Indoor Bonsai – Advice and Care
If you ask the average person on the street what a Bonsai is, they automatically conjure up an image of a little tree sitting on top of the television or coffee table. A lot of people think that Bonsai can only be kept indoors. This is not true as the majority of Bonsai are for outdoor cultivation, but in recent years there has been an increase in the number of tropical and sub-tropical Bonsai being sold. This is due to the demand for trees that can grow indoors. This handout will explain what an indoor tree is, the most common varieties available, and how to care for them.
An indoor Bonsai is quite simply a tree or shrub whose normal habitat is similar to that of your home. E.g. A tree that likes an even temperature of between 10 – 20 c all year round. The majority of our native trees and shrubs will not tolerate these conditions for more than a few days at a time before showing signs of ill health. So the solution is to go to a tropical or sub-tropical region and use whatever trees thrive there, as indoor bonsai over here.
CARING FOR INDOOR BONSAI
First thing’s first. You need to make sure that you have somewhere in your home where you can display your tree and also ensure that it will thrive. There are two main factors that allow you to grow bonsai indoors, light and temperature.
If the tree is placed in a dark corner it will become tall and leggy with long spaces between sets of leaves. Photosynthesis, which produces the vital sugars and starches in the leaves, is slowed down and growing tips can turn black. Therefore, the tree must be placed where it will receive good natural light but no direct sunlight, which may burn the leaves.
The majority of Indoor Bonsai like a balanced temperature between 10 – 20 c. During the summer, a slightly higher average of between 16 – 22 c is ideal but not absolutely necessary. In winter, temperatures should not fall below 10 c although some sub-tropical trees will tolerate lower temperatures. These temperatures are only a rough guide as each species of tree has its own specifications that will be explored in more detail at a later stage.
Never place a Bonsai over a source of heat such as a radiator or an electrical appliance. You would not believe how many bonsai die because they are kept on top of the TV You can forget that it can be twice as hot as the room temperature but your bonsai can’t. The soil heats up and the roots fry. Another favorite place for Indoor Bonsai is on the window sill. This is fine during the day as long as it does not get too much direct sun, but when you close your curtains at night, the air temperature around your Bonsai can drop quite dramatically if it’s cold outside. Again this will depend on the species of tree but, to be on the safe side, bring the tree into the room at night. So, avoid placing your Bonsai in a drafty area, although they like good air circulation, the sharp changes in temperature caused by a draft will harm some tropical trees.
After reading the last paragraph, you may think that it is very hard to place your tree, but it is mostly a case of common sense. Most people have a coffee table or shelf in a bright room which will be ideal.
Now that you have found somewhere to place your tree we will discuss how to care for it. This includes watering, feeding, pests and diseases and repotting.
This is the most important part in caring for an Indoor Bonsai. Never let the soil dry out. It is probably wise to water your tree every day, and once a week submerge the pot and soil in water until the air bubbles stop coming to the surface. Do not make the common mistake of treating it like a house plant. This is a tropical tree that, if at home, would probably be in a rain forest getting well watered every day. It is also a good idea to mist the tree as often as possible. This is not always practical when you are at work all day, but you can substitute misting with a humidity tray of damp grit or pebbles below your tree. All trees will love you for it and will grow more vigorously due to a higher level of humidity duplicating their natural habitat.
Between March and October you should feed your indoor trees every two weeks with a fertilizer containing N.P.K. of around 7:7:7. Although indoor trees grow all year round it is a good idea to give them a break over the winter months. Do this by only feeding once a month over this period and feed with a fertilizer containing very little Nitrogen eg. tomato feed or 0:10:10. During the growing season you can also feed using fertilizer pellets that are slow release and therefore require fewer applications. Do not over feed your tree and never feed a tree showing any signs of ill health.
PESTS AND DISEASES
Indoor trees do not suffer from pests as much as their friends outdoors due to their inaccessible location which deters a lot of insects which fly or crawl. This does not mean they are immune so check periodically and spray at the first sign of trouble. Watch out for red spider mite and whitefly. Bad air circulation may cause some species to develop mildew. Treat as first signs appear.
An indoor tree can be repotted at any time of the year, but for best results repot in Spring. For details on how to repot a tree please refer to previous handouts as all Bonsai are repotted in the same manner. A good tip is not to use peat if there isn’t any in the soil you are replacing. A tree which has grown all its life in a peat free soil can sometimes find it a bit of a shock coming in contact with a substance totally alien to its natural environment. Another tip is to remove the Chinese clay that the majority of imported trees arrive in and replace it with Akadama (Japanese clay) or Biosorb(British equivalent of Akadama). These two substances allow the water easy access into the soil, and will stay moist longer than the original Chinese clay. Akadama also has the added bonus of turning a lighter colour as it dries which is an excellent indicator of when to water.
Throughout this handout, I have mentioned how each species favours different conditions. I.e. Tropical trees needing more heat and water than a sub-tropical. So to help you find the right tree for your home, I will list a few which are the most commonly seen for sale in Northern Ireland. I will give them a difficulty to grow star rating from one for hard up to five for easy. This will only be my view but if you want to check before buying read a good book on Indoor Bonsai. There are plenty on the market.
Buxus Harlandii (Box) *****
Sub-tropical - China
Adaptable to changing temperatures, can go outside in summer. Slow growing. Allow to dry out slightly before watering.
Carmona Microphylla (Fukien Tea) *
Tropical - Asia
Very sensitive to temperature, minimum 15 c. Bears white flowers. Constant humidity needed. Some people are allergic to its leaf. Only for the brave at heart.
Ficus (Fig) ****
Tropical - Asia, Australia
Avoid sudden temperature changes. Tolerates low light levels. Types – Benjamina, Carica, Retusa.
Murraya Paniculata (Jasmine Orange) ***
tropical - asia
Mist frequently. Temperature should not drop below 12 c or it will drop leaves which will regrow once placed in more suitable spot.
Nadina Domestica (Sacred Bamboo) ****
Sub-tropical - Japan
Keep moist. Tolerates colder temperatures. Needs good sunlight to maintain colour. Ideal for a colder room.
Podocarpus Macrophyllus (Podocarps) ****
Sub-tropical - Japan, China
Robust tree. Likes sunlight in summer and foliage misted regularly. When well cared for will bear fruit.
Portulacaria Afra. (Jade) **
Succulent - South Africa
Some people would debate its suitability for Bonsai but it can be pruned to a tree like shape. Likes direct sunlight. Water sparingly during summer.
Punica Granatum (Pomegranate) *****
Sub-tropical - Asia, Mediterranean
Keep soil moist. Avoid too much sun in summer. Bears orange flowers readily. Grow your own from seed.
Sageretia Theezans (Theezan Tea) ****
Tropical - Asia
One of the sturdiest tropical trees. Water generously, mist regularly. Watch out for mildew.
Serissa Foetida (Tree of a thousand stars) *****
Tropical - Asia
Vigorous grower. Avoid too much sunlight and sudden changes in temperature. Bears white flowers.
Ulmus Parvifolia (Chinese Elm) ******
Sub-tropical - China, Korea, Japan.
The best tree in my view for Indoor Bonsai. Vigorous grower and very forgiving when under watered. Water when soil begins to dry. Can be kept outdoors but becomes deciduous and needs frost protection. Ideal for first indoor tree. (Six stars is not a mistake!)
Acacia Dealbata (Silver Wattle) ***
Bougainvillea Glabra (Paper Flower) ***
Citrus (Oranges etc.) ***
Fuchsia (dwarf flowering) ***
Ligustrum Sinense (Chinese Privet) ****
Olea Europaea (Olive) **
Pistacia Terebinthus (Pistachio) ****