With the sun lower in the sky during the colder months, you may need to move your trees around to get more direct sunlight. Keep frost tender trees under protection if frosts are likely in your area.
To prevent your bonsai trees from having constantly cold, wet feet and damp foliage, it’s important to reduce watering for winter. Soil still needs to be kept moist, but only water in the morning, which gives time during the day for some drying out to take place. Unless the weather is very windy, the frequency of watering can be reduced during winter to every second or third day. In my collection the crepe myrtles and crabapples are my ‘sentinel’ trees, which wilt first to show me I need to water during summer. In winter this is more difficult to monitor, as dormant trees won’t give any such signals, and conifers won’t show the sad results of having been allowed to dry out until several weeks later.
Remove spent flowers and fallen leaves and keep soil surfaces and benches clean to allow adequate air movement and the sun to penetrate properly through the branches of your trees. This practice will also prevent the harbouring of pests and diseases in your collection. Clean out any dead brown needles on black and red pines to also allow the sun to filter through to all the branches and make the trees look tidier. This practice will apply to other conifers, for example junipers, as well. You can use tweezers for any hard-to-reach spots.
There are a lot of insect pests that are usually dormant, or die out completely, over the colder winter months, particularly in frosty areas. Insect life cycles are usually very short, and from March through to September there is a break in most of their attacks on our trees. This includes azalea lace bug, which is only around during the warmer months, although the mottling they leave behind on the leaves of affected plants might suggest otherwise. I have found that scale and their pesky relatives, such as mealy bug, can survive well over winter, though, particularly in sheltered areas, so it’s handy to have something like David Greys Systemic Bug Killer granules on hand. These are sprinkled onto the soil surface then watered in.
Clean out your toolbox and check for all the equipment (tools, wire, turntable etc.) in readiness for the deciduous repotting time which is creeping up on us. It’s a good time to start preparing your potting mixes as well. Once deciduous trees are dormant, they can be repotted, but unless your collection is very large it’s best to wait until July or even early August to start repotting. The first trees to break their dormancy will be such things as ornamental flowering quince and Virginia creeper, so repot these species first. In my collection, the Pin oak has the longest dormancy, regularly not coming into leaf until October. Thus, if I need to re pot that tree in a season, I leave it until last.
If you are interested in growing flowering trees like azaleas, camellias, flowering quince, bougainvillea, serissa etc. keep a look out for them at nurseries and other plant sales. These are best purchased when in flower, if possible, so you know what to expect in terms of colour and flower size. Remember that the smaller the flowers are, the more suitable the plant will be for use as a bonsai.