May this year, has been a very wet month, like last year, I recall. This has significantly reduced the need to regularly water our bonsai but shouldn’t mean that we don’t pay them any attention at this time. A few of my deciduous trees are still green, as the rain has meant that nights haven’t been as cold as they would be without cloud cover, but I have noticed pleasing gold on a ginkgo and a trident maple outside as I write this.
The sun dips lower in the sky during the colder months, so you may need to move your trees around to get more direct light. My trees do not have ideal growing conditions, living as they do mainly on the north and western sides of our house. However, during winter I’m always thankful for the extra sunshine they can receive there. For me, summer is much more problematic light-wise. Of course, the ideal light for most of our bonsai is morning sun, with some, such as conifers, preferring good light all day if possible. It’s important to know the light requirements of the species of bonsai that you are growing and make appropriate adjustments based on your own growing environment.
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. The free draining mixes that are ideal for growing our trees should also help prevent waterlogging during such times. 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. During 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 to let the sunlight penetrate properly through the branches. This practice will also prevent the harbouring of pests and diseases in your collection. You should also clean out any dead brown needles on black and red pines to 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. June is a good time also to remove any moss that may have grown over roots and trunks of your trees. Use a soft toothbrush to gently lift it off without damaging the bark underneath.
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 April through to early 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. A lot of the trees in my collection are growing under cover, anyway, so some insect pests can remain active there over winter if I’m not watchful. I also have beehives in my garden, so need to be cautious about what I use on my trees, particularly flowering species. I only use pesticides if absolutely necessary.
Tidy up 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. Your tools may also need some attention such as cleaning, oiling and sharpening, although they are best maintained regularly whenever they are used.
It’s a good time to start preparing your potting mixes as well, as you are bound to be requiring plenty as winter progresses. Once a deciduous tree is dormant it can be re potted, but unless your collection is very large and thus due to time constraints, it’s best to wait until July or even early August to start the process. Personally, I feel a bit nervous about repotting my trees early in case they experience any die back afterwards. Once the sap is starting to rise (later in winter) and the leaf buds are beginning to swell, it’s very easy to spot the points to which you’d like to prune each branch. The first trees to break their dormancy will be such things as ornamental flowering quince, flowering apricot (Prunus mume) and Virginia creeper, so repot these species first.
If you have any camellias in your collection, these can be repotted immediately after flowering, before the new growth has commenced. You may be interested in buying flowering trees such as azaleas, camellias, ornamental quince, bougainvillea and Serissa, so 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. Although leaf size can be reduced over time with careful pruning of most species, flower and fruit size cannot be altered.
Don’t forget that at his time of the year, if you have any tender tropical species in your collection, you may need to move them to a protected area, to prevent frost damage as winter progresses.