This year we have had another very windy October, with several showery days as well. All your trees should be in active spring growth by now. This will continue in the coming months, and one must be mindful of keeping vigorous trees trimmed to encourage short internodes and an improved design. Fast growing trees such as maples can be trimmed back to two leaves per branchlet, whilst less vigorous species to four leaves. Australian natives can be pruned relatively hard after flowering.
To keep your bonsai in healthy and active growth, regular fertilising is a must throughout the growing season. For the last few years, I have been using fertilisers branded ‘Troforte’, with good results. This is a controlled release granular product, which comes in a range of formulations for different types of plants. Included in their range is a general-purpose formulation that is suitable for most plants, even natives. You can use the little fertiliser baskets or empty tea bags with a product such as this, Seamungus, or a mix of your choosing. This means that gradual feeding takes place over time whenever your bonsai are watered. I used to regularly use soluble fertilisers only but find them very time consuming. Now I only use them occasionally and rely mainly on the gradual release types.
Fertilising on a regular basis is important because nutrients are leached out of the soil which is, by necessity, heavily watered. Some people fertilise a little and often but it all depends on how much time you can devote to this practice. It is important to emphasise that in times of high temperatures (above 30 degrees), DO NOT fertilise. Because the soil dries out very quickly in the heat, fertiliser becomes more concentrated in the soil during these times and may result in root and possibly even foliage damage (fertiliser burn). The use of slow-release fertilisers can help prevent this happening. Additionally, Seasol is always a good tonic to use when your trees may be feeling stressed, from recent repotting or very hot weather.
Continue to monitor candle growth on your black pines, which can vary considerably from tree to tree and even within the same tree. When many candles have elongated, pinch back to 3 to 5 mm. If more than one candle has developed on a branch leave two of similar growth and remove the rest. This will encourage future branching. Also, older needles can be thinned, particularly those facing straight up or down on a branch.
Other conifers can be trimmed back at this time to encourage back budding and denser foliage growth on branches. If you are cutting back conifers, junipers in particular, do not cut through the foliage, but rather behind a section, so that browning is minimised. I have just noticed my Podocarpus with new growth almost 30cm long in various places, so have given them a much-needed prune to shape.
Wisteria should now be in full sun and in water trays, as they are very thirsty plants. Keep pruning branches back to one or two leaves, as they are growing so rapidly. Always remove any twining shoots that the plant produces, as this is its natural habit as a climber. This is not the sort of growth that is desirable in your bonsai, however. Taxodium (Swamp Cyprus) is another species that will benefit from being placed in a water tray. They naturally grow in swampy areas, so will never suffer from over-watering. Tender plants, such as maples and ginkgo, should go into a more protected area so the leaves do not burn. Stop pruning crepe myrtle at the end of this month or they will not produce flowers.
Wiring can still be done, but try not to wire tightly, as the trees are still growing relatively strongly, and may suffer wire marks if not properly supervised.
We have had quite a bit of wind lately, even on the cooler days, so it’s important to regularly check that your trees aren’t drying out. Be diligent with watering and try to saturate the whole surface of the soil to encourage a wider and deeper spread of roots, therefore making the plant more drought tolerant. Try to avoid watering late in the day, as wet foliage overnight may encourage fungal diseases. However, it is a good idea to spray foliage in the morning to clean the leaves of dirt and pollution and discourage some pests. Check your plants for powdery mildew, which is a fungal disease. The trees prone to this are crepe myrtles, maples, crab apples and oaks. A way to avoid this is have plenty of space between your trees and to not water foliage late in the day.
Figs are in their element at this time of year, and you may start repotting, defoliating and pruning from now onwards, throughout the summer months. Large leaves can be cut off and new growth pinched out. When pruning figs, it is a good idea to spray the milky sap with water to prevent the sap leaving stains on the trunk and branches. Overgrown figs can be pruned back very hard, but it is a good idea to repot at the same time and add a good measure of slow-release fertiliser to your mix. They are very tough, and a healthy tree will respond very quickly to this treatment by producing a mass of new growth within a few weeks. Always ensure that the bonsai mix you are using is coarse and well drained, which helps prevent root problems such as rotting.
Be watchful for insect attacks on your trees, which can be a constant problem during the growing season. Treat azaleas regularly with a systemic insecticide through spring and summer to prevent lace bugs, which give the leaves an unsightly silvering effect once they are present. Maintain a watchful eye for other pests such as caterpillars, grasshoppers, scale and aphids. Keep your trees trimmed and tidy as much as possible, as this makes pests easier to spot. As I was weeding my trees last week (a constant challenge here), I was also dealing with plenty of green and some brown caterpillars in among the weeds. I was able to remove them by hand and mostly they hadn’t done much damage to my bonsai so far, but it’s a constant battle!
Weed free bonsai is a dream we all aspire to but rarely achieve, and weed growth is likely to be more vigorous through the growing season. Weeds rob your trees of nutrients and occupy valuable soil space in small pots, so it’s important to try and keep them under control, and especially don’t allow them to go to seed among your bonsai collection.
In my collection, I try to check each tree regularly, weeding and pruning at the same time. When I return a tree to its spot afterwards, I generally place it at least partially rotated from where it was, to try to keep the exposure to the light even for all sections of the foliage. This ensures that all parts of the tree receive a good amount of light to encourage balanced growth all over the whole plant. Remember that your trees need at least some attention from you every day.