Gardens
RHS Garden Rosemoor
Plant of the Month: June
Name: Geranium maderense
Common name: Giant herb Robert
Family: Geraniaceae
Vital statistics
Height and spread: 1.2-1.5m (4-5ft) x 1.2-1.5m (4-5ft)
Form: Evergreen perennial but treated as a biennial
Soil: Moderately fertile, well-drained
Aspect: Full sun or partial shade
Hardiness: Half hardy
Geranium maderense @ Rosemoor
The best place to see this fantastic plant at its best at Rosemoor is in the Old Kitchen Garden, where it has the shelter it needs to thrive. It has become noticeable over the last few years how much better our plants are surviving the Devon winters, and we have a number of plants that have now established themselves over several years with hardly a backward glance.
Geranium
Geranium comes from the Greek word geranos, a crane, in allusion to the long beak of the carpels.
The genus contains approximately 300 species of annuals, biennials and perennials, often confused with the genus Pelargonium, which is frequently, though incorrectly, known as Geranium.
Cranesbills are generally long-lived, undemanding plants found in all except very wet areas in temperate regions.
The leaves are attractive, usually palmate with toothed lobes, sometimes aromatic or interestingly marked and some colour well in autumn.
The flowers are simple, flat, five-petalled in white, pink, purple or blue, followed by long, narrow fruit.
G. robertianum, known as herb Robert, and other species, have a long history in herbal medicine.
The shorter geraniums are good for rock gardens, trailing or spreading species can be used effectively as ground cover and taller, clump-forming species and hybrids are suitable for borders.
Geranium maderense
The name maderense means “of Madeira”, which is where this species, the largest geranium, is found. It has a shrubby habit, and although a perennial it is usually short lived and behaves as a biennial.
It has rosettes of five to seven deeply lobed and divided, bright green leaves up to 20cm (8in) long.
From spring to late summer, flat, pinkish-magenta flowers are produced 4cm (1.5in) across. The colour is shaded, paler pink at the circumference becoming deeper magenta towards the centre, with dark veins and red anthers. They are produced on hairy, purple-stemmed flowerheads.
AGM
The RHS Floral A (Herbaceous Plant) Committee awarded Geranium maderense an Award of Garden Merit and described it as: Robust but short-lived evergreen perennial or biennial to 1.5m, with attractively dissected leaves to 20cm long and large panicles of purplish-pink flowers 4cm across, with darker centres.
Cultivation
In the open, grow in moderately fertile, well-drained soil in full sun or partial shade. Remove old flowers and leaves to encourage new growth.
Under glass, grow in loam-based John Innes no 2 compost, with sharp sand added, in bright, filtered light. Water freely and apply a balanced liquid fertilizer, monthly, during the growing season.
Geranium maderense may be damaged by vine-weevil and sawfly larvae, slugs and snails.
Viruses and downy and powdery mildew may cause problems.
Propagation
Sow seed at 13-18°C (55-64°F) in spring.
Divide in spring.
Take basal cuttings in early or mid-spring and root with bottom heat.