Spring has most definitely sprung and this is the time when most growth happens on the trees in our bonsai collections. Watering should now be done daily, unless rain occurs. Check afterwards 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 by now. 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.
Weather can be changeable at this time of year, with hot days followed by slightly cooler conditions. As I write this, we have just experienced our second stormy afternoon, yesterday’s storm having included hail! Always check your trees for any damage after a storm, as torn leaves and branches may need attention. Soil may need to be replaced on the surfaces of some trees, where it has been washed off. Heavy hail may even break some of your pots, so try to avoid storing empty ones out in the open.
Trees in full leaf will require more water than those that are still dormant or just coming into bud. Protect trees such as azaleas, camellias, hornbeams and zelkovas from the sun as it becomes hotter, by moving them to semi shade. This will 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.
You may have some plants that have flowered earlier in the season, such as wisteria or azaleas, so don’t forget to remove spent flowers. Azalea flowers are particularly prone to petal blight in humid weather, so it’s best to throw any affected flowers into the bin 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 after flowering is finished (even during flowering) 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 December. 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.
Remember that spent flowers on fruiting varieties such a pyracanthas or cotoneasters should be left, because the fruit or berries will be forming.
Most of your 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 warm enough, and style them at the same time, removing any unwanted branches and long growth. Defoliation should be done in a couple of months’ time, but do not touch 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, add a small amount of garden lime to the soil by sprinkling it on top of your mix and then water 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. The recent showers of rain have meant that I already have fungal problems on one of my crepe myrtles, so I have cut back the new growth today and sprayed with eco fungicide.
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.