Bonsai care: watering, feeding, pruning and repotting

A bonsai is an ordinary tree in a very small pot. That is the whole challenge: little soil means little buffer. Water, nutrients and root space run out much faster than in the ground. Good care mostly means checking your tree regularly.

Indoors or outdoors?

It depends on the species, and it is the most important question of all.

• Outdoors: Most bonsai are temperate trees such as Japanese maple, pine or juniper. They need sun, wind and the change of seasons, winter included. Most bonsai cannot survive indoors long-term because indoor light is much weaker.
• Indoors: Tropical and subtropical species such as ficus. Chinese elm and olive are also often kept inside. They need bright light, steady temperatures and humidity.

Each species profile tells you where your tree belongs.

Watering: the most important task

There is no fixed watering schedule. How much water a bonsai needs depends on weather, season, pot and soil.

1. Check: push a finger about 1 cm into the soil. If it feels slightly dry there, water.
2. Water thoroughly: until water runs out of the drainage holes. Wait a moment and repeat so the whole root ball gets wet.
3. Water gently: use a fine rose so the soil is not washed away.

In summer this can mean once or twice a day. Rainwater works best. Keep checking in winter too: one dry week can catch you out.

The more common mistake is the opposite: soil that stays wet all the time makes the roots rot. More in How to water a bonsai.

Feeding: little but often

Nutrients in a small pot are used up quickly. During the growing season, give a balanced liquid feed at a low dose about every two weeks.

A proven feeding rhythm:

Period	How often
Spring to mid-July	every 1–2 weeks
Mid-July to October	every 2–3 weeks
From November	stop

More is not better: too much fertiliser produces soft growth that attracts pests.

Pruning: keeping the shape

Pruning keeps the tree small and compact. The right time depends on the species:

• Deciduous trees: late winter to early spring.
• Conifers: autumn or winter.
• Japanese maple: autumn to early winter, because it "bleeds" heavily in spring.
• Pines: shorten the new shoots (candles) by a half to two thirds in spring.

During the season new shoots are also pinched back with fingers or scissors. On maples, one or two pairs of leaves are left.

Repotting: fresh soil, trimmed roots

Over time the roots fill the pot and the soil compacts. That is when you repot.

• When: in spring, just before the tree starts to grow.
• How often: most trees every 2–3 years. Pines only every 3–5 years, fast growers every year.
• Roots: about 2–3 cm of the outer roots are often trimmed.
• Soil: one example mix is 2 parts compost, 2 parts grit and 1 part loam-based compost.

After repotting, keep the tree in a sheltered, partly shaded spot for a few weeks until it has re-established.

Overwintering

Outdoor trees need winter to rest. Too much protection weakens them. In a small pot, though, roots freeze much faster than in the ground. That is why bonsai collections are often stored just above freezing in winter (33–36 °F / 1–2 °C).

When something is wrong

The most common problems are vine weevil, scale insects, slugs and snails, and powdery mildew. Yellow leaves, mould on the soil or fine webbing? The Bonsai Doctor helps you find the cause.