Fertilizing
Feed every 2 weeks from spring to late summer with a balanced fertilizer, or once a month with solid organic fertilizer. The tree grows vigorously and uses a lot of nutrients; in early spring, a lower-nitrogen feed keeps new shoots from becoming too long.
- Reduce feeding as growth slows in late summer and stop in autumn.
- Do not feed during winter dormancy.
Placement
Place the tree outdoors in full sun all year; it loves heat and grows weakly in shade. In very hot summers, give small pots a little afternoon shade to stop the roots from overheating.
The tree is very hardy in the ground, but roots in a shallow pot are not. Protect the pot once frosts drop below about -10°C (14°F), in a sheltered spot, a cold frame or an unheated shed; it needs no light while leafless.
- It leafs out late in spring and often holds its rust-brown needles well into winter, which is normal.
Pruning
During the growing season, pinch or trim new shoots regularly to keep the shape, leaving a few leaves on each. Do structural pruning in late winter, before the buds open; the tree responds with plenty of new buds, even on the trunk.
The horizontal branches suit formal and informal upright, flat-topped and literati styles. Prune the apex of flat-topped trees harder to keep the crown low and broad.
- Wire from late spring to summer once the shoots have firmed up, or in winter when leafless.
- Check the wire often, because the shoots thicken quickly.
Repotting
Repot young trees every 1–2 years and older trees every 2–3 years, in spring as the buds begin to swell. The root system is vigorous and tolerates firm root pruning.
- Use a mix that drains well but holds water, such as akadama and pumice with some organic matter.
- Avoid plain potting compost, which compacts and becomes airless.
Watering
The bald cypress is thirsty and the soil should never dry out. In summer, water at least daily, and you can stand the pot in a shallow tray of water during hot weather.
- Do not leave it standing in water in winter or during cool, wet periods.
- In winter, keep the soil slightly moist but water much less.
Seasonal care
- Spring: Repot as the buds swell, every 1–3 years depending on age. Start feeding once the new needles appear, which can be later than on other trees.
- Summer: Keep the tree in full sun and water at least daily; a shallow tray of water helps in hot spells. Pinch new shoots and wire once they have firmed up.
- Autumn: Enjoy the rust-brown autumn color and stop feeding. The needles and small side shoots drop together, sometimes only in early winter.
- Winter: Keep the tree dormant outdoors and protect the pot from frosts below about -10°C (14°F). Keep the soil slightly moist and do structural pruning at the end of winter.
Common problems
Most problems with bald cypress bonsai come from drought, too little sun or a few pests.
- Brown, dropping needles in summer: Almost always a dried-out root ball. Water at least daily in heat and use a water tray during hot spells.
- Weak, sparse growth: Usually caused by too much shade or too little fertilizer. Move the tree into full sun and feed regularly during the growing season.
- Spider mites: Pale, speckled needles and fine webbing in hot, dry weather. Spray the foliage with water regularly and use a miticide if needed.
- Branch dieback: Fungal twig blight can kill shoot tips in damp weather. Cut out affected shoots into healthy wood and improve air circulation.