11 November 2009
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Cranesbill, Geranium

Hardy geraniums provide a long burst of summer flowers in a superb range of colours. There's at least one variety for every garden, whether small, large, dry, damp or shady. And they mix well with all kinds of plants.

Recommended varieties

Geraniums were brought to Britain in the 16th century. They were originally grown in physic gardens, but quickly found their way into ornamental ones. Don't confuse them with the indoor pelargoniums, which are completely different and don't survive outdoors in winter.

Geraniums range from the low-growing kind for the front of a border, which flop on the grass, to the tall, upright kind.

G. 'Ann Folkard': after a spring burst of yellowish-green leaves, the sprawling stems start snaking across the soil and produce a strong summer show of magenta flowers with a black eye. Keep other smaller plants at least 1m (3ft) away or they'll get smothered. It's been given the Royal Horticultural Society's (RHS) Award of Garden Merit (AGM).

G. clarkei 'Kashmir White': with a long flowering period, it spreads quickly by underground rhizomes, popping out of the ground with its soft-pink-veined white flowers. This has also been given the AGM.

G. 'Johnson's Blue': immensely popular, it's smothered in mid-blue flowers from early summer to autumn. The finely divided foliage makes a dense clump in sun or partial shade. It's received the AGM.

G. phaeum: it's called mourning widow because the late spring and early summer self-seeding flowers are dark maroon and sultry. This plant grows well in shady places. G. phaeum 'Variegatum': has white-margined leaves.

G. pratense 'Mrs Kendall Clark': the wild meadow geranium, often found on roadside verges in southern England, has given rise to many forms. They're popular in sunny summer borders and grow 90cm (3ft) high. The old-fashioned G. pratense 'Plenum Violaceum' is double-flowered and blooms for a remarkably long time in summer. Both have been given the AGM.

G. psilostemon: one of the best and most striking geraniums, it needs rich soil to reach 90cm (3ft), and stands erect with lipstick-magenta flowers and a black eye. It's received the AGM.

G. renardii: the white flowers are veined with violet and appear from early summer above dense mounds of soft, sage-green, crinkled leaves. They make neat clumps at the front of a border or rock garden, being just 30cm (12in) high. It's been given the RHS' AGM.

G. sylvaticum 'Album': a white form of a British native, it flowers from late spring - given a cool, shady position. 'Mayflower' has violet-blue flowers. Both have received the AGM.

G. wallichianum 'Buxton's Variety': one of the last geraniums to emerge in spring, it quickly makes a sprawling, leafy clump, and has sky-blue flowers with white veins from summer to autumn. It's been given the AGM.

Growing tips

Site and soil preferences

Geraniums thrive in most soils, unless extremely waterlogged. While most grow in sun or dappled shade, others, such as G. phaeum and G. nodosum, thrive in deep shade.

Buying and planting

When buying geraniums, look for plants with plenty of leaves and shoots growing from the base. They can be planted at any time, but spring and autumn are ideal.

Planting associations

With specimens in shades of blue, pink, maroon and white, geraniums can be used in most colour schemes. One of their most useful qualities is an ability to form attractive, floriferous ground cover, even in the deepest shade. The best for this is G. macrorrhizum, which spreads by underground rhizomes and eventually forms an impenetrable mat that suppresses most weeds.

Cutting back

Most species die down in the autumn, when their old foliage and stems can be cut back to encourage a crop of fresh leaves in spring.

Feeding

A light scattering of a general fertiliser around plants in the spring keeps them happy all year.

Propagation

Most geraniums are easily propagated by division in the spring. But some, such as G. wallichianum 'Buxton's Variety', pose problems because the stems tend to go back to a small rootstock. The best solution is to propagate by seed, although this may produce offspring that vary slightly from the parent.

Geraniums with trailing stems, such as G. 'Ann Folkard', can be propagated by spring cuttings using the new side shoots. Remove each cutting above a node, where the leaves are attached, and cut about 2.5cm (1in) off the bottom to leave a bare stem. Then insert the stems in pots or trays of cuttings compost. The cuttings should be watered in, covered with polythene and placed in a shaded glasshouse or cold frame.

Problem solver

Hardy geraniums are trouble-free and resist most pests and diseases. White, powdery mildew may occasionally affect G. pratense later in the year, but cutting back the plant to ground level will generally result in a fresh crop of mildew-free leaves within a few weeks.