Care of indoor bonsai
Indoor bonsai have become extremely popular over recent years
and have gradually developed from the original cultivation of outdoor trees
collected from the wild.
Indoor bonsai are miniature versions of mainly sub-tropical
and tropical trees and shrubs, whose native climate is hot and often very
humid. Most species can be adapted to live inside a house or heated glasshouse,
but a normal house environment though does not entirely correspond to the
natural environment of the tree growing in the wild, even though they may
initially look healthy. Central heating is the worst culprit as it can
produce a very dry atmosphere and most indoor bonsai find this too dry and not
Many tropical plants are suited to an indoor climate because
in their native countries there are scarcely any seasons and little variation
in temperature. Nevertheless, they still often require very moist and
Other plants like the Olive, Pomegranate and Myrtles grow in
the Mediterranean regions and are classed as sub-tropical. They require
some humidity, frost protection and a dormant period in winter.
All plants with small leaves and branches that are not too
woody are particularly good for training as bonsai.
- Most indoor bonsai require plenty of light, water and air
during the summer.
- Always shade the bonsai from direct scorching sunlight and
feed once every two weeks.
- Tropical indoor bonsai should be kept in a temperature of
between 18°C - 30°C during the day and 16°C - 20°C at
- Sub-tropical indoor bonsai require cooler summer
temperatures of 15°C - 26°C and winter temperatures between 8°C -
15°C. Because they undergo a dormant period unlike tropical plants
they often drop their leaves during the winter, and may look dead. They need to
be kept just moist, but should not be allowed to dry out at any time.
- Sub-tropical indoor bonsai need regular pruning every month
or so during the period March to October, especially when it is very hot and
- Tropical indoor bonsai, if kept in the house, will require
pruning every month throughout the year.
- All shoots need to be pruned back to two or three nodes or
leaves which will encourage the plant to produce twiggy growth and back budding
to produce new branches.
- Older bonsai need only be pruned back after flowering, and
to shorten back any long growths.
- Wiring of branches can be carried out at any time of the
year but only wire shoots from late summer once they have become mature and
slightly woody. Many indoor bonsai have very brittle and delicate trunks and
branches. Great care must be exercised in wiring these and may be best done in
the spring when a greater amount of sap is rising.
- Wire should not be applied to flowering shoots.
- DO NOT wire too much of the tree at any given time because
this will over stress the tree and may kill it.
- All indoor bonsai require a cool airy position all year
round with diffuse bright light facing north, east or west but if kept on a
window sill, must not be left between the curtains and window in winter.
- If light levels become too low in winter supplementary
lighting may be required.
- Most bonsai can be kept outdoors during the summer in
semi-shade from late spring till early autumn, but keep a check on watering if
it is very windy.
- During spring, summer and autumn water demand will be a
great deal more than in winter, and it is often beneficial to site the bonsai
on a tray of pebbles or pea gravel in a dish beneath to help maintain
- During the summer especially the compost can be allowed to
dry out a little before watering, but it should never be allowed to dry out
- If bonsai become very dry the plant must be totally
immersed in a tub or bowl of water until the air bubbles stop emanating from
the compost, usually for up to 15 minutes at least. Remove and allow to
- If possible always use soft water (usually rainwater).
- Always use water at room temperature and never water the
bonsai out in the full sunshine as this may well produce leaf scorch.
- It is important to maintain nutrients to indoor bonsai and
feeding should be carried out during spring to autumn using a liquid feed when
watering every two weeks.
- It is always better to use too little than too much
fertilizer particularly when using inorganic feeds. DO NOT over feed with
inorganic fertilizer as this may cause root damage.
- Using organic fertilizers such as pelleted chicken manure
is very beneficial to the tree as no scorching of the foliage and roots can
- Ensure the bonsai is well watered beforehand.
- Young and fast-growing trees need more feeding than old and
slow-growing species in order to thicken the trunk and build new branches
- DO NOT use the same fertilizer all through the growing
season - try to alternate, and use a phosphrogen based fertilizer in the
- DO NOT feed bonsai shortly before and during flowering,
after re potting, after root pruning, during the dormant period and if the tree
is in an unhealthy condition.
Potting and repotting
- Most indoor bonsai require a loam-based compost made up of
a combination of loam, sieved peat free compost and sand or grit. The
mixture below is generally adequate for most species:
Two parts loam,
(John Innes potting No 2 or 4 is adequate)
Two parts peat free
compost or leaf mould
One part sand or grit
- Acid loving species like Gardenia, Azaleas and
Rhododendrons need an ericaceous compost which has a much higher ratio of peat
One part acidic loam or pure Kanuma compost
Four parts moss
or sedge peat, (ericaceous compost).
Two parts sand or grit
fertilizer granules (optional)
- Generally these mixtures should be adequate for about two
to three years but calcium- or rain-free water must be applied as much as
possible when watering
- Repotting of established indoor species should be carried
out every two to three years and very young vigorous plants, every year.
If the roots are pot-bound they should be teased out carefully before
trimming. Trim off at least one-third to one-half of the roots only.
- The same bonsai pots can be used for very old and mature
indoor bonsai but a larger one may be required for young and fast-growing
plants, which require further growth and training.
- When choosing a new pot ensure that it has drainage holes
in the base and that the tree looks to scale in the pot. Also position
the tree correctly in the pot.
Pests and diseases
- A number of pests and diseases attack indoor bonsai and it
is important that every plant is examined closely every week to ensure that no
pest or disease is becoming established.
- If the plants are well looked after and healthy they will
be much more able to resist attack by most pests and diseases.
- Indoor bonsai can often be more severely attacked than
outdoor bonsai because they are kept in a much more protected environment.
- Always use a biological control where possible instead of
chemical treatments which may also kill many beneficial insects. This is
as effective and safer, but often takes a little longer to work than
- The most commonly found pests are:
|Vine weevil (adults and
||Biological control Nemasys-H
or 'Provado' for larvae
|Leatherjackets (larvae of
||Use soil drench of
|Aphids (Greenfly and
||Apply a soap solution or
||Scrape off with a knife and
||Spray with 'Provado' or
||Use 'Provado' or Methylated
||Use a 'Provado'soil
|Red spider mite
||Spray with insecticide or use
||Biological control (Encarsia
- For small infestations water spray or a solution of soapy
water often controls aphids and red spider mite.
- Diseases are just as damaging as pests and need to be
identified early on so control measure can be taken. The most common
||Remove all dead roots and pot
plant into new soil and do not water for at least 2 days. Water with
||Spray with Nimrod T or other
||Spray with Nimrod T, Copper
fungicide or systemic
||Spray with Nimrod T, Copper
fungicide or systemic
||Evident on acid-loving plants
where a lack of iron causes yellowing of the leaves. Treat with chelated iron.
|Damping off of seedlings
||Soil drench compost with
Chestnut compound, Dithane, Sythane, Copper fungicide or 'Filex'.
© 2011 Colin Carpenter (revised June
The site provides information on the history of bonsai,
different species and how to propagate them, and details of workshops on the
art of bonsai growing and the care of bonsai, trees for sale, and of a
©2010 Colin Carpenter