A little late but some of the following still holds true in January…. Many thanks to Amelia for compiling this and January’s task for us.
Winter is here and your deciduous trees should have a beautiful tracery as you can now see all the branches and twigs . While your evergreens may be starting to tone down their bright green or dark green foliage to a more dull tone. All your trees needing winter protection should now all being protected for the winter and here is a quick generic guide to bonsai in December as the colder weather has set into the UK.
Your bonsai trees will still need watering but not as often as their growth rate has slowed right down so the water uptake has also slowed down and the trees are in winter dormancy.
At this time of year if your trees are still outside, they will be getting watered naturally by the rainfall, morning dew and melting frosts. However, monitor the moisture level to ensure your bonsai trees are not water logged as this can cause roots to rot.
If your bonsai trees are under cover check daily and water if required to keep the soil damp / moist but not soaking wet.
Any bonsai being kept indoors should be watered regularly but this will have slowed down from a daily watering. They will be loosing moisture due to the higher temperatures inside drying out the soil and the tropical species still tend to grow during the winter period inside.
Ideal time to water is in the morning to allow the water time to dissipate and to reduce the surface water should the temperature cool down overnight or there is a frost.
If the weather is mild repotting can be undertaken but avoid early repotting if you have no protection for the tree like a cold frame or green house if frosts are likely.
Otherwise prepare for repotting by checking soil supplies and also that if you are looking to change the pot that you have the correct pot size to repot into.
Generally feeding in December is not required for either tree types as broadleaves trees are dormant and without leaves and conifers or evergreens have slowed down on growth during this period.
This is a great time of year to review your bonsai trees and check the structural image of the tree as well as the tracery and branch placement. Broadleaved trees are especially easy as they have for most species lost their leaves and are dormant. You can remove unwanted structural branches but remember to cover the wounds with wound paste or sealant as the trees are dormant and will not be able to respond to the pruning as effectively. Otherwise just mark the branch(es) to remove and wait till the Spring to then remove them.
This is not required to either broadleaved or coniferous trees in December. However, you may still need to trim the new shoots off tropical trees that are growing indoors to control the growth and develop ramification.
Carry out root pruning if you do start to re-pot now as part of the re-potting process and check for soil borne pests, root rot and other root problems and address if any issues are found. Given that the frosts have started though avoid repotting now until the spring.
Insects and pests
Continue to check your bonsai trees over fully for pests, insects and diseases as some insects can over winter on or in your trees like red spider mite, scale insect.
Pests are also likely if the weather is mild so worth checking to avoid disappointment in the spring when buds or leaves fail to flush due to pest attack. Typical pests still around include scale insect, mites, aphids and soil borne larva, vine weevil and beetles.
Moss and weed control
This should have been done in the previous months but check for any new moss forming.
Continue to check all your bonsai trees for health over the winter and review any that are not under protection in case of extreme cold weather or snow. If there is the chance of snow then make sure the branches do not get an excessive build up of snow that could cause them to break.
This is also a good time to photograph your bonsai trees and update their records for re-potting timings, feeding regimes, soil type etc as it is sometimes hard to keep track of what you do for each tree when you start increasing your collection. Keeping a photographic record does come in very useful over the years to see the trees development and your progress.