I always love this time of year, because a lot of my trees have been repotted and/or restyled. I feel great satisfaction visualising the next step in development for each tree as I work on it. Some have been transferred from a training pot to a bonsai pot and some have been reshaped by wire or by pruning. Also, while all that is happening, the weed growth has finally slowed down, and I am almost on top of that constant chore (briefly, anyway).
We are starting to get some warmer days, although there are most likely some cold nights still to come. For this reason any newly trimmed or repotted trees need protection from the weather, particularly if fresh, soft new growth has started to appear. If any of your plants are showing signs of frost damage with burnt foliage, hold back on trimming it off until there is no chance of further frosts. The spoilt foliage, though unsightly, will help to protect the plant from any further damage. Once you remove the damage, the tree will revert to healthy new growth in spring.
Continue to keep a close eye on your watering, even though trees are not drying out quickly at the moment. August is frequently prone to cold, windy weather, which can reduce moisture levels in your bonsai pots very rapidly. Be wary of those warmer days ahead, which will mean you need to check daily whether your trees need a drink. Deeper pots are likely to dry out more quickly than shallow pots, as well, due to the way that the ‘water table’ within each pot operates. The moisture drains out of deep pots much more quickly. For this reason, trees in cascade pots may need to be watered more frequently than even the same species in a shallower pot. Any trees you have repotted during July should be showing signs of recovery, and/or new growth. With their recently reduced root mass, it’s particularly important not to let them dry out. Additionally, I normally water them over with Seasol once a week to aid their recovery, continuing to do so until I see new growth. Then it’s time to start fertilising too.
If you have not already done so, repotting of deciduous and flowering trees should happen now, as buds are already beginning to swell. In my collection, many have shot away very early this year. Once the buds have burst open, you will need to delay repotting until next year. Remember too that trident maples should be potted every year if possible, as they have very vigorous root systems. By the end of August elms and maples, which can shoot early, may need their first pruning back to 1 or 2 sets of leaves. Keep pruning any deciduous trees where any branches extend beyond the perimeter of the desired silhouette.
We can also begin to repot some evergreen trees such as privet, pyracantha, Buxus, olive or cotoneaster. Australian natives can be done at this time of year, but be careful as some are starting to put on a growth spurt already. July is often a safer time for repotting them (from my own experience). As with any other species, the ideal time to repot natives is just as the buds of new growth are starting to swell.
Whether you are repotting existing bonsai or creating new ones, it’s important to balance what you remove from the roots (percentage wise) with the foliage you remove from the top. You can get away with removing a little more foliage than roots, but the reverse does not work so well. The tree must always have sufficient roots in place to support the foliage on the top with water and also stability. If your trees are a bit unstable in their containers after repotting, it’s a good idea to wire them in place.
August is the best time to repot your pines. Remember that weak branches or those that you want to extend should not be cut back at this time. You can cut back elongated branches and remove unwanted branches on more vigorous parts of the tree, to balance any roots you remove during repotting. If you are well ahead with repotting you can also repot junipers, or wait with these until September.
August is also a good time to do aerial layers on garden stock or bonsai that have grown too tall. Try to do it just before the spring growth spurt, as the sap is rising then. If layering flowering plants, remove any flowers and buds as these will weaken the layer. Flowering plants will always expend energy trying to open flower buds if they are present. The drive to reproduce its kind is very strong! Make sure that any flowering layer does not flower for 12 months from the time the layer is done to preserve the energy for producing roots and leaves.
Search out and collect different types of moss to dress your trees, or use decorative pebbles on the soil surface after weeding, repotting or trimming. This way all your trees will reward you by looking their best.