Fertilizing
Willows grow fast and are hungry trees. Feed every two weeks from the moment the leaves have opened in spring until late summer, using a balanced organic or mineral bonsai fertilizer.
- Do not feed for four to six weeks after repotting, or while the tree is weak or stressed.
- A low-nitrogen feed in early autumn helps the shoots ripen before winter; stop once the leaves turn yellow.
- Do not feed during winter dormancy, and follow the dose on the label to avoid root burn.
Placement
Keep your weeping willow bonsai outdoors all year in full sun, with at least six hours of direct sun a day. In regions with hot summers, light afternoon shade prevents leaf scorch and reduces how often you need to water.
Turn the tree regularly for even growth and keep it out of drying winds. It is very hardy, but protect the roots in the pot when temperatures fall below -10°C (14°F), for example by sinking the pot into the ground or placing it in an unheated shed.
Pruning
Willows grow extremely fast, and the long hanging shoots are renewed every year. In early spring, before the buds break, cut the previous year's shoots back hard to one or two buds; the new shoots that follow will form the weeping curtain.
- During the growing season, pinch shoots growing upwards and shorten hanging shoots that become too long.
- Thin the canopy regularly so light reaches inner and lower branches, which otherwise die back.
- Large cuts heal poorly and can rot, so avoid them where possible and seal any you make.
- To guide young shoots downward, wire them carefully in late spring or early summer, or weigh them down.
Repotting
Willows produce roots very quickly. Repot young trees every year and older trees every two years, in early spring as the buds start to swell; willows leaf out early, so do not wait too long.
- You can remove up to about half of the root mass on a vigorous, healthy tree.
- Use a bonsai mix that drains well but holds plenty of water, for example akadama with some pumice.
- Choose a pot deep and wide enough for the root system and stable enough for the hanging growth.
- Afterwards, keep the tree sheltered from strong sun and wind and evenly moist while it re-establishes.
Watering
Weeping willows are water-loving trees: never let the soil dry out. Check the tree at least once a day and water thoroughly as soon as the surface feels slightly dry.
In hot summer weather you may need to water several times a day, and a humidity tray helps during heat waves. Good drainage is still essential, so never leave the pot standing in water. In winter the tree is dormant: keep the soil slightly moist.
Seasonal care
- Spring: Willows leaf out early, so repot in early spring as buds swell and cut the long hanging shoots of the previous year back hard. Start feeding once the leaves have opened, but not in the first weeks after repotting.
- Summer: Water abundantly, often several times a day in heat, and give some afternoon shade to prevent leaf scorch. Keep feeding every two weeks and pinch new shoots regularly.
- Autumn: Switch to a low-nitrogen feed in early autumn and stop once the leaves turn yellow. After leaf fall, dead and crossing branches are easy to see and remove.
- Winter: The tree is dormant and needs the cold, so keep it outside but protect the roots below -10°C, for example by sinking the pot into the ground. Keep the soil slightly moist; do not feed.
Common problems
Weeping willows are vigorous but thirsty, and they are prone to a few typical pests and diseases.
- Leaf scorch and sudden leaf drop: The root ball dried out or the tree stood in intense afternoon sun. Water more often in summer, add afternoon shade and consider a humidity tray in heat waves.
- Aphids and caterpillars: Aphids cluster on soft shoot tips, and willow sawfly or moth larvae can strip leaves quickly. Check the tree regularly, remove caterpillars by hand and treat aphids with insecticidal soap.
- Willow anthracnose, scab and rust: Brown-black leaf spots, blackened shoot tips or orange pustules, mostly in wet springs. Remove affected leaves and shoots, keep good air circulation and avoid wetting the foliage in the evening.
- Branch die-back: Willows regularly lose individual branches, especially thin, shaded ones. Keep the canopy open to light, cut dead wood back to healthy tissue and grow replacement shoots.
- Root rot: Despite their thirst, willows rot in stagnant water. Use a free-draining soil and never let the pot stand permanently in water.