April has been a fairly dry month, with some windy weather to keep us all on our toes with our watering schedules. Just because the weather is cooler doesn’t mean we don’t need to be constantly aware of our little trees’ need for moisture. In their shallow pots, the media is like to dry out quickly, and lack of water is one of the most frequent reasons for losing precious trees, especially for beginners. Our bonsai need to be checked every day.
Keep your deciduous bonsai in full sun, if possible, at this time as this combined with cooler nights, should improve the colour intensity of autumn foliage. If you are in the market to purchase more deciduous species, this is a good time to look around, as you can see what autumn display any new trees are likely to give you each year. Trees are usually pretty consistent from year to year, either turning red, orange or golden before losing their leaves.
Make sure to regularly clean up any fallen leaves on the ground or soil surfaces, as these can harbour fungal disease and insect pests, which can negatively impact on your trees in the future. I usually have a lot of trouble with powdery mildew on my crepe myrtles during summer and early autumn, so those leaves, in particular, need to be cleaned up and thrown away. Remove old flowers and berries from trees, and move your tropical figs to more protected areas, if possible, under cover, so they are minimally impacted by the cold weather ahead, frosts in particular.
Check species, such as figs (particularly ‘Little Ruby’) and olives for insects such as scale and mealy bug, and treat appropriately with pest oil, or a systemic insecticide, if you find them. The presence of ants is a good indicator of a scale infestation, as they ‘farm’ the insects, collecting the secreted, sticky honeydew and even sometimes move the insects from one plant to another! Very annoying if your trees are kept close together like mine are. Remove as many of the pests as you can manually before you treat any infestation, as even once they are dead, the dried out ‘carcases’ still remain on the branches and leaves, so will need to be removed later anyway. These pests are normally most active in the warmer months, and some are able to breed and spread at an alarming rate. During the winter months, many insects are unable to survive the colder conditions, so aren’t likely to be a problem. If your trees are in a sheltered position (like many of mine are) some sucking and chewing insects can survive over the winter period unhindered, so always remain watchful. Just the other day I needed to remove a very hungry and well camouflaged caterpillar from one of my peach trees, and I only noticed it because I’d removed the tree from the bench for weeding.
Carefully remove any moss that has grown over the roots or up the trunks of your trees, trying not to damage the bark underneath. I use a soft toothbrush on some of my trees with smooth bark to solve this problem, but you have to be a lot more careful with species with rough or corky bark, so as not to do any damage to the beautiful bark which adds to the aged appearance of the tree. Persevere with the removal of weeds, as they seem to magically appear as soon as we get any rain. Weeds are a constant problem for me, as my collection is close to an untended block of land next door, with weed seeds very happy to migrate to the soil of my well-tended trees. I try to get the weeds out before they go to seed, as growing my own weed seeds only makes the problem worse!
Tree growth will generally be slowing down, so reduce the use of fertilisers, or use a weaker solution. Note that bonsai growing in an inorganic mix only have any fertiliser that you add to provide nutrients for growth, so will still need to be fed throughout the season. Seasol can be beneficial year-round as a tonic, especially after repotting or when trees are stressed in any other way. Some trees, such as many natives, will continue to grow in the cooler months while the deciduous species are dormant, so continue to shape and trim them as required. As the season progresses, all your trees will benefit from as much exposure to sunlight as possible, to build up energy to survive the winter months ahead.