With the varying weather patterns in Sydney lately, our bonsai plants are either ahead or delayed in their growing cycles. This is only of concern if still needing to do late summer repotting or similarly, to be in a hurry to start autumn root pruning. At the moment following much needed extensive rainfall everything is vigorously growing. If this is the case in your area, there are many other things that can be done. You can guarantee that if the plants are growing well; so are the weeds.
It is surprising the amount of people encouraging: what we call star weed, an all invasive ground cover which others see as attractive. The problem is that it does look attractive but the roots become as a blanket, repelling moisture. As the tiny flowers and seed capsules appear, the cases spring open and a million (only a slight exaggeration) new plants quickly appear. Star weed (not unlike a fine rosette) can be removed by the fingers. If groups of seed come up it is almost impossible to pick them out. As long as you are careful it is possible to mix a small amount of Zero or Roundup (a herbicide) and with a child's fine paintbrush dab the weeds.
Marchantia (Liverwort), the flat fleshy plates of green, which is also an attractive surface, cover excludes both water and air from penetrating the potting mixture. This is due to the masses of fine hair- like rootlets. Conversely, it is a more difficult problem to eradicate. It is anchored to the surface by thread-like rhizoid like a suction cap. It is lifted or picked out using tweezers, the most minute sections can multiply growing and spreading quite quickly. Using vinegar with a small paintbrush will cause the prothallia (plates) to be reduced to brown jelly blobs. It looks unsightly for a while but later it can be removed.
The next stage begins with the refinement of foliage, (a prickly point). Just as new shoots begin to unfurl, all the foliage is cut away to a few mm. above the petiole. (the stalks are very short). This allows the stalks to heal at their base allowing photosynthesis to continue to create "sugars." The stubs eventually fall as energy deposits hasten to replace the "food factory". The structural "design" of your tree is this way revealed: when deciduous. With evergreens, foliage has to be physically removed. One can then better assess the quality of both form & outline & remove the unwanted. It is then wiser to trim the profile after- rather than before its shape is revealed. A big step toward quality refinement is by gradual elongation rather than a long sleek uninterrupted line.
The rain Sydney has been experiencing for many weeks now, will certainly be testing the quality of the draining capacity of your potting mixtures. Of the many questions I am asked, it is interesting how the varying conditions of the seasons, reflect the type of information that is requested. Due to the dry conditions of past years, the current problem didn't seem to occur. The problem? It is a dark slime that invades the surface of the potting mix.
The most common cause is from using fertiliser with high nitrogen: appearing on the surface. It is an indication of excess water & slow drainage. To alleviate this unsightly & unhealthy condition, is to change the mix. If it is unsafe to do so, then scrape away the top layer and wriggle a dowel, or a wide potting stick around, down to the bottom of the pot so that the base of the hole is as wide as the top, do not make a cone shape. Space several holes around the trunk and fill with gravel or coarse sand to aerate and drain away the clogged mix. This will be safer for the plant during winter, and at the correct repotting time improve the drainage.
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.
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