It’s been a very challenging summer this year with poor air quality, reduced light on some days due to smoke and stricter water restrictions because of low dam levels. It’s important though, to try to maintain your bonsai as best you can, with hopefully better weather conditions ahead for us and our trees.
Watering is best done in the morning, as early as possible. Use a watering can with a fine rose to avoid disturbing the soil surface. If hot, windy weather is forecast, mist all foliage and the surrounding area of trees with a spray bottle to create a more humid environment. Immersing pots in water once a week can help keep plants in good condition. Adding a seaweed solution to the tub can give an added boost to stressed trees.
Small or shallow pots can be placed in trays filled with pebbles or sand to maintain humidity around them. Plants such as wisterias, swamp cypress, lilypillies, melaleucas and banksias should be sitting on pebbles in trays of shallow water as they are very thirsty species.
Keep your maples and other deciduous species sheltered from hot, dry winds, and preferably in shade to prevent burning of their leaves. Continue to fertilise your trees through the latter part of summer, but don’t do it on very hot days, to avoid burning the roots.
Any deciduous trees which have been defoliated earlier should have been placed in a shaded area until next month and then only exposed to sun when the temperature is not too high. The new set of leaves will be smaller and colour better in autumn, because they will have a higher concentration of sugars.
There is still time to repot figs and other tropical species but once the nights start to cool later in the month, it will be too late.
Black pine branches which have matured since forming in the spring may be cut back by up to half to encourage more compact budding. But do not cut back to where there are no needles.
Many trees have two growing patterns in a year: spring growth which gives new leaves and lengthens branches (high nitrogen), and the second spurt is autumn growth, which thickens the trunk (storing carbon). This latter spurt is the most important for bonsai growers, as it assists in giving an aged appearance to our trees. This is why using an organic fertiliser in the final months of summer is important to support this process.
Continue to shape branches throughout late summer (with the exception of any sacrifice branches which should be left to grow unchecked). Rotate your trees regularly so all sides get an equal amount of light, to promote even growth and prevent die back of weaker branches.
If we do get more rain, watch for any powdery mildew (appearing on crepe myrtles and oaks) and treat appropriately.