Indoor Bonsai Part I

by Marius Greeff


I can still vividly remember the Bonsai 'sermons' given at the Bonsai Garden in Tokai by 'lay-preacher' Bob Richards to all future bonsai owners and enthusiasts on how NOT to keep your tree inside the house for too long or else. A glimpse at his 'Intensive Care' unit proved exactly what he was talking about!

For some or other reason when we start off with Bonsai, we go through a stage when we believe our trees should be kept indoors and be treated the same way as a pot plant. 'Didn't 'Rev.' Richards say: 'And thou shall give it T.L.C. Yes, lots of it .• Ye hear me •. Love and Tender Care!! 'Perhaps it is a matter of pity. One believes that because the tree is so small it will not survive outside. The ultimate cure for this (I don't think Bob ever thought of that) is to give people a 'Rudi sized' tree - let them break their backs the first time and they will never again get the urge to take a tree that should be outside, indoors. Carrying a two-man bonsai in and out will kill the owner before he can kill the tree!!!

Since the popularity of bonsai is constantly on the increase, enthusiasts in North America and in Europe who have to cope with drawbacks such as harsh and extreme weather conditions or in the case of flat dwellers, the lack of outdoor areas, have to look to alternative trees for bonsai. The availability through importing of tropical species and other warm climate trees that could be kept indoors all year round and trained as bonsai, immediately facilitated this need and made the enjoyment of bonsai a far greater reality to far more people.

The whole concept of indoor bonsai received a further boost when growers discovered and realised that the trees normally used in Japan could not survive in some of the very warm and dry climates. Native species were then tried and today some of these more heat-orientated trees have become the indoor bonsai of enthusiasts from all over the world.

To us here in South Africa with our vast quantity of tropical and sub-tropical species the whole concept of indoor bonsai holds a challenge which is within everybody's reach. Success will depend mainly on our ability to match the growing needs of a given tree with the interior environment or for that matter as is done in many cases, changing the existing interior environment to suit the trees. For example where natural light is inadequate, a fluorescent light may be installed and where low humidity is a problem, it can be increased by placing the trees on a tray filled with a layer of pebbled and water.

The main problem and requirement, as with any growing plant, will certainly be LIGHT. A warm sunny south window should be suitable to most indoor bonsai including flowering species. East and west windows should be suitable for nearly all foliage plants whereas cooler windowsills that do not receive direct sun should be good for species from colder climates.


Locating the right area for your tree is very important but could at the same time prove to be very difficult to establish because it is not always easy to gauge the level of intensity of light with the human eye alone. For this special scientific light meters are available but this might be taking things too far. However any photographic light meter used by amateur photographers and set around 100ASA, will give you a reading of the relative light intensity of various locations in your home or flat. Even the light meter of your camera may be used for this and should give you a reliable indication of the areas with the highest light intensity.

When uncertain place a tree wherever you think it is suitable, then watch it very closely. A tree that has been in the same location for a few months will indicate by the colour of its foliage and shoots whether or not it is receiving adequate light. A light deficiency will be shown by long internodes (cells which stretch out to light) a poor condition by thin spindly shoots and a very definite light deficiency for proper photosynthesis by the yellowing of leaves. It is important not to fertilise any tree in this condition because it will be unable to assimilate any food and the fertiliser will burn the roots when it remains in the soil. Rather move the tree to a location with more light or replace it with a specie that can tolerate the available light.

One-sided light sources may cause lopsided growth on your tree. In this case rotate the tree regularly so that all sides receive equal light over a period of time.

Should your flat or room be too dark, you might have to consider an artificial light. The best is to go to one of the bigger electrical dealers and ask for one of the following:

  • Philips E86 (160watt) bulb
  • Cool White or Warm White Fluorescent light
  • Gro Lux Plant light

Under these artificial lighting conditions trees will require about 12 to 18 hours of light. Flowering trees will need a full 18 hours. Foliage plants will require less. Do not keep the light on all the time. Any tree or plant needs a period of darkness. For this one might have to invest in a time switch which will make things a lot easier especially when away on holiday.


A daytime temperature range of between 16 and 24 C will suit most indoor bonsai. At night it should fall to about 10 or 15 C or less. During the day the heat of the sun through a glass window may raise the temperature for a brief period to 28 - 30 C. This should not be injurious to your tree. Because temperature and light are closely related in the metabolism of a tree take note of the following: High temperatures always stimulate growth and will increase your tree's need for light. At lower temperatures (13-16 C) growth will be minimal and very high intensities of light superfluous.


Hydrometers are readily obtainable at most nurseries and will give you an indication of the exact level of humidity in the vicinity of your trees. To maintain a sufficient high humidity level it is important that all trees should be sprayed several times a week in addition to being watered. A weekly shower and leaf wash at a basin or sink will improve the general vitality of your trees. Humidity will also be increased by grouping your trees together in large flat dishes in which pebbles have been placed. Add water but see that the level of water does not touch the bottom of the pots. The water will slowly vaporise thus improving the immediate humidity level of the trees and creating a climate closely resembling that from which the tree originates. By grouping trees they will also share and retain each other's moisture and prevent its rapid dissipation over a large area.

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Maple leaves turning

red-gold in the Autumn sun

falling..... falling..... gone

Random Bonsai Tip

Where the primary branch is thinner than the secondary one, prune back the secondary hard, keep it trimmed back and allow the primary branch to grow unhindered until it has thickened.