You may have done all your winter bonsai tasks already but I have prepared a short list of some of those which I think are important and apply to most bonsai artists.
By now I am sure you all have done whatever pruning you wanted to do. Remember not to prune branches which are being used as sacrifices or that still need to thicken at the base. Pruning them would be counter-productive. It's also not a good idea to prune large branches in winter, assuming you are wanting back budding (buds which form further back along a branch or trunk which you can use in your design as future branches), its better to do this during the active growing periods. Pruning in winter when there is no sap flow is also not conducive to callousing over or healing of the resulting cut scars.
Weeds love this time of the year, at least in the Western Cape as we are a winter rainfall area. Be sure to weed as soon as these pesky plants begin to grow, or you might find they get out of hand before you know it. I find its a good idea to walk around with a bucket and throw the weeds into it as you go through your trees. Otherwise these weeds are thrown to the ground and simply grow there and seed, becoming an even worse problem.
Everyone loves moss, including myself. Moss makes the ideal bonsai tree ground cover. However if you live in a wet and cold area moss will proliferate and envelop the entire surface of the pot and will result in greatly increased water retention, which in turn may lead to root rot or other problems. Best is to keep moss to a minimum, at least for most of winter, allowing it to develop if you want, towards the end of the season. It is rather important though that you remove all moss from trunks, this will irreparably damage the bark, as it causes it to rot.
Its a good time of the year to collect moss though as there should be a lot about. Look in forests, along rivers or fountains, even along the roadside! Try to find different mosses which you combine around your trees for a little variety, as depicted in the image below.
Image caption. I think there is a perception that moss is grown year round on bonsai trees in Japan. In fact although there may well be some moss which has developed on a tree which has not been potted for a number of years, most of the times when you and I see moss on trees on exhibition, that moss has only days before been placed there.
Identify trees which need to be repotted in the coming season. A couple telltale signs of a tree which needs a repot:
Image caption. Some species need more frequent repotting than others. Chinese maples can fill a pot in a single season whereas most conifers need not be repotted for many years.
Don't simply repot because it sounds like the right thing to do, or because everyone is repotting and you feel left out. Repotting too frequently results in more bad than good.
Lime Sulphur is the one spray I highly recommended for applying in winter. It is ideal for preventing over wintering of common pests and fungi. It may be used on deciduous and evergreens bonsai trees. It is a highly effective fungicide solution which controls anthracnose (blackened growing tips affecting new leaves on deciduous trees especially maples), Mealy Bug, Mites, Powdery Mildew, Scale and Wooly aphids. Repeat application 2 weeks apart and use the entire bottle as it has a very short shelf life and cannot be stored once opened. You can use a dilution ratio of 1:10 (Lime sulphur:water)
Image caption. Lime sulphur is a very versatile spray to prevent the over-wintering of many pests and fungi.
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