Bonsai Care, Made Simple

Light drives photosynthesis — the process that converts water and CO₂ into the sugars your tree lives on. Without adequate light, even perfect watering and fertilising won't save it.

Indoor reality check: A south-facing window in Denmark provides roughly 500-1,000 lux in winter — a fraction of outdoor light levels. Most indoor bonsai species evolved in subtropical Asia, where they receive filtered but consistent light year-round. A full-spectrum LED grow light (5,000-6,500K, 12-14 hours daily) bridges this gap and is one of the best investments you can make for an indoor bonsai.

Outdoor placement: Morning sun with afternoon shade is ideal for most species. Direct midday summer sun through glass can scorch leaves — a sheer curtain provides simple protection. Wind exposure increases transpiration (water loss), so sheltered spots reduce watering frequency and stress.

Dormancy requirement: Temperate species (maples, pines, junipers, larch) require a cold period below 5-10°C for 6-8 weeks to enter proper dormancy. Skipping this disrupts their hormonal cycle and they exhaust themselves. These trees belong outside, with pot protection from hard frost below -5°C (wrap the pot, place in an unheated shed or garage).

Pruning serves two purposes: maintenance (keeping shape) and structural (building the design). They happen at different times and with different intensity.

Maintenance pruning: Throughout the growing season, trim new shoots back to maintain silhouette. The guideline "let it grow 3-4 nodes, cut back to 1-2" works for most deciduous and broadleaf evergreen species. This promotes ramification — the development of fine, dense branching that gives bonsai its mature look. More ramification means more leaves, which means smaller individual leaves — the miniature effect compounds over years.

Structural pruning: Best done in late winter or early spring before growth begins, or in late autumn after leaf drop for deciduous trees. This is when you remove entire branches, correct flaws in the design, or make major directional changes. A concave cutter leaves a wound that heals flush with the trunk — flat cuts create visible scars. Seal large wounds (over 5mm) with cut paste to prevent dieback and infection.

Wiring: Copper or aluminium wire wrapped around branches lets you bend them into position. Apply at roughly 45° angle, not too tight (leave room for the branch to thicken). Check every few weeks — wire left too long cuts into the bark and leaves permanent scars. Remove by cutting the wire off in sections rather than unwinding, which can snap branches.

Defoliation: For deciduous species only, removing all leaves in early summer triggers a second flush of smaller leaves. This is an advanced technique — never defoliate a weak or recently repotted tree.

Plants need three primary macronutrients: nitrogen (N) for leaf and stem growth, phosphorus (P) for root development and flowering, and potassium (K) for overall health and disease resistance. Bonsai fertilisers are labelled with NPK ratios — a balanced 7-7-7 or 6-6-6 works well for general use.

Feeding strategy through the season: In spring, use a slightly higher nitrogen ratio to support the initial growth flush. Through summer, maintain balanced feeding. In early autumn, switch to lower nitrogen and higher phosphorus/potassium to harden off growth before winter. Stop feeding dormant trees entirely.

Organic vs. chemical: Organic fertilisers (fish emulsion, seaweed, bone meal) release slowly and improve soil biology. Chemical fertilisers are immediately available and precisely dosed. Many growers use both — solid organic pellets for steady baseline nutrition, liquid chemical feed for precise supplementation. Neither is "better" — they serve different purposes.

Soil composition: Bonsai soil is not potting soil. It's a granular, fast-draining mix. The standard blend is akadama (water retention), pumice (aeration), and lava rock (drainage), typically in equal parts. Akadama is a Japanese volcanic clay that holds water while allowing oxygen flow. It breaks down over 2-3 years, which is one reason repotting is necessary. For species that prefer more moisture (like Chinese elm), increase the akadama ratio slightly. For arid species (pines, junipers), increase drainage components.

A tree needs repotting when you see these signs: water pools on the surface instead of draining through, roots circle the bottom of the pot or push out the drainage holes, or growth has slowed noticeably despite good care. To confirm, gently lift the tree from its pot and inspect the root ball.

Root pruning technique: Using a root hook or chopstick, gently comb out the roots from the bottom and sides, removing old soil. Trim back roughly one-third of the root mass, focusing on thick, downward-growing roots and any that are circling. Keep the fine feeder roots — these are what actually absorb water and nutrients. The goal is a shallow, spreading root system (nebari) that anchors the tree visually and physically.

Repotting steps: 1) Cover drainage holes with mesh to prevent soil loss. 2) Add a layer of fresh soil. 3) Position the tree — slightly off-centre is often more natural-looking than dead centre. 4) Work soil into the roots with a chopstick to eliminate air pockets. 5) Water thoroughly until the runoff runs clear.

Aftercare: Keep the repotted tree in a sheltered spot out of direct sun and strong wind for 2-3 weeks. Don't fertilise for the first month — the fresh soil has enough nutrients and the cut roots need time to heal before absorbing fertiliser salts.

Systematic diagnosis beats guessing. Work through these categories in order:

1. Water stress: Overwatering causes root rot — leaves yellow, wilt despite wet soil, and the tree declines from the bottom up. Smell the soil; a sour odour confirms rot. Stop watering, improve air circulation, and in severe cases, repot into fresh dry soil and trim any black/mushy roots. Underwatering causes dry, crispy leaf edges, drooping, and rapid leaf drop. The soil pulls away from the pot sides. Submerge the entire pot in water for 10 minutes to rehydrate, then resume normal watering.

2. Light deficiency: Long internodes (spaces between leaves), larger-than-normal leaves, pale colour, and leaning toward the light source. The fix is more light — introduce gradually to avoid sunburn.

3. Pests: Spider mites cause fine webbing and stippled, pale leaves — they thrive in dry indoor air. Scale appears as small brown bumps on branches and leaf undersides. Aphids cluster on new growth. For all three: isolate the tree, spray with insecticidal soap or neem oil, and repeat every 5-7 days for 2-3 cycles to catch hatching eggs. Increasing humidity deters mites.

4. Nutrient issues: Uniform yellowing of older leaves suggests nitrogen deficiency. Yellowing between veins (interveinal chlorosis) suggests iron or magnesium deficiency. Both are solved by resuming balanced fertilisation — but check pH first, as incorrect pH can lock nutrients in the soil even when they're present.

5. Temperature shock: Sudden leaf drop after a cold night near a window or a draft from a door. Most indoor species recover if returned to stable conditions. Frost damage on outdoor trees shows as blackened, wilted shoot tips — prune these back to live tissue in spring.