Tree Wisteria Bolusanthus speciosus

Tree wisteria is a slender South African tree hung with drooping sprays of violet blue pea flowers in spring, the wisteria effect delivered on a single trunk instead of a pergola. Its foliage is fine and pinnate, almost feathery, so the shade beneath stays light and grass or underplanting still grows there. It is used as a small feature tree where a big canopy would not fit: courtyards, pool surrounds, front gardens, and the awkward strip beside a driveway where a larger tree would eventually cause trouble.

Heat, drainage and the first winters

It comes from hot, seasonally dry country in southern Africa and it wants heat and soil that drains freely. Sandy loam, gravelly ground and raised beds all suit it, while heavy clay holding water through winter does not, and it copes with dry spells once it has settled in. Moderate water through the establishing years is enough. It performs well in Perth, Brisbane, Adelaide and warm inland districts, and in cooler gardens it is worth giving it a north facing wall and shelter from cold wind. Dig the hole no deeper than the root ball and backfill with the soil that came out of it. The roots are well behaved and the crown stays compact, which is what makes it usable close to paving.

The failure mode is frost on a young tree. Established trees take light frost, but a newly planted one can be cut back to the ground by a hard winter in a cool inland garden. Plant in spring rather than autumn so it has a full warm season in the ground first, and cover or wrap it through the first couple of winters anywhere frost is likely.

A small feature tree against the big natives

Nothing else in this range fills the same slot. Modong and swamp she-oak are the other trees here, and both are large, litter dropping shelter and revegetation species for open ground, paddock edges and wet sites. Tree wisteria is the opposite brief: a compact, well mannered specimen for a small garden, grown for flower rather than shelter, and safe to plant near paving and a pool. If your site is a large block with room to spare, take a paperbark or a she-oak. If it is a courtyard and you get one tree only, this is the one to plant, and it is the only one of the three you would choose for flower.

Shaping a young tree

Prune once flowering finishes in late spring, while the tree is young and the cuts are still small. Select a single leader, remove crossing branches, and lift the canopy gradually to the clearance you want underneath, then keep pruning to a minimum, because the naturally narrow shape needs very little help from you. Feed in early spring with a complete fertiliser, water it in and mulch out towards the drip line, keeping the mulch off the trunk. Stake a newly planted tree loosely for its first year in a windy position and take the stake off once the trunk thickens.

Choosing a size

This plant is supplied in one size, 300mm, at $139.00 per plant. The size shown is the pot it arrives in, which is the rootball, not the height of the plant. Not sure which to choose? Read our guide to when to plant in Australia.