of new growth in your trees, but that is desirable in spring, particularly in younger trees. The trimming of excess growth where required (as mentioned earlier) is what will stop your trees’ trunks, branches and branchlets becoming too long for your liking during this growth spurt. Beware of using any fertilisers with a high phosphorus content on your native species, as too much of the nutrient can be toxic to many of them. I usually use a specific native food for most of the natives in my collection to avoid this problem.
As always, make sure your trees do not dry out. We have had several quite windy days lately, and it is in this type of situation that the growing medium is prone to quickly drying out. The particle size in bonsai mixes needs to be large, for good drainage and aeration of the roots, but for this reason also, frequent watering is essential. Trees in very active growth, particularly if they have been recently repotted, can suffer damage to their foliage or even die if moisture is not readily available. If one of your trees does dry out completely, it’s a good idea to immerse the entire pot in a tub of water, to just below the pot’s rim, until the bubbles stop rising (several minutes), to make sure that the entire root mass doesn’t become ‘water repellant’ and that future watering will get to where it’s needed.