The Robinia genus consists of about 20 species but it is Robinia pseudoacacia that is commonly used for bonsai. R. pseudoacacia is a fast-growing, deciduous, broadly columnar tree with usually spiny shoots.
Pinnate, dark green leaves up to 30cm long are divided into 20+ lance-shaped, blunt leaflets. In May-June, R. pseudoacacia bears fragrant white flowers, 2cm long in pendant racemes, to 20cm long.
Native to the USA, False Acacia are a pioneer species that will cope with adverse growing conditions where it can reach heights of up to 25metres.
BONSAI CULTIVATION NOTES
POSITION: Full sun. Though fully hardy, Robinia are sensitive to early frosts in Autumn and need protection from these. Once the tree has lost it’s foliage and entered dormancy, it only requires frost protection when temperatures drop below -10°C. Provide shelter from very strong winds to avoid the relatively brittle branches snapping.
FEEDING: Feed fortnightly during the growing season. As a member of the pea family (Leguminosae), Robinia are able to absorb nitrogen from the atmosphere and do not require high nitrogen feed during the early part of the growing season.
REPOTTING: Every second year in Spring, use basic soil mix.
PRUNING: Trim new growth back during the growing season, ‘leaves’ consisting of up to 20 leaflets can be reduced back to as little as 3 or 4 leaflets to retain shape. Hard pruning should be carried out after leaf-fall in Autumn to avoid excessive sap bleeding. Ensure any suckers that appear from the base are removed immediately unless required.
PROPAGATION: Sow seed outside in Autumn. Hardwood cuttings in Autumn, layering in Spring.
PESTS AND DISEASES: Trouble free.
STYLING: Informal upright forms with single or multiple trunks in medium to large sizes.