It has been a pleasant end to summer, with cooler nights and some good rain in recent weeks.
The days are still warm though, so keep up with the watering and feeding, taking particular care in windy weather. Use a low nitrogen organic fertiliser during autumn to harden late growth and improve flower and fruit production in spring, as plants need to store energy as we approach winter. Remember to use a fertilizer low in phosphorus for your natives.
The foliage on your deciduous bonsai may have suffered from the summer heat, 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. Remove any dead leaves and check that the surface of the soil is free of dead foliage, as this may harbour fungal disease.
If the weather is not too hot, move trees like liquidambar, gingko, Chinese pistachio, Manchurian pear, 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.
Keep an eye out for insect pests and use a systemic pesticide such as Confidor if necessary. If you have azaleas, you will need to continue to spray for lace bug right through March. These insects are not active during the cooler months to come.
Tidy up figs by removing any overly large leaves and cutting back any shoots that are too strong for the rest of the tree. It is too late now to repot or defoliate these species, so if you have missed any, you should wait until the warmer weather next spring. 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 rewire in the opposite direction to the last time, to help reduce the impact of the scarring and minimize the possibility of causing more damage.
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 spring. These species should not be cut back any later than early February.
Prune pines, if you haven’t already done so, by removing candles once they are one to two centimetres long. Leave strong candles to develop on weak branches and weak candles to develop on strong branches.
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.