Frankenia: Sea Heath is an appropriate name for this carpeting plant, it looks like Heather when not in bloom and its natural home is the seaside. One of the species grown (F. laevis) is found growing wild in coastal areas. Frankenia is a prostrate shrubby plant with wiry stems and tiny leaves. In summer small pink flowers appear above the foliage, each one bearing five petals around a yellow centre. In autumn the foliage is often tinged with reddish tones. Varieties: F. laevis is the smaller of the two species offered for sale. The prostrate reddish stems bear small narrow leaves with inrolled edges; this foliage is green and slightly downy. Solitary pink flowers, about a quarter inch across, appear in July and August. F. thymaefolia is easier to obtain and to grow. This native of Spain and Morocco differs in a number of ways. The flowers are larger, more numerous and are borne in clusters. The plant grows about three inches high. Site and Soil: Requires well-drained open soil, thrives in full sun. Propagation: Divide clumps or plant cuttings in summer.

Gaultheria: Wintergreen is one of the smaller species and is an excellent choice if you want an evergreen carpeter which bears bell-like flowers in summer and showy berries in autumn. Don't bother with Gaultheria, however unless you can provide it with acid, humus-rich soil in a partly shaded position. Varieties: The best-known Gaultheria is the Partridge Berry (G. procumbens). The spreading branches bear shiny, dark green leaves and this neat mat grows about six inches high. In July the pink-flushed white blooms appear and these are followed by bright red berries and reddish foliage in autumn. G. cuneata and G. miqueliana grow twelve inches high and bear white flowers which turn into white berries. G. nummularoides is quite different, the leaves are downy rather than leathery and it rarely grows over three inches high. The white or pink flowers are succeeded by blue-black berries. Site and Soil: Requires well-drained acid soil in partial shade. Propagation: Plant stem cuttings in summer.

Genista: Broom generally has wiry stems, tiny leaves and a mass of yellow flowers in June. Genista species may be evergreen or deciduous, spiny or thornless and heights range from two inches to twelve feet. All bloom freely if given plenty of sun and no food. Fertile soil reduces flowering. After flowering, invasive plants can be kept in check by cutting back stems which have borne blooms, but do not prune into old wood. Varieties: The most popular one for the rock garden is G. lydia, a spreading shrub growing about two feet high. Its arching stems are covered with golden yellow flowers in May and June. G. hispanica (Spanish Broom) is about twelve inches high, densely branched and spiny species which is excellent for groundcover. G. pilosa is a prostrate thornless species; G. pulchella (two inches) is even shorter. G. sagittalis is unusual, the young stems are flattened and winged and the bright yellow flowers are borne in terminal spikes. Site and Soil: Requires well-drained open soil in full sun. Propagation: Sow seeds or plant stem cuttings in summer.

Gentiana: is the queen of the alpines and creates a truly impressive rock garden. The blue trumpets can provide colour from May to October if you choose a selection of spring-summer and autumn-flowering types. Unfortunately most Gentians are rather temperamental and cannot be regarded as 'grow anywhere' plants. You should always check the likes and dislikes of a particular species before you buy it, and even then it can be flower-shy for no particular reason. Lime is a problem, spring flowering types may either tolerate or require it, but the autumn flowering Gentians cannot stand it. All demand free-draining but not impoverished soil. Add peat before planting firmly in spring. Varieties: The easiest one to grow is the summer flowering G. septemfida which gives a good display of one to two inch long purple-blue trumpets in any sunny well-drained spot. The basic details are height nine inches, spread twelve inches, flowering period July to August. The popular G. acaulis (Trumpet Gentian) is a smaller plant (three inches high) and blooms earlier (May to June), but its flowers are much more eye-catching, three inches long almost stemless trumpets standing upright above the glossy oval leaves. Unfortunately it is unpredictable, in some situations it will not bloom and nobody knows why. If your plant is flower-shy, simply move it to another spot in autumn. G. verna is another spring-flowering Gentian, height three inches, spread six inches, flowering period is May to June. Its starry flowers are bright blue, an attractive evergreen which is unfortunately short-lived. The most popular autumn flowering Gentian is G. sino-ornata, height six inches and spread twelve inches; flowering period is September to October. The two-inch long trumpets are bright blue with pale green stripes. For many experts the white-throated G. farreri is the best of all. Site and Soil: Well-drained soil is essential thrives in sun or light shade. Propagation Divide clumps in spring or midsummer.

Geranium: Rockery Cranesbill are low growing perennials which die down in winter and then produce divided or lobed leaves in spring and bowl shaped flowers in summer. The foliage may be green or grey and the white, pink or red flowers are usually prominently veined. All are easy to grow as long as the site is free draining and not too shady. Watch out for slugs. Varieties: G. cinereum is an attractive species, height six inches, spread twelve inches, flowering period is May to August. It is best known through its variety or hybrid G. 'Ballerina'; this plant has ashen-grey foliage and large pink flowers. There is a white type ('Album') and crimson one (G. subcaulescens). G. dalmaticum reaches the same height and spread as G. cinereum and its varieties, but the flowering period is shorter (June to August) and the pale pink flowers are not veined. Site and Soil: Any well-drained soil, thrives best in full sun. Propagation: Divide clumps in spring.

Geum: Alpine Avens Most of the ordinary Geums, such as Mrs. Bradshaw, are too tall for the rockery, but there are a few dwarfs which are excellent for filling planting pockets and should be more widely grown. They are true alpines, growing wild in the Swiss Alps. The flowers are large, usually yellow, and bear a prominent mass of stamens at the centre. These Rose-like blooms are followed by fluffy seed heads. Varieties: G. montanum produces clumps of rough and wrinkled leaves, and in summer a mass of golden yellow flowers on short stalks. The basic details are height nine inches, spread twelve inches; flowering period is May to July. It is an easy and reliable plant to grow, but G. reptans is not. This temperamental Geum produces long Strawberry-like runners which spread out, producing rosettes of leaves where rooting takes place. Bright yellow flowers, two inches across, appear on six-inch stems. A much better choice is its hybrid G. 'Borisii', clump forming, easy to grow and with masses or orange flowers all summer long. Site and Soil: Any well-drained soil, thrives best in full sun. Propagation: Sow seeds or divide clumps in spring.

Gypsophila: Baby's Breath has narrow greyish leaves and forms clouds of tiny white or pink flowers in summer. The most popular one is G. repens which looks like a scaled down version of the herbaceous border Gypsophila. It is ideal for trailing over rocks, and like the other dwarf species it is both hardy and easy to grow. Gypsophilas are lime lovers but an alkaline soil is not essential. Varieties: The basic details of G. repens are height six inches, spread two feet, flowering period is June to August. It is quick growing, the carpet of stems of grey-tinged foliage soon spreading over quite a large area. It is usual to grow a named variety. 'Dorothy Teacher' is a good compact form with bluish-grey leaves and pink flowers, fratensis and 'Letchworth Rose' are other single pinks and 'Rosea' is a double pink. For white flowers grow alba or 'Monstrosa'. Other species include the loosely cushioned G. cerastioides with its red-veined white flowers or the tightly cushioned G. arietioides. Site and Soil: Any well-drained soil, full sun is required. Propagation: Sow seeds or divide clumps in the spring.

Haberlea: is an attractive alpine, like its close relative Ramonda. It is quite different, as it will not grow unless the conditions are just right. This calls for acid soil in a shady spot and water must not be allowed to stand in the heart of the rosette of leaves in winter. The usual advice is to plant it sideways in a crack or between stones on the north facing side of the rockery. Varieties: The one you are most likely to find in the garden centre or catalogues is H. rhodopensis. Basic details are height four inches, spread eight inches and flowering period is May to June. There is a rosette of leathery toothed leaves and the stalks bear clusters of lilac flowers which are tubular and about one inch across. A white variety ('Virginalis') is available. H. ferdinandi-coburgii is larger and the lilac flowers are flecked with gold. Site and Soil: Requires well-drained but damp soil with little or no direct sun. Propagation: Divide clumps in autumn or plant leaf cuttings in summer.

Hebe: Veronica is a large genus of the evergreen shrubs from New Zealand, once grouped with Veronica and this still remains the common name. The usual pattern is a neat bush with either scale like or oval leaves and spikes of tiny white or blue flowers. They come in all sizes, but only the popular dwarfs are described here. Varieties: One of the best for the rock garden is H. pinguifolia 'Pagei". The bush is about nine inches high and the branches are clothed with greyish-green leaves. Between May and August floral spikes densely crowded with white flowers appear. H. 'Carl Teschner' is another popular Hebe. This prostrate plant with dark green leaves on near black stems has white-throated mauve flowers in June and July. H. 'Green Globe' is an eight-inch ball of tiny Box like foliage. H. epacridea is different. The stems are clothed with scale like leaves and these 'whipcord' branches bear white fragrant flowers in July. H. 'Boughton Dome' is another Whipcord Hebe, grown solely for its conifer like appearance. Site and Soil: Any well-drained soil in sun or light shade. Propagation: Plant stem cuttings in summer.

Helianthemum: Rock Rose Few plants can match the ability of the lowly Rock Rose to provide such a long lasting sheet of orange or yellow flowers during the summer months. Each flower lives for only a day or two, but new ones are borne in profusion between May and July. The spreading wiry stems become straggly and invasive if wrongly treated. Once the first flush of flowers has faded you must cut them back hard to prolong the life of the plant and to induce another flush. Varieties: Nearly all the Helianthemums grown in the rock garden are named varieties of H. nummularium. The basic details are height six to nine inches, spread two feet, papery flowers one inch across. The varieties may be single or double and the colours range from white to deep red. Well known ones include 'The Bride' (white), 'Fire Dragon'(orange) and 'Wisley Primrose' (yellow). The 'Ben' series ('Ben Hope', 'Ben Ledi' etc) are reputed to be the hardiest. H. alpestre (height four inches, spread twelve inches, yellow flowers) is an uncommon alpine relative. Site and Soil: Requires free draining gritty soil in full sun. Propagation: Plant stem cuttings in late summer.

Helichrysum: is a well-known annual grown for its everlasting flowers. The blooms are cut and dried for floral decoration. This plant has a number of dwarf perennial relatives and a few of them can be used for groundcover in the rock garden. The ones described below are suitable for growing outdoors. The Rockery Helichrysums are usually grown for their silvery foliage rather than their drab flowers. Varieties: The species you are most likely to find is H. bellidiodes, height three inches, spread eighteen inches, flowering period is June to August. It forms a mat of small woolly grey leaves which can be invasive if not kept in check. The white strawy-petalled flowers appear on short stalks. H. coralloides is grown for its curious coral-like appearance branched and gnarled stems covered with scale-like leaves. H. milfordiae has the most colourful blooms, red buds and large silvery-white flowers. Site and Soil: Any well-drained soil and full sun is essential. Propagation: Plant cuttings or divide clumps in summer.