Family: Geraniaceae
Common Name: Geranium

The plants that most of us call geraniums in fact belong to the genus Pelargonium. Most of the 250 species are native to South Africa, while the true Geranium species, or cranesbill geraniums, originate from a number of countries, including Europe. Several species and numerous hybrids of Pelargonium are old garden favourites and are also popular as potted plants.

There is quite a range of sizes and growing habits amongst these plants and some are grown for their foliage value alone. In warm climates, these plants grow rapidly and quickly become rangy but, in cooler regions, they grow more slowly and are ideally suited to bedding schemes, edgings and container-growing. They continue to be amongst the most popular and best known of plants.

Species

Pelargonium x donesticum, Lady Washington pelargonium, Martha Washington geranium, regal geranium, has a shrubby habit. The leaves are fluted and slightly hairy, with stems becoming woody with age. The large, velvety flowers usually have a distinct blotch or feathering on the petals. The colour range Includes white, salmon, apricot, crimson and various shades of mauve or purple.

P. x hortorum is the garden or zonal geranium. The rounded, lobed leaves mostly have concentric zones of colour, forming the characteristic horse-shoe mark. Some varieties are grown mainly for their very decorative, colourful foliage, and many of these have fairly insignificant tlowers. The blooms are borne in rounded heads made up of many individual flowers that may be of single, double or rosebud form. The colour range covers white through pink, red, apricot, lavender and magenta, and includes some bi-colours.

P. peltatum, the ivy geranium, has a trailing or climbing habit. The slightly fleshy leaves are ivy shaped and not zoned. Free-flowering, these geraniums come in a lovely colour range, including white, pink, red, lilac and several outstanding bi-colours. Scented-leaf geraniums, grown for their aromatic foliage and diverse range of form and leaf shape, include P. graveolens, rose-scented geranium, P. odoratissimum, apple-scented geranium, and the peppermint geranium, P. tomentosum. These are best grown as greenhouse or conservatory pot plants in frost-prone climates. Grow them in intermediate conditions.

Cultivation

In frost-prone climates, grow as summer bedding plants or as greenhouse pot plants. For best results, grow in locations which receive full sun all day. The soil must be very free draining but need not be rich. Acid soils should be limed before planting, by adding 100 grams of lime or dolomite per square metre (3½ oz per square yard) before planting. Geraniums need regular water to establish but, once established, they should be watered only as the soil dries out. It is better to underwater than over-water.

Slow-release fertilizer or pelletted poultry manure may be applied in spring, but excess fertilizer, especially high-nitrogen types, can result in weak, soft growth. Plants should be well maintained by cutting off spent flower heads and by regular tip pruning. Prune plants fairly hard in early to mid-autumn. Propagate from tip cuttings taken at almost any time of year. Pelargonium grown as pot plants under glass should be grown in well-drained, soil-based potting compost. Ensure maximum light and an airy atmosphere, but shade the plants from direct strong sun.

Climate

Zone 10. Pelargonium prefers warm to hot, dry climates.