This summer has not been particularly hot in Sydney. The humidity and the showery weather of late, has meant that I have had plenty of issues on my trees with such pests as scales of various types (white wax scale being the worst on some natives) and the usual caterpillars and fungal infections on susceptible trees. I’m sure I’m not alone though in facing these challenges! The weather is still likely to be warm in early autumn, so keep up with the watering and feeding, taking particular care if it’s windy.

Spacing your trees out to improve air circulation can help prevent some fungal diseases and also stop hungry insects from migrating to more of your bonsai. Try to remove insect s manually if the infestation is only small. 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.

Use a low nitrogen (preferably organic) fertiliser during autumn to help harden late growth and improve flower and fruit production in spring, because plants need to store energy as we approach winter. 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 inThe 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, maples and zelkova into sunnier spots to improve their autumn colour. Longer and cooler nights are the plants’ message to slow down, so as much sunshine as possible during the shorter days helps this process. Over this period the trees remove chlorophyll and nutrients from their leaves and into storage for the next growing season sealing off each leaf with a type of cork, until it eventually falls from the tree.

Autumn is also a good time to buy deciduous plants, so you know what autumn foliage tones 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. Night temperatures will be starting to drop below 16ºC, so it’s too late for repotting these tropical species. If you do get caught out, though, you may get away with it by moving recently repotted figs indoors each evening for 2-3 weeks in autumn, and positioning them in sunshine each day to recover. I have successfully used this strategy in the past for Ficus species that I missed repotting during summer.

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, re wire 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 usually spend time during the warmer month of February removing flowers and much lush foliage from the Bougainvillea in my collection. They are often neglected during the height of summer, because I have so many figs to attend to, and they are very forgiving. The roots of these plants are very brittle and break 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 though (autumn) to re pot 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. There’s nothing worse than planning a day of repotting and styling, only to find you first have to go and purchase the requirements you need to make this happen.