Indoor Bonsai

I must start by saying that there are no such thing as "Indoor" bonsai!, however any plant originating from Tropical or Sub-tropical, but kept in Temperate areas of the world will need to be kept in a warm, well lit environment when the weather outside may harm them. Under no circumstances should any tree from an area of the world subject to 'Hard' winters be kept in a heated and lit environment over winter in the mistaken belief that they are far more delicate than they in fact are. Doing this is a sure way to kill your tree. Indeed no tree from a 'temperate' part of the globe should be kept indoors for more than a few days viewing.

If the species you wish to keep originated in the tropics and if you live outside of the tropics, the tree will need protection, but may be kept outdoors in the summer.

If you live in the tropics and the tree originated there, the only constraint on keeping the tree indoors would be the amount of light available, matched to the needs of the plant, for example, if you are growing a tree that survives in dense rainforest, it will have evolved to cope with low light situations.

Feeding

Indoor bonsai continue to grow throuout the year and should be fed all year.

Light

When the climate is suitable put your (indoor) trees outdoors they will benefit from the extra light. As indoor bonsai tend to be kept by flat dwellers this may be either on a balcony or on a windowsill (secure them down to avoid them landing on someone's head).

Providing adequate light for you indoor trees is going to be your biggest problem, unless you are going to provide artificial lighting your trees will need to be placed as close to a window as possible. Plant growth in low light situations becomes long and pale.

The illustration below shows the 'Inverse square law', a law known to photographers.

Light radiates outward from a source (in this case the Sun), so light passing through a window is radiating outward, theoretically every time you double the distance of the tree from the window the amount of light falling on the tree is quartered. This may seem difficult to believe, but over the millenia the human eye has evolved to compensate for differences in light levels, so we could see the bear asleep at the back of the cave we were about to move into. Plants do not have this advantage, so in practice, keep your trees as near to the window as possible and see what I say below about rotating them.

A normal and an etiolated shoot under sun and artificial lighting.

A lack of light will cause growth to become thin and pale. This is called 'etiolated growth' and such growth has a greatly reduced potential for photosynthesis and limit the plants ability to produce food.

Bonsai kept indoors, in inadequately, or improperly lit places, will be prone to this.

Heat

It is not a good idea to subject any plant kept indoors to sudden temperature changes, nor should they be placed near a heat source. Do not place your trees on an inner windowsill, with the trees trapped between the drawn curtains and the window, the temperature at night can be a lot lower in this area.

Humidity

One of the problems with keeping any plant indoors, is that whatever source of heating you provide, it will unless you are careful, dry any moisture out of the atmosphere in the room. This can be overcome, by standing your trees on trays full of gravel, or one of the clay pellets such as Hortag. The gravel, or pellet being immersed in water. Evaporation of the water will provide a moist microclimate, around the tree.

There is I should point out a down side to this, that being the possible damage to the house/contents, caused by condensation.

Rotate your trees

The main function of leaves is to turn light into food for the tree. The tree will not put energy into producing or maintaining branches and leaves where they will get no light, they will in fact shed those branches. To maintain a tree with 'depth' you will need to rotate you trees so that both the front and back get an adequate amount of light.

This may mean turning the tree around for a week or so every month, but it's better to look at the back of a tree with a full set of branches, than something with all the visual 'depth', of a cardboard cut-out.

The Illustration to the left shows the sun's passage around a tree, with little light getting to the branches at the back. This, in a tree kept indoors will usually be on the room side of the tree, foliage and branches there will die if not given enough light.

Artificial Light

Artificial lighting is a great way of keeping your indoor trees healthy, if used in conjunction with natural light.

Daylight may be considered to be made up of the three primary colours Red, Green and Blue, although blue is by far the largest component and the best suited to photosynthesis. Green light is for the most part reflected off the leaf and its this reflected light that gives leaves their colour.

Avoid using normal household filament and fluorescent lamps as they do not emit light at the right wavelengths for healthy plant growth, go for lamps from specialist suppliers, usually they advertise in gardening or aquatic magazines.

Tungsten filament lamps emit a continuous spectrum peaking in the red area and falling away in the blue, the colour most suited to Photosynthesis, reducing the plants ability to turn light into energy.

Flurescent lamps emit a different spectrum, with peaks at varying wavelengths depending on the type of lamp. Some tubes, particularly those made for the Aquarist trade will give a good approximation of daylight.
The impact of unsuitable lighting on trees kept indoors cannot be understated. If you must keep bonsai indoors please talk to your local garden center about appropriate lighting.

Displaying your trees

Indoor trees can be shown on a stand like that to the right, however care must be taken to protect the stand from water.

Allen. C. Roffey 09:50 13/07/2008