How to grow and care for an indoor bonsai tree

Bonsai tree care

Caring for an indoor bonsai tree is slightly more challenging than caring for house plants because bonsai trees are planted in small pots so the roots have less compost from which to take water and nutrients. This means you need to water, feed and repot them more often than standard house plants. What's more, most indoor bonsai trees are native to tropical or subtropical regions and therefore need conditions with plenty of warmth, light and humidity. However, given the right conditions and level of care there's no reason why bonsai trees won't thrive alongside regular house plants indoors.

In this short video guide, the experts at Cheshire Bonsai Society, share their top tips for growing bonsai, including how to water them and which trees to keep indoors and which to grow outdoors.

Where to site an indoor bonsai tree

Indoor bonsai trees are from tropical and subtropical regions and therefore need plenty of warmth, light and humidity, so position your tree in a well-lit spot but out of direct sunlight, in a naturally humid room such as a kitchen or a bathroom. If the room isn't humid enough then place your bonsai tree on a wide humidity tray or saucer filled with pebbles and a little water – the water needs to sit just below the top of the pebbles so it's not absorbed by the bonsai tree roots. Alternatively, mist your bonsai tree daily to keep humidity levels up.

The temperature of the room should remain fairly constant throughout the year: tropical species do best in rooms with an average temperature of around 20ºC with lows of no less than 15ºC, while those from subtropical habitats can withstand slightly lower winter temperatures, down to a minimum of around 7ºC.

How to grow your own bonsai tree from seed

Growing bonsai trees from seed is known as Misho in Japanese. Starting from scratch gives you complete control of the shape and form of your bonsai tree but requires a lot of patience – the tree should be around three years old before you can start to shape it.

You may have been gifted a bonsai kit or sourced your own seed. If sourcing your own tree seeds make sure you buy seeds of tropical or subtropical species, which thrive in an indoor environment.

Bonsai kits come with compost and a pot but if you have sourced your own seed you will need to buy compost – bonsai trees should be grown in special bonsai substrate as multi-purpose compost can be too water retentive and can lead to root rot, but loam-based or multi-purpose compost is fine for sowing seeds. You will also need a pot. Initially it's best to sow seed into a small pot designed for seedlings but eventually you will need to buy a bespoke bonsai pot, which you will find from a bonsai specialist seller.

Depending on the seed you buy, you may need to prepare it before sowing. Many temperate trees require stratification (a period of cold) to germinate, but tropical and subtropical trees usually don't need this. However they may need scarification, which is the act of nicking the hard seed coat to let water in to aid germination. Species such as Schefflera can be tricky to germinate so are best soaked in water before sowing, however your bonsai seed kit or individually bought seed should come with notes as to whether the seed needs scarifying or not.

To scarify seed use a sharp gardening knife or pair of nail clippers to nick the outer coating of the seed, to allow water in. You can also use a nail file or sand paper to rub off the tough outer coating, or soak the seed in water for up to 24 hours.

1. Once you have scarified your tree seeds, sow them evenly over the surface of moist bonsai substrate in a small (10cm) pot. Cover with a layer of substrate (around the same depth as the size of the seed itself, but this will vary depending on the plant) and gently firm with your knuckles. Water gently so as not to dislodge the seeds you have sown, and allow to drain. Cover the pot with a clear plastic bag held in place with an elastic band and keep in a bright spot out of direct sunlight, at room temperature.
2. Your tree seeds should germinate in around six weeks. Remove the bag when the first true leaves have grown, then, after a few weeks, pot the seedlings into individual pots of fresh bonsai substrate and keep well watered

How to repot a bonsai tree

The first repotting of your bonsai tree is probably the most important, and should be done within a year of you sowing the seed. When trees grow they develop a tap root, which anchors them into the soil. With bonsai you should remove this root to allow the lateral roots to grow evenly.

1. Before you remove the tap root make sure you have everything ready so the roots aren't exposed for too long. Choose a small bonsai pot and enough bonsai substrate to fill it. Fill the pot with the substrate and make a hole in the centre for the root mass to sit comfortably
2. Then remove the tree from its original pot, identify the tap root (the long main root) and carefully remove it with scissors. It's a good idea to spray the roots with water during this process so they don't dry out
3. Carefully place the root mass into the hole so it's sitting just below the surface. When you're happy with its position firm the substrate around the root ball and water well

After the initial repotting, you should aim to repot your bonsai tree every two to five years to prevent it from becoming pot-bound. Repot young trees more regularly than old trees. Only repot your bonsai tree as it starts to become pot-bound – check it in spring by carefully removing the tree from its pot. If you see the roots circling around the root system, your tree needs to be repotted. If the roots are still contained within soil, leave it and check again the following spring.

The best time to repot a bonsai is in early spring, as even tropical species grow more slowly at this time than at other times of year.

1. Choose a pot that fits the size of your tree – it could be the same pot or a slightly larger pot, which should typically be of the same length as the trunk. Make sure you have enough fresh substrate to hand
2. Using a chopstick or similar implement, carefully remove the old substrate from the roots. Leave some in place as there may be some beneficial mychorrhizal fungi that helps provide nutrients to the roots
3. Cut away any roots that have grown too long, with sharp scissors. Don't prune more than a third of all roots
4. Cover drainage holes with mesh to prevent the substrate from falling out, and fill with fresh substrate. Make a hole to fit the root ball and position your bonsai tree in place, firming only when you are happy with its position. You may want to fix a wire to stabilise the roots into the pot. Water thoroughly

How to care for an indoor bonsai tree

Bonsai trees need a little extra care than regular house plants. They are grown in small pots so have less available nutrients and water than regular house plants. Also, as tropical and subtropical trees, indoor bonsai need steady temperatures, along with plenty of light and humidity.

Check the substrate daily to see if you need to water, and add water only when the substrate starts to lose moisture (the compost should feel damp). However it's important that you don't let it dry out between waterings. If you do find the substrate has dried out, submerge the whole pot in water for around 10 minutes and then leave to drain.

Fertilise regularly (every one to two weeks) with a specialist bonsai fertiliser to make up for the lack of nutrient availability in the soil. If you have a bonsai tree kit or you buy a bonsai tree from a specialist supplier, you will be advised on when and how to fertilise, as this depends on species and age of your tree.

In winter you may need to move your bonsai tree closer to a window so it gets more light. Take care to avoid hot radiators.

In summer you may need to move your bonsai further away from windows as it could overheat or suffer from leaf scorch.

How to prune an indoor bonsai tree

If growing your bonsai tree from seed you will need to shape it, and you can wrap wire around the stems to slowly bend them to a desirable form. Once you have set your desired shape you will need to maintain it by pruning regularly. As a general rule, identify shoots 2-3cm long and cut them back to the first pair of new leaves. Hard pruning and any reshaping should be done in early spring, before new shoots grow.

Pests and diseases

Like all indoor plants, indoor bonsai trees are susceptible to pests such as scale insect, red spider mite, greenfly and fungus gnats. By regularly inspecting your tree you can identify these pests and deal with them quickly.

Other problems could develop if you don't provide your bonsai tree with the conditions it needs. Root rot can lead to the death of the tree and is caused by overwatering and not enough drainage. Powdery mildew is a powder-like fungus that prevents the leaves from being able to photosynthesise properly, and can be caused by too dry compost. Yellowing of the leaves suggests your bonsai is deficient in nutrients while leggy, etoliated growth means your bonsai tree isn't getting enough light.

Bonsai trees best for indoors

Ficus bonsai

The easiest to care for, Ficus bonsai (Ficus retusa and Ficus benjamina) are best indoor bonsai for beginners. Ficus are tolerant of lower humidity and light levels than most other bonsai trees, so need a little less care.

• Buy Ficus microcarpa 'Ginseng' from Crocus
• Buy Ficus bonsai from Thompson & Morgan

Hawaiian umbrella (Schefflera) bonsai

This species copes well with low light and humidity, similar to the ficus, but if you want a shaping and training challenge this one isn't for you as it doesn't do well with wiring.

• Buy Schefflera from Crocus

Chinese elm bonsai

Ideal for beginners, Chinese elm grows quickly and tolerates a lot of pruning and training. Also fairly tolerant of irregular watering.

• Buy Chinese elm from Bonsai Direct

Carmona bonsai (fukien tea)

A popular bonasi tree that needs a lot of light and a constant room temperature of around 20ºC. Be careful to boost humidity in winter, as central heating tends to create a drier environment indoors.

• Buy Carmona bonsai from Bonsai Direct