Over the past 25 years of running the Bonsai Shop in Dublin, I have come across many questions from beginners. The following is a selection of some of them with answers.
How do you take care of them?
The most important thing is watering. Bonsai need more watering than an ordinary house plant because they are in a much smaller container, and dry out faster.
Keep them near a window, if indoor , but not in strong sun.
Spray the leaves if trees are in a very warm atmosphere, in central heating, or in very hot summer weather. Alternately, keep the on a tray of moist pebbles.
Give them some fertiliser every two weeks from Feb. to Sept. and once a month in winter.
Prune them into shape now and then.. Tight at the top, loose at the sides. More details later.
Repot them every 2 to 3 years into a larger pot when they grow too big for their existing pot.
How do you water them?
First feel the soil. If it is wet your tree does not need to be watered. Water when the surface of the soil is beginning to get dry, but never let the soil of your tree dry out completely.
Fill up a sink or basin with room temp. water, ( use rain water, or filtered if possible) and immerse tree in water to base of trunk. Leave for 2 to 3 minutes or more, if tree very dry. Take out carefully, so soil is not washed away, and let drain. Return to its’ usual position near the window. Alternately if you use a sprayer to water your tree, make sure you spray enough water so that you see water coming out the drainage holes at the bottom of the pot.
Very large trees can be placed in a shower or bath and sprayed enough so the water can be seen running out of drainage holes as above.. This can also be done outdoors with a watering can for outdoor trees.
How do you shape them?
Most bonsai will have their correct shape when bought, so it is just a matter of keeping the tree in that shape. Prune it tight at the top, loose at the sides, in a pyramid rather than a lollipop shape. Generally, trim it back to the first set of leaves at the top, and to the second or third set at the sides.( Will be covered in more detail later.)
Remove any suckers at the base of the trunk, as they will take away from the shape and vigour of the tree.
How big do they grow?
You can decide that. If you want them to get larger faster just don’t trim them back as much and re-pot them into a larger pot more often. If you want them small, trim hard and often and do not re-pot so often.
The leaves on my tree have turned yellow and are falling off. What’s the cause of this?
If your tree in an outdoor deciduous tree ie. maples, beech, oak etc. they will shed their leaves in the autumn so this is natural, so don’t worry, they will return in the spring. With the evergreen types you may have a problem.
- Bonsai, being trees, do not like to be moved. If you have just bought one, it will take a week for it to adapt to its’ new environment. Do expect your tree to shed up to 50% of its leaves, when first bought or after it has been re-potted. It should start to put out new leaves and stop shedding after 2 to 3 weeks.
- Another reason for this can be letting the soil get too dry in between watering, or the soil was left very dry for several days ie, if you were away on holidays. This can cause severe damage to the tree and they will die if left too long without water.
- This problem is made worse if the tree is left in strong sun. Indoor bonsai should only be left in early morning or evening sun from March to September. But the more light and sun they get in the winter the better. Most of the outdoor trees will also not tolerate hot mid-day summer sun, so give them shade or position them in morning or evening sun.
- The other reason for leaf fall can be too hot and dry an atmosphere. Keep away from heaters, fireplaces, top of TVs and cookers. They like a cool, moist position. Keep on a tray of moist pebbles if the room is very warm.
- The last reason can be lack of light. Make sure your tree is no more than 3 ft from a bright window. If all your windows are very sunny, move it back enough so it is not in the sun through the summer months. If window has no sun, keep on window sill.
Can I keep my tree under a lamp as my office has no natural light?
Afraid not. Artificial light is like being in the dark for plants. They have to have natural light. There are special growing lights you can buy, but they are expensive.
Can I keep my tree in a conservatory?
A conservatory with temp. between 10 and 20 degrees is ideal in winter for most indoor bonsai, but is usually too hot in summer. Outdoor trees can be kept in a cold conservatory in very cold weather, but put them out again as soon as the weather turns mild.
Can I keep an outdoor tree indoors?
Yes, for short periods but not permanently. Deciduous tree need the change of seasons to know what to do .They have to have cold in winter in order to go dormant, and the heat indoors will cause them to come out too early in spring. Their growth will be pale and weak and unhealthy. They can be brought in for a week, now and then, and keep in a cool bright position.
Evergreens can be kept indoors safely for 2 to 3 weeks, also in a bright cool position.
Make sure not to move a tree from a warm temp to cool suddenly. Harden your tree off for a few days, leaving out during the day and in at night.
Can I keep an indoor tree outdoors?
Yes, but only in the summer from mid May to mid Sept. Most sub tropical trees cannot take frost. The Chinese elm and Ligustrum will be happy outdoors if kept in sheltered position. All trees enjoy prolonged periods outdoors in summer. It makes them healthier, happier and less prone to diseases, just like us.
Pests and Diseases.
Bonsai can be prone to pests and diseases the same as any plant. These should be treated as soon as possible as they can cause serious damage to your tree. Spray with appropriate insecticide at first sign of attack. Always spray at least twice. Red spider mite flourishes in dry, warm conditions. Spraying with water helps keep it at bay.
White fungus or mildew on leaves or soil can be caused by over watering, or lack of light. Make sure that the tree get as much light and sun as possible in the winter and kept as close to the window as possible, without it being in a draught. Also, always feel the surface of the soil before watering and do not water if wet.
Remove leaves that are badly damaged from mildew or black spot, and spray with a systemic fungicide.