Bonsai must be kept outside for most of the time – they are not indoor plants. They can be displayed indoors for two or three days only, every fortnight or so. Outdoors, a suitable place to keep your bonsai is on a deck or patio, or raised up off the ground on shelving. Make sure it is not easily knocked over by cats, dogs or strong winds. Shelter from direct sunlight for part of the day is also a good idea.
Under- or over-watering is the easiest way to kill a bonsai. During summer you will probably have to water the tree every single day, unless it rains heavily. Water with a gentle hose spray, or stand the tree in a bowl of water for about 15 minutes. Do not leave the tree standing in water for too long as it can cause the roots to rot and die. In winter you may only need to water the tree once a week or even less, but check the soil for moisture daily, anyway.
Bonsai need regular nutrients to stay healthy. Most balanced fertilisers (ie with roughly equal amounts of N-P-K) will be okay. Many people prefer to use an organic liquid fertiliser that can be applied with a watering can or by soaking the whole pot. Use liquid fertilisers once a week or fortnight during the growing season. Solid chemical fertilisers, such a long-acting pelleted fertiliser (similar to Osmocote) should only be applied once or twice during the growing season. Be careful not to over-fertilise with high concentrations as this can damage the roots of your bonsai.
Don’t prune the new growth off your bonsai right away. Let new shoots in spring grow out to five or six new leaves or pairs of leaves, then shorten back to leave three to four buds/ leaflets only (usually in early December sometime). Shorten the next set of new growth after the tree stops growing in late autumn. Every few years you can shorten each branch to keep the tree to the size you want.
The moss on the surface of your bonsai soil will naturally tend to die back during the summer, as it does not like the hot and dry weather. Don’t try to keep the moss alive by over-watering your bonsai, the moss will grow back naturally in Autumn. Or you can scrape some moss off a path or shady area and place it on your bonsai if you want it to look nice for visitors.
It can be helpful and healthy for your bonsai to mulch the soil surface with finely chopped sphagnum moss, pressed down into a compact ‘mat’, which will also help the ordinary green moss to grow.
Bonsai are very beautiful when displayed in a special place in the house for a special event (eg a birthday or anniversary or to show to a special friend or visitor). The Japanese traditionally set up a bonsai in a special display area with other objects such as a painting, a small plant or sculpture or antique object. Then they will sit with friends, drink tea and admire the bonsai display, sometimes with music playing to match the mood of the occasion.
We are not so formal, but it is still nice to show off your tree. If the bonsai is in the house for more than a day, use a sprayer to mist clean water over the tree and surface of the soil or moss. Try to place the tree somewhere where it gets good light, but doesn’t get too hot. Put the bonsai back outside after a day or two and water it well.
Remove any weeds or other plants that appear in the pot as soon as possible – they are stealing the water and fertilizer your bonsai needs to remain healthy
Pests and disease
Bonsai can suffer from the same pests and diseases that a full sized tree can get. It is okay to use most bug sprays on your bonsai (not weed killer!).
Your bonsai will need to have its roots pruned and fresh soil mix added on a regular basis to stay healthy. Repot about every third year. The person that you bought your bonsai from or a member of a bonsai club will often be able to do this for a small fee, if you don’t feel confident to do it yourself.
If you want to do it yourself it is not complicated, just make sure to use a soil with all-same-sized particles. For most species a mix of 2/3 of pumice and 1/3 coarse compost or coco-coir will be okay. Use a sieve to remove all the dust and very fine particles from the mix before you use it.