Plant of the Month: August

Salvia patens Common name: gentian sage, blue-flowered sage, spreading blue sage Family: Lamiaceae Vital statistics Height and spread: 45-60cm (18-24in) spread 45cm (18in). Form: Perennial herb. Soil: Fertile, humus rich but well-drained. Aspect: Full-sun or partial-shade Hardiness: May be somewhat tender when young.

Salvia patens @ Wisley

The Canal border contains many tender perennials in pastels and more vibrant shades. Among them is Salvia patens and two of its cultivars, 'Cambridge Blue' and 'Chilcombe'. 'Chilcombe' is lavender blue and located near the Laboratory end. 'Cambridge Blue' is interplanted with both the species and a purple penstemon around one of the containers. The species is planted in a couple of bold groups down the border.

Salvia

This is a large genus of about 900 species of often aromatic, flowering plants containing mainly herbs and numerous sub-shrubs, of which many are tender to some degree. They include annuals, biennials, evergreen and herbaceous perennials, and shrubs. Some are rhizomatous or tuberous.

They originate from temperate and tropical parts of the world but not very hot and humid regions, and grow mainly in sunny places.

The usually square stems bear opposite pairs of simple to pinnate, toothed leaves. The two-lipped flowers are normally borne in whorls along the stems during late summer or early autumn.

Annual salvias, and perennials grown as annuals, provide brilliant colour for bedding, infilling or containers, for their flowers  colourful bracts. Common bedding salvias include cultivars of the scarlet sage Salvia splendens such as 'Scarlet King' which is compact, has dark green leaves and scarlet flowers. Some species like S. viridis (annual clary) are also popular if grown in light woodland or wildflower meadows, where they attract bees and other wildlife.

Several species have deliciously aromatic foliage, the most well-known being common sage, Salvia officinalis. Sage is a well-used culinary herb, often associated with pork dishes and famously used with onion in stuffing. S.sclarea (biennial clary) and S. viridis (annual clary) are also in wide spread cultivation as culinary herbs and for medicinal uses.

The name salvia is derived from the Latin 'salvare', meaning to save or heal, referring to the supposed medicinal properties of certain species.

Salvia patens

Salvia patens is a tuberous perennial herb with erect stems and toothed, hairy mid-green leaves 20cm (8in) long. It comes originally from Mexico. In midsummer to mid autumn it produces few-flowered loose sometimes branched, terminal racemes of gentian blue flowers, hence the common name of gentian sage. It can grow to a height of 45cm (18-24in) spread 45cm (18in).

The cultivar 'Cambridge Blue' AGM has light blue flowers and 'Chilcombe' has lavender blue flowers.

AGM

Cultivation

Under glass grow in well-drained, loamless or loam based potting compost in full light. Feed with a balanced liquid fertiliser monthly.

Outdoors, grow in light moderately fertile humus rich well drained soil, in full sun or partial shade.

Salvia patens can be treated like a dahlia: dig it up in the autumn and keep it dry and frost-free over winter.

Trim or lightly cut back shoots that spoil the symmetry. Dead head regularly.

Slugs and snails will attack young growth.

Propagation

Sow annual seeds at 16-18C (61-64F) in mid spring, and biennials in containers in a cold frame in summer. Alternatively, they can be sown in situ after the danger of frosts has passed.

Perennials should be sown in containers in a cold frame in spring. They may also be divided in spring. Basal or softwood cuttings can be taken is spring or early summer, or semi-ripe cuttings in late summer or autumn.