Towards the end of October the repotting of many of the other species of Bonsai is finished and in Sydney our next direction is towards the ficus species. The warm temperate varieties require consistent nightime temperatures not falling below 12 to 15 degrees for optimum results.
Results can differ if work is done prior to the above temperatures. This will depend on how drastic the pruning of roots and how much potting mix is removed. To rootprune out of season ie. when night temperatures are too cool: removing very little of the rootball is a waste of time. It is far better to wait and bare root. Figs can be treated as deciduous plants.
Pruning back branches to bare wood and the shortening of thicker primary roots will not kill figs, but the setback restricts their vigour. Figs repotted at a later stage are regrowing more vigorously than those repotted earlier.
The more tropical figs ie. F.macrophylla, F.benjamina sp. definitely respond to even warmer nights. Pruning during lower night temperatures can result in total or partial dieback of the branches so pruned.
The tip for autumn is to assess your bonsai, and any that are not vigorous enough or looking rather ‘sickly’ are better attended to rather than running the risk of losing them during the winter. Check whether the problem is the result of something else rather than a gluggy growing medium. However, if this is the reason, the first step to increased health will be to improve the potting mix. One that allows quicker draining and thus increasing the amount of air around the root system.
If it would be totally unsafe to remove the ‘soil’- poke a thick potting stick around the root ball in several places and wriggle it so that the base of the column is as wide as the top ( in other words, the hole should not be cone-shaped ). Fill these with a course sand or gravel to facilitate excess moisture to drain away which will be more healthy mix for the cold, non-growing months.
If a bonsai is in very bad condition, then more desperate methods are required to give the plant a better chance. Totally remove all the original mix and fill with sand/gravel and a small portion of humus. Do not remove any foliage at this stage, but in the chance of some photosynthesis being able to still take place, spray with some foliar fertiliser. If the plant survives, pruning and regular fertilising can proceed after the start of the growing season.
When considering repotting, it is important to work by the signs that the plant shows you, rather than the month. When the plant is showing signs of bud swelling, but before the leaf buds slit open, is the safest time to cut roots or disturb the root system.
This can be critically important to the repotting of Australian native trees (with the exception of figs). Being even more specific it is imperative that it be at the end of the dormant period, just prior to regrowth. Australian plants have the reputation of being tricky and not worthwhile transplanting. ….but….
Rootpruning keeps plants healthy, thus avoiding them from becoming stunted, a situation that depletes their vigour. This is at variance to conditions that should not be associated with our horticultural art.
Bonsai Koreshoff Nursery ©