Fertilizing
Feed every 2 weeks from spring to late summer with a balanced liquid bonsai fertilizer, or use a solid organic fertilizer once a month. Tamarisk is not a heavy feeder, and too much fertilizer only produces long, coarse shoots.
- Switch to a lower-nitrogen fertilizer in late summer.
- Stop feeding in early autumn so the shoots can ripen before winter.
Placement
Keep tamarisk outdoors all year in full sun; it tolerates heat, drought, wind and salty coastal air. In shade the inner foliage thins out and dies back, and the tree flowers poorly.
It needs a cold winter dormancy. It is very hardy in the ground, but in a pot protect the roots below -10°C (14°F) in a cold frame or unheated shed, or by burying the pot.
Pruning
Time pruning to the flowering habit of your species. Spring-flowering species such as Tamarix parviflora bloom on last year's wood and are pruned right after flowering, while summer-flowering species such as Tamarix chinensis and Tamarix ramosissima bloom on new shoots and are pruned in early spring before growth starts.
- Cut back hard once a year, as tamarisk grows fast and otherwise becomes tangled.
- During the growing season, trim long shoots repeatedly to keep the foliage dense.
- Remove crossing branches and thin the interior so light reaches the inner shoots.
- To create a more tree-like shape, remove the lowest side branches in late winter or early spring, leaving the branch collar intact.
Weeping styles are made by wiring the long new shoots downwards while they are still flexible, from late spring to summer. The wood stiffens quickly, so check the wire often.
Repotting
Repot young trees every 2 years and older ones every 3 years, in spring as the buds start to swell. Tamarisk roots vigorously and tolerates moderate root pruning of about a third.
Use a free-draining bonsai mix of akadama, pumice and lava or grit. It is unfussy about pH and tolerates neutral to slightly alkaline soil, but not soil that stays wet.
Watering
Tamarisk is drought-tolerant in the ground, but in a small bonsai pot it still needs regular water in summer. Water thoroughly as soon as the top layer of soil has dried, which may be daily in hot weather.
Avoid waterlogged soil, which quickly rots the roots. In winter, when the tree is leafless, water only enough to keep the root ball from drying out.
Seasonal care
- Spring: Prune summer-flowering species before growth starts, repot as the buds swell and start feeding every 2 weeks. Spring-flowering species bloom now; prune them right after flowering.
- Summer: Keep the tree in full sun, water regularly and trim long shoots to keep the foliage dense. Summer-flowering species carry pink plumes on the new shoots; wire weeping branches while they are flexible.
- Autumn: Switch to a low-nitrogen fertilizer in late summer and stop feeding in early autumn. The foliage turns yellow and the fine shoots are shed together with the leaves.
- Winter: Keep the leafless tree outdoors for its cold dormancy and protect the roots below -10°C (14°F). Water sparingly so the root ball never dries out completely.
Common problems
Tamarisk is tough; most problems come from too little sun or soil that stays wet.
- Bare, dying interior: Inner shoots die back when they get too little light. Keep the tree in full sun and thin the outer foliage regularly.
- Root rot: Soggy soil, especially in winter or in a poorly draining mix, rots the roots. Use a free-draining mix and water only when the top layer has dried.
- Long, untidy shoots: Fast growth, shade and overfeeding make the tree look shaggy. Trim repeatedly in summer and feed moderately.
- Scale and aphids: These sap-suckers sit on young shoots and leave sticky honeydew. Rinse them off and treat with horticultural oil.
- No flowers: The tree was pruned at the wrong time for its species or stands in too much shade. Check whether it flowers on old or new wood, prune accordingly and give it full sun.