While the weather remains warm, it’s a good time to repot many species, particularly evergreens like pyracantha, cotoneasters, olives and star jasmine etc. Most can also be repotted in early spring, but I prefer autumn, as the daytime temperatures are usually more stable. Recently repotted trees will need protection if the nights suddenly become cold within the first couple of weeks after repotting.
It’s a good idea to tidy up conifers as well. Remove any dead or overly dense foliage on junipers and reduce the needles on species such as pines or cedars, by removing any that are on the undersides of branches. Remove unwanted candles as well on pines, leaving no more than two at any junction.
It’s now too late to prune back figs and they should be left until the warmer spring weather returns later in the year. While the weather is still warm maximize the amount of sunlight they receive but if the nights suddenly become cold move to a more sheltered spot. A lot of the fig species we use in bonsai are native to tropical areas, so can be set back or even severely damaged when the colder nights return later in the season.
Keep fertilising to build up strength for your trees to handle the colder months ahead. Keep using low nitrogen food to prevent a rush of soft new growth as this may be damaged over winter. Feeding of deciduous species in autumn is particularly important, to maintain health in the tree over the winter dormancy. Sunny days and cool dry nights will hopefully enable maples and liquidambars to show a lovely display of autumn colour before the leaves fall.
Autumn is a good time to do any wiring on trees, as the tree’s growth is generally slower over autumn/winter and the wire can be safely left in place for longer. Wiring done in spring, on the other hand, needs to be constantly checked as unsightly cutting in can happen alarmingly quickly.
Watering can most likely be reduced at this time, as the heat of the sun has eased off somewhat, but be alert nonetheless, particularly if it suddenly becomes windy. It’s still important not to allow your trees to dry out.
Last but not least, keep up with the weeding! Remember it’s your trees you want to nurture, not the weeds.