This summer, like last year, has been a lot cooler than normal and we have certainly had a lot of rain! I hope that you and your trees have survived both. Some of my trees appear to be suffering a bit from lack of sunlight, with too much elongated and rather weak growth. Hopefully, during autumn, the weather will be more favourable to them.
The days are still warm, so keep up with the watering and feeding, taking particular care if it’s windy. Keep an eye out, as always, for insect pests. Some may even be curled up in leaves, so hunt carefully. Try to only use insecticides when absolutely necessary as there may be beneficial creatures, such as praying mantises and ladybird larvae, searching for the insect pests we hate for their dinner! Also, it’s important not to spray any trees which are in flower, as this will be detrimental to foraging bees in the area.
Plants need to store energy as we approach winter. Use a low nitrogen organic fertiliser during autumn to harden late growth and improve flower and fruit production in spring. Remember to use a fertiliser low in phosphorus for your natives. Fertilising is also doubly important, as recent wet weather will have leached nutrients from the potting mix you are growing your trees in.
The foliage on your deciduous bonsai may have suffered during summer, but the trees are now trying to build up energy for the winter months, so try to get as much light as possible on them during the autumn months. Remove any dead leaves and check that the surface of the soil is free of dead foliage, as this may harbour fungal diseases. If the weather is not too hot, move trees like liquidambar, ginkgo, Chinese pistachio, Manchurian pear, some maples and zelkova into sunnier spots to improve their autumn colour. Shorter and cooler nights are the plants’ message to slow down, so as much sunshine as possible helps their colour. Autumn is also a good time to buy these plants when they are in colour, so you know what to expect in the future.
Tidy up figs by removing any overly large leaves,and cutting back any shoots that are too strong for the rest of the tree. Elms and other trees, particularly evergreens, that have thrown out long branches can be cut back to help develop ramification. Reduce the density of foliage as well, by selectively trimming off unwanted shoots and leaves. Check your trees for wire that may be cutting in, as branch girth may have increased recently. If branches have not yet set to where you want them, rewire if necessary. If there has been any cutting in, it’s a good idea to re wire in the opposite direction to the last time.
Don’t cut back deciduous flowering trees or plants such as azaleas and camellias, as you don’t want to remove the flower buds that are hopefully forming for next flowering season. I have spent time during the warmer month of February removing flowers and much lush foliage from the Bougainvilleas in my collection. They were badly in need of some attention, including repotting. The roots of these plants are very brittle and break very easily during the re potting process. Luckily, though, new roots grow back readily in summer, and they are also easy to strike from cuttings at the same time. It’s too late now (autumn) to work on such tropical species.
Prune pines, if you haven’t already done so, by removing candles once they are one to two centimetres long, unless you want to increase the length of that particular branch. Leave strong candles to develop on weak branches and weak candles to develop on strong branches. Some people even repot their pines in March, but I prefer to do mine in August.
Autumn is also a good time to start preparing your potting mix, as there will be plenty of use for it later in the season and during the winter months. I try to have plenty of the ingredients I use on hand for when I’ll need them. Lockdown, if nothing else, has taught me this!