Prostanthera herb and seeds

These highly attractive aromatic shrubs are natives of Australia. I have fallen in love with these most generous of flowerers. When exhibiting one in flower at the Chelsea Flower Show some member of the public fell in love with it in equal measure and tried to liberate it from my display! I can find no historical references other than in the RHS Dictionary of Gardening, which states that the generic name, Prostanthera, comes from 'prostithemi' to append, and anthera, meaning 'anther', the pollen bearing part of the stamen. This therefore alludes to the appendages usually borne by the' anthers.

Species

Prostanthera cuneata

Evergreen half-hardy perennial. Ht and spread 60- 90cm (2-3ft). Very attractive white flowers with purple spots that look rather like little orchids; late spring, early summer. Round, dark green, slightly leathery and shiny, mint-scented leaves. Can withstand a minimum temperature of-2°C (28°F).

Prostanthera ovalifolia

Evergreen tender perennial. Reaches a height and spread of 1.2m (4ft) in its native country. Attractive purple flowers appear on short leafy racemes throughout the spring and summer. Dark green aromatic leaves. Can only withstand a minimum temperature of 5°C (41°F).

Prostanthera rotundifolia rosea

Evergreen half-hardy perennial. A small tree that reaches a height of 3m (10ft) in its native country; in cooler climates it’s a lot smaller. Pretty mauve/purple flowers in spring that last a long time. The dark green leaves (not as dark as P. cuneata) are round and mint scented. Can only withstand a minimum temperature of 0°C (32°F).

Prostanthera sieberi

Evergreen tender perennial. Reaches a height of 2m (6ft), spread 1.5m (5ft) in its native country; in cooler climates it is a lot smaller. The green leaves are small (but larger than the other species mentioned), oval, and coarsely toothed, with a strong mint scent when crushed. Can only withstand a minimum temperature 5°C (41 °F).

Cultivation

Propagation

Cuttings

Take cuttings either in spring or late summer. Use the bark, peat, grit mix of compost. When the cuttings are well rooted, 8-12 weeks, pot up again using the bark, peat, grit mix and keep in containers for the first year.

Pests and Diseases

Over watering young plants is a killer.

Maintenance

Spring: Take cuttings.

Summer: Cut back after flowering only if necessary.

Autumn: Protect from frosts.

Winter: Protect from hard frosts and excessive water.

Garden cultivation

In cool climates with persistent frosts they are better grown in a container However if your climate is mild, plant out in the spring in a warm corner, in a lime-free, well-draining soil at a distance of 60-90cm (24-35in) apart. Rain combined with frost is the killer in winter. If you want to make a low I hedge out of Prostanthera cuneata then plant specimens 45cm (18in) apart.

Harvest

Pick leaves in the summer after flowering for drying and inclusion in potpourris.

Container growing

This is a real crowd puller when in flower, and even when not, makes a most attractive aromatic plant. Use the bark, peat, grit mix of compost. Keep young plants on the dry side, but water freely in the growing season.

Medicinal

I am sure that a plant that gives off as much scent, and has obviously so much oil in the leaf (P. cuneata), will one day have some use.