Spring has now sprung and hopefully all your bonsai trees have come through the winter. Here is a quick generic guide to bonsai in April but for individual species check out some of the other species-specific posts.
In the UK it has been a fairly dry winter so continue to check your trees daily and water as required but start to increase your watering with the buds now pushing and leaves opening. Water in the mornings ideally to avoid the colder temperatures at night. Spray any repotted trees to ensure they do not dry out.
You should now be coming to an end of your repotting so keep an eye on the trees your have repotted.
Review any trees that have yet to be repotted as it is a slow start to spring for some species so you could still repot in early April if it stays cool.
For any trees that you are not repotting still remove the top surface and re-top dress to remove any crusting on the surface to improve airflow and drainage down through the soil. Plus clean the pots of the trees if they have got green algae forming on them.
For broadleaved trees, start feeding any trees that are now out in leaf that you did not repot while do not feed those repotted in March yet, wait till the end of April. Start increasing the feeding of evergreen trees as they start to show more signs of stronger growth.
Tropical trees and Evergreens can continue to be fed with a low nitrogen feed to maintain health and vigor at the onset of spring.
Feed flowering trees that have not been repotted yet like Forsythia, Chamomiles, Cherry, Akebia etc.
Species to avoid pruning in Spring due to potential for sap bleeding would be Acer, Betula, Carpinus, Carya, Juglans, Magnolia, Morus, Populus and Tilia.
Remove unwanted branches and look for dead branches now that you can see the new buds swelling and clean out any dead branches before the leaves fully flush. Prune back any branches that are too long to a suitable live bud pointing in the right direction. Seal any large wounds with cut paste.
Now that the leaves are starting to appear trimming can be carried out to remove the terminal shoot in some species to aid with creating a more compact form. Continue to prune tropical trees to maintain their shape and trim the new shoots.
Where too much growth is expected and buds are well advanced, removal of unwanted future twigs may be anticipated by pinching out buds now. Where density is required of foliage, pinch or remove the terminal bud to promote side buds to develop. This is also a good opportunity to check buds to see if they are viable.
Species to avoid severe root pruning in Spring due to potential for sap bleeding would be Acer, Betula, Carpinus, Carya, Juglans, Magnolia, Morus, Populus and Tilia.
It is still worth checking the roots of trees that you are not fully repotting but this is more difficult if you have wired the trees into your pots as advised. If you are not seeing good bud swelling, then potentially there is an issue with the roots so remove from the pot and check for white root tips and healthy roots.
Insects and pests
Check for the newly emerging bugs and pests like green and black fly, red spider mite, scale insect, mealy bug as well as vine weevil beetles. With the onset of warmer weather insect pests can start to emerge and are more likely to appear on the new shoots and leaves.
Moss and weed control
Continue to keep this in check and treat or remove unwanted moss and remove any newly forming weeds.
Check wires and guys to ensure they are not cutting in and this is a good time to straighten out dis-used wire, which can be re-used for training wire.
Continue to protect from late frosts as it is still not very warm outside and ensure to harden off leaves before moving your trees out from a cold greenhouse.
Continue to update your bonsai records and photograph your trees to record their progress.
This is something everyone should do each time they use their tools but often it is not easy to do depending on how often you are using your tools. However, it is good practice to clean and sharpen your tools after use and this is a good time to go through your tool kits and clean them up before the start of the pruning season.
Subject to how you display your trees, if you are looking to bring your trees out later in Spring from their winter protection it is an ideal time to clean off your display areas or benches and disinfect them as well as re-treat with a wood preservative or relevant treatment for the material so they show your trees off once they are ready to come out.
If you have flowering trees, think about setting up a viewing of display area so you can admire these while they are in bloom and if you do bring them indoor ensure they remain in a cool room and only for a couple of days.
Take cuttings of late starters. Pot on last year’s seedlings. This is a good time to divide accent plants and split hosta’s if you haven’t already started as they are starting to emerge now.