September was an unusually dry month, with quite a few windy days, so hopefully you’ve all been able to manage the demands of your trees to keep them healthy and thriving. I repotted several natives and junipers in my collection last month, and it’s been challenging regularly spraying the foliage to increase humidity and prevent the trees dying from water stress. Some of my natives, in particular, dropped all or most of their leaves after repotting but I’m happy to say that new growth is now appearing.

After repotting any species, I usually keep the tree in a sheltered, shady spot for at least a couple of weeks, to allow it to recover from any shock. As well, I water weekly with Seasol during this time. At repotting time, I always reassess how suitable the pot is for the tree I’m working on and sometimes plant it in a new container. It’s interesting to see how different the tree can look after it’s planted in a new, more suitable pot.

Weather can be changeable at this time of year, with hot days followed by slightly cooler conditions. Recently repotted trees or those just coming into leaf may require misting (if possible) or more frequent watering to overcome the possibility of burning to tender spring foliage.

Spring is the time when most growth happens on the trees in our bonsai collections. Watering should now be done daily, unless rain occurs. Check that the soil is moist and the rain has penetrated the soil, as showers combined with wind may mean that you still need to water. As usual, inspect trees which are in full sun more carefully. It’s also important to fertilise your trees regularly from now on, as they should all be in active growth. Be sure to follow the directions for the use of whichever product you choose, and remember not to feed freshly repotted trees until they return to active growth.

Trees in full leaf will require more water than those that are still dormant or just coming into bud. Protect trees such as maples, ginkgo, azaleas, camellias, hornbeams and zelkovas from the sun as it becomes hotter, by moving them to semishade. This will also help prevent damage to their foliage.

Continue trimming back new growth to encourage short intermodal spaces, which will mean finer branching on your deciduous bonsai. Maples are notorious for requiring constant attention in spring. The normal practice at this time is to allow two or three sets of leaves to open on each branchlet, then prune back to the first new pair of leaves. Then where there were two leaves before, the tree will branch into four leaves, and so on. The exception to this pruning technique on maples is where you want a branch to lengthen or thicken to improve your overall design. In this case, allow the branch to grow unpruned for as long as appropriate. The more diligent you are at this time of year the better your tree will look in the future.

If you have plants that have flowered earlier in spring, such as wisteria or azaleas, don’t forget to remove spent flowers. However, spent flowers on fruiting varieties such a crabapples, pyracanthas or cotoneasters should be left, because the fruit or berries will be forming to give their display later in the year.

Azalea flowers are particularly prone to petal blight in humid weather, so it’s best to throw any effected flowers in the bin (not your compost) to avoid spreading the fungus. Infected flowers turn brown and wilt, so you should know what to look for. Azaleas with white flowers seem to be more prone to this problem, unfortunately. It’s now also time to watch out for azalea lace bug, which mottles the leaves on affected plants. Spray regularly with a systemic insecticide to keep them at bay during the growing season. Azaleas can be trimmed and repotted during or after flowering has finished but before the new growth begins. Be aware that the multiple ‘whorled’ shoots that come behind the spent flowers on azaleas must not all be allowed to grow. Choose one or two at each point that you want to keep for the design of the bonsai and remove the others.

Wisterias will begin to grow quite quickly now, so can be pruned back hard, as needed, until late December and you should get another flush of growth. You can even remove some of the leaflets from the compound leaves, leaving a couple of pairs of leaflets at the base of each, if desired, to make them look a bit tidier. Regularly remove any tendrils that the plants throw out, as you don’t want to allow the plant to climb everywhere, and are aiming for a more compact style. I tend to keep my wisterias out of the way over the growing season, but in full sun, because they can take up a lot of space, and potentially shade some of my other bonsai.

Most of your spring repotting should have been completed, but there is still time to work on junipers, serissa, cotoneasters, pyracanthas and, of course, figs.

Repot figs once the weather is reliably warm enough, and style them at the same time, removing any unwanted branches and long growth. Defoliation, if that is part of your practice, should be done in a couple of months’ time, but do not do this to any trees that are unhealthy, as these will not give the desired result. They will not have the strength to produce the new leaves and may be severely set back, or the plant could possibly die.

Olives and junipers can still be repotted. As these plants thrive in alkaline soil, you can add a small amount of garden lime to the soil by sprinkling it on top of your mix and then watering it in. This can be repeated two or three times a year as long as you do not overdo the amount of lime.

As all the insects are out in force now, use a systemic insecticide to prevent infestation of such pests as mealy bug, red spider, scale and aphids. Caterpillars like nothing better than tucking into juicy new foliage! They can be successfully treated with a biological control such as Dipel, which is very safe to use. Of course, manually removing insect pests when you see them is preferable to using any pesticides, but such diligence isn’t always possible or practical if you lead a busy life.

If doing any wiring at this time, don’t wire too tightly, as trees grow and thicken at an extremely rapid rate during spring, and it is easy to forget to check wire. This can result in scarring of the tree, which can take a long time to heal. If you do need to remove and redo wiring, it’s a good idea to then wire in the opposite direction to what you did the previous time.