Birch

Fertilizing

For established trees, delay fertilizing until 3-4 weeks after spring growth begins to prevent overly coarse development. Use organic fertilizers like liquid seaweed, kelp, or fish emulsion that support beneficial microorganisms in the soil. For developing trees needing vigor, fertilize every two weeks during growing season. Once the first partial defoliation is complete, begin fertilizing every 6-8 weeks. Avoid fertilizing during dormancy as winter salts can damage roots.

Hold back on fertilizer if growth becomes leggy or you want to maintain smaller leaves. Remember that birch can thrive without heavy feeding - fertilizer is a bonus rather than necessity. The choice between liquid and solid fertilizers comes down to preference, though many practitioners use both for optimal results.

Placement

Birch requires full sun exposure and must be grown outdoors year-round. Rotate the tree regularly so all areas receive equal light. While extremely frost hardy, provide protection when temperatures drop below -7°C to prevent twig die-back. During intense summer heat, some midday shade may be needed to prevent leaf burn. The bark must receive direct summer sunlight to develop its characteristic white coloring, especially in young trees still developing their mature bark.

Pruning

The birch requires careful timing with pruning to prevent dieback issues. Prune between spring leaf emergence and late summer, avoiding cuts during dormancy. When pruning back shoots, cut to 2-3 leaves after growth hardens off. For structural pruning of large branches, only prune during active growth periods and seal wounds well as birch bleeds heavily. Never cut large branches flush to the trunk - leave a stub initially to prevent dieback spreading down the trunk. The stub can be removed after 1-2 years once the tree compartmentalizes the wound.

Partial defoliation can be performed on healthy trees by removing 70-80% of leaves to stimulate fresh growth and increase ramification. This is especially helpful for reducing leaf size on trees in development. Always keep some foliage to maintain energy production.

Repotting

Repot every 2-3 years in early spring as buds begin extending but before leaves fully emerge. Use a well-draining soil mix - professional-grade akadama is ideal but expensive. Alternative mixes using lava, pumice and pine bark also work well. Wait until buds show green before root pruning, as working with fully dormant trees increases risk. Remove about 1⁄4 of roots when repotting.

Apply a thin layer of sphagnum moss/green moss topdressing mix (1:1 ratio) after repotting but before watering. This protects the soil, improves water distribution, and encourages beneficial organisms. Water thoroughly after repotting but then allow soil to dry significantly between waterings to promote healing and prevent rot.

Watering

The birch is a thirsty species requiring abundant water during summer growth. However, avoid constant soil saturation - the substrate should dry somewhat between thorough waterings. A shallow water bowl can help during intense heat if you're away during the day. In winter, maintain slight moisture but reduce watering significantly. After repotting, allow soil to dry noticeably between waterings to encourage root healing and prevent rot. Consider your local climate and the tree's specific needs when establishing a watering routine.

References

Bonsai Empire Guide to Birch Bonsai4me Species Guide Bonsaiable Comprehensive Birch Guide