The start of June was very pleasant with mild temperatures and was certainly a great time to make a start on winter chores. There is always plenty to be done, starting with getting everything ready for the winter repotting schedule.
You should check your trees, deciduous species in particular, to see if repotting is required. Generally, such trees will require repotting every 2-5 years, depending on the vigour of the species and the age of the tree. Younger trees in the development stage usually require repotting more regularly and need to be shaped and styled more often, keeping in mind the eventual outcome you’re aiming for in future years. More mature trees usually don’t require as much wiring and root work, as their branches have been previously styled, and they have most likely already been in a bonsai pot for several years.
Some of the species you should be working on include crabapples, maples, elms, wisteria, liquidambars, flowering prunus of all types, deciduous conifers and ashes. Bear in mind that any trimming you do to the tops of flowering bonsai will reduce the quantity of flowers you have in spring. Any severe pruning of the top should wait until after flowering has finished. It’s fine to prune the roots, as long as you balance that with trimming back immediately after the spring flowering. Deciduous flowering trees (if healthy) should have plenty of energy in store to get them through the first few weeks of spring, even if they have been root pruned in the winter.
One of the first of the flowering ornamentals to burst its buds (around the same time as the flowering quinces) is Prunus mume (flowering apricot), so attend to these first if you have any in your collection. My ‘chojubai’ has already flowered in late June! Boston ivy and Virginia creeper are also likely to come into leaf fairly early in the season. If you have a number of deciduous trees to work on, watch carefully for the swelling of leaf or flower buds and prioritise accordingly. Once the flowers or first leaves have opened, it is too late to repot for the year, and you will need to wait until next year.
Winter is a great time to pot up any deciduous group or forest plantings you have planned for. Make sure that all the trees you use are identical in species and are similar in behavior (i.e. that they all lose/ don’t lose their leaves fully, all colour well in autumn etc.) or your group may not give you the year-round effect you want. A greater impact can be achieved with ‘starters’ by grouping them together in a tray with interesting rocks, pebbles, mosses and/ or grassy plants.
I usually repot many of my native trees (excluding figs) during July, as at this time of year they are less likely to suffer any setbacks, because of the cold weather. Most native species are likely to be pretty dormant now, but check the tree is not in active growth at the time of repotting. For example, in 2023 I was able to repot one of my sticky wattles in July but had to leave the other one because it was in active growth at that time. I normally try to focus on one species in a repotting session to ensure I don’t miss any! So far this season I have repotted a couple of my wisteria early, because one of them had persistent oxalis bulbs in among the roots that I wanted to try (yet again) to remove completely.
August is also a good time to work on some native species, before spring flowering and the associated flush of new growth. There are other times of the year when natives can be successfully root pruned, as most species have several brief periods of ‘dormancy’ during the normal growing season, when there is no active new growth and new leaf buds are starting to swell. I remember Lee Wilson, during one of his numerous demonstrations, saying that when native species are coming out of a dormant phase is the right time, but when they are going into a dormant period is not the best time, for successful root pruning. Naturally, our aim is always that our bonsai trees should survive and flourish after repotting.
Keep clearing up any wayward weeds and fallen leaves and continue vigilance with watering. Care needs to be taken not to over-water during winter, as this may lead to fungal root problems. Deciduous trees, in particular, are much slower to dry out while they are in their dormant phase, particularly if your bonsai mix has a high organic component. Be aware though, that any recently repotted trees will have a reduced root mass, so care needs to be taken not to allow them to completely dry out. Windy winter days will probably mean that watering needs to be more frequent than during calm weather, as wind can be very drying and stressful for tiny trees in little pots.
Check and remove or rewire any of your trees that have been wired during the growing season. Winter is also a good time to check the outline of deciduous trees, while leaves are not blocking your view, and trim back as appropriate. If possible, always make sure that you prune back to a spot just above a bud pointing in the direction where you want to see future growth.