Sweet Pea Shrubs (Polygala)

How to choose a sweet pea shrub

The Sweet Pea Shrub, Polygala x dalmaisiana, is the classic garden hybrid: a rounded shrub of a metre or more with grey green leaves and purple flowers through most of the year. The Little Polly Sweet Pea Shrub is a selection of the same hybrid for gardens that want a neater plant. The Dwarf Sweet Pea Shrub is a dwarf form that suits low borders, edging and pots.

The Fairy Lights Sweet Pea Shrub belongs to a different species, Polygala chamaebuxus, a low spreading evergreen from the mountains of Europe with two toned flowers of purple pink and yellow. It is a small plant for cool climates, rockeries and containers, not a substitute for the larger shrubs.

A note on weeds: the species Polygala myrtifolia is an environmental weed in parts of southern Australia, particularly in coastal bushland. Compact garden selections are the ones to plant, and any polygala should be kept out of bushland. Do not dump prunings or old plants in reserves.

Where sweet pea shrubs grow

The shrubby polygalas suit temperate, Mediterranean and subtropical climates. They want full sun or light shade and soil that drains freely, and they do well in sandy soil. They tolerate wind and salt air, cope with dry periods once established and take light frost. Heavy, wet soil shortens their life.

They are useful as low informal hedges, fillers in mixed borders and tub plants on sunny terraces. For more ideas see our plants for coastal areas, low maintenance shrubs and evergreen shrubs.

Planting and spacing

Plant in a sunny position. Improve sandy soil with a little compost, and raise the bed if the soil is heavy. Set the plant at the same depth as it sat in the pot and water in well. Space dwarf forms 50 to 60 centimetres apart for a continuous low border, and allow about a metre between the larger shrubs. Fairy Lights spreads slowly, so plant it 30 to 40 centimetres apart in a rockery or as an edging. Mulch after planting, keeping it clear of the stems.

Care basics

Water regularly for the first summer, then only during long dry spells. Feed lightly in spring with a slow release fertiliser. The main job is pruning: trim all over after each main flush of flowers, taking off the tips, to keep the shrub dense and well covered with leaves to the base. Regular light trimming is better than one hard cut, as old bare wood can be slow to reshoot.

Sweet pea shrubs are quick growers and not especially long lived. Expect several good years, more with regular trimming and good drainage, then replace plants that become woody and open.

Common questions

Is sweet pea shrub a weed?

The wild species Polygala myrtifolia is an environmental weed in parts of southern Australia. Plant compact garden selections and keep any polygala out of bushland.

When do sweet pea shrubs flower?

The shrubby garden forms flower for much of the year in mild climates, with the heaviest display in spring.

Do sweet pea shrubs grow near the coast?

Yes. They tolerate salt air, wind and sandy soil, which makes them a common choice for seaside gardens.

How do I keep a sweet pea shrub compact?

Tip prune lightly after each flush of flowers. Frequent light trims keep the plant dense without cutting into old wood.