Oxalis: is well known to nearly every gardener, unfortunately as a weed more often than as an attractive rock garden plant. This does not mean you should avoid Oxalis, the species listed below will provide attractive foliage and in summer colourful funnel shaped flowers in white, pink, yellow or lilac. These plants will not become aggressively invasive, but unfortunately there are many species which will become rampant, so never introduce an Oxalis unless you know its growth habit. Varieties: The most popular rockery species is O. adenophylia, the basic details are height three inches, spread six inches and the flowering period is from June to July. The grey-green pleated leaves form a neat clump, the flowers are white with pink edging and veining. O. enneaphylla is even more restrained and even more attractive, white, pink and red varieties are available. O. laciniata is another choice species; the flowers are rich purple. The white-flowered O. magellanica is a prostrate creeper but is not invasive. Site and Soil: Requires well-drained soil in full sun. Propagation: Divide clumps in autumn.

Papaver: Dwarf Poppy is short lived but the ones below do produce self-sown seedlings without becoming invasive. These dwarf types look like miniature Iceland Poppies with petals in a wide range of colours and with the appearance of crinkled tissue paper. Varieties: A number of species which are native to the European Alps are grouped together and listed as P. alpinum (Alpine Poppy). The basic details are height six inches, spread four inches and the flowering period is May to August. White, pink, yellow or orange flowers are borne on short stalks above ferny grey leaves. An easy to grow plant unless the soil is heavy, but it blooms itself to death in two or three years. An alternative dwarf for the rock garden is P. miyabeanum (Japanese Alpine Poppy). Large, nodding yellow flowers are borne on six-inch stems. Site and Soil: Requires well-drained soil and thrives best in full sun. Propagation: Dislikes root disturbance, sow seeds in late summer where the plants are to grow.

Parahebe: is a semi-woody plant that grows less than twelve inches high and produces small white, blue or pink Speedwell-like flowers. These blooms are borne in loose clusters and appear in late summer and early autumn. Varieties: P. catarractae is an upright bush, the basic details are height ten inches, spread twelve inches and the flowering period is from August to October. The blooms are white with a crimson eye. P. lyallii is another species which is available from large garden centres and is an easier plant to grow. It is a spreading bush eight inches high, with leathery leaves and pink-veined white flowers in July and August. Another easy one, P. bidwillii, with pink-veined white flowers appear above a six-inch high rounded bush. Site and Soil: Requires well-drained soil and a sunny site. Propagation: Plant stem cuttings in early summer.

Penstemon: bear tubular, two-lipped flowers in large clusters in summer. The usual colours are pink or purple, but blue and white ones are available. The Penstemons are showy plants, but they do tend to be delicate. Varieties: The hardiest species is P. pinifolius, height six inches, spread twelve inches and the flowering period is from June to September. Dark orange blooms are borne above the needle-like foliage. There is much confusion over the naming of Penstemons. There is a group which grows about nine inches high with a spread of about twelve inches and produces lots of flowers in midsummer. Included here are P. roezlii (red), P. newberryi (pink or red) and P. menziesii (violet). A distinct species is the prostrate P. rupicola (three inches high) with crimson flowers. Site and Soil: Requires light, well-drained soil, thrives best in a sheltered site in full sun. Propagation: Plant stem cuttings in early summer.

Phlox: has numerous varieties and any one of these plants will provide you with a flat sheet of white, pink, blue, lavender or red flowers. Phlox will grace any rock garden. It is easy to grow and will cover rocks or tumble over walls, bearing masses of half-inch blooms in late spring or early summer. Varieties: P. subulata is one of the two basic species, height is four to six inches, spread eighteen inches and the flowering period is May to June. There are many named varieties, such as 'Scarlet Flame' (red), 'Vivid' (pink, compact), 'Temiscaming' (pale red, vigorous) and 'G. F. Wilson' (blue). The other basic species P. douglasii (Alpine Phlox) also has many varieties such as 'Apollo' (violet, compact), 'Crackerjack' (red) and 'Iceberg' (white). The height and spread of this species are similar to P. subulata, but the clumps are tidier and the flowers appear later. Other types include P. kelsyi 'Rosette' (violet-pink, miniature) and P. amoena variegata (bright pink, leaves in green and cream). Site and Soil: Requires well-drained, moisture-retentive soil and thrives best in full sun. Propagation: Plant stem cuttings in summer.

Pleione: Rockery Orchid is an especially satisfying plant to grow in the rockery. Cost is not a problem you will have to pay no more for a suitable Pleione than you would for some Primulas. The problems are that you will have to search through a number of catalogues to find a supplier, and you will need a sheltered site in a mild locality in partial shade. No specialist compost is needed just enrich the soil with peat and some sharp sand. Cover in the winter. There is a risk but you may well be rewarded with true Orchid flowers. Varieties: P. bulbocodioides (P. formosana) and its varieties are the Pleiones which are usually chosen for growing outdoors, height three inches, spread six inches and the flowering period is from April to May. The showy three-inch blooms bear narrow white, pink or purple petals and a large yellow or white central tube. Site and Soil: See above for details. Propagation: Plant detached bulbs in spring.

Polygonum: Rockery Knotweed bear tiny flowers in white, pink or red in clusters above the foliage. The growth habit is wide spreading and the flowers appear in spring or autumn depending on the species. Numerous species are sold for garden use and you must choose with care, most of them are far too invasive for growing in a rock garden. Varieties: Polygonum is sometimes listed as Persicaria. The pink-flowered P. affine 'Donald Lowndes' (height twelve inches, spread two feet or more, flowering period is June to October) is frequently recommend for rockery use, but you will have to keep it in check. P. vaccinifolium is the common rock garden type, height four inches, spread two feet and the flowering period is September to December. The pale pink flowers are borne on upright spikes and the leaves are tinged red in autumn. For something smaller choose P. tenuicaule, height four inches, spread twelve inches and the flowering period is March to April. The white flowers are borne on small upright spikes. Site and Soil: Requires well-drained soil in full sun. Propagation: Divide clumps in autumn or spring. Alternatively plant stem cuttings in autumn.

Potentilla: Rock Cinquefoil is popular in beds and borders as they are shrubby but generally too large for the rock garden. Still there are numerous species which are suitable and some are described below. These Rock Cinquefoils are generally mat-forming plants with the long period of flowering associated with their shrubby cousins, but sometimes without their free flowering habit. Varieties: P. 'Sunset' (eighteen inches high) is a compact variety of the Shrubby Potentilla P. fruticosa and useful for the larger rock garden. A typical rockery one is P. aurea (Golden Cinquefoil) height four inches, spread twelve inches and the flowering period is June to September. The flowers are yellow and appear above creeping stems. For yellow flowers on a small upright bush grow P. crantzii (six inches high). P. eriocarpa is becoming popular with lots of pale yellow flowers throughout the summer. P. nitida has silvery leaves, pink flowers and low-growing stems, but it does not flower freely. P. tonguei bears orange blooms with a red centre. Site and Soil: Requires well-drained soil in full sun. Propagation: Sow seeds in spring or divide clumps in autumn.

Primula: Rockery Primrose has hundreds of species and varieties suitable for the rock garden. There is a basal rosette of leaves and from this the flower-stalks arise, bearing Primrose-shaped blooms which may be pendant or upright. There are few general rules about cultivation. Most types require humus-rich soil, plenty of moisture during the growing season and a little shade during the day. But there are Primulas which thrive only when exposed to full sun and others which require shady and swampy conditions. Some will grow almost anywhere others need to be pampered. The Primulas chosen here are all relatively easy to grow and are suitable for outdoors. Varieties: Border types, such as the Common Primrose (P. vulgaris), Polyanthus (p. variabilis), Cowslip (P. veris) and the Drumstick Primrose (P. denticulata), are often planted in rock gardens. The fleshy-leaved Auricula (P. auricula) is an old favourite with a height of six inches, spread six inches and the flowering period is March to April. Large flowers are borne in clusters on top of the flower-stalks. P. juliae has a different growth habit; it is a low carpeter flowering from March to May. Well known hybrids include P. 'Wanda' (purple-red) and P. 'Lady Greer' (yellow). P. pubescens is the group name for many four to six inch high hybrids blooming from April to May. Several favourites belong here, P. 'Harlow Carr' (cream), P. 'Faldonside' (white-eyed pink), P. 'Mrs Wilson' (white-eyed purple) etc. P. marginata is a small plant flowering in April. The best known variety is 'Linda Pope' (mauve-blue). P. vialii is the odd one out attaining a height of twelve inches and flowering from June to July. P. rosea (six inches high) needs very moist soil, P. sieboldii needs a peat bed and P. edgeworthii is very early but needs winter protection. The baby is P. minima only two inches high with a spread of five inches. Site and Soil: Well-drained, moisture-retentive soil in light shade is the usual requirement. Propagation: Plant stem cuttings in summer or divide clumps after flowering.

Pulsatilla: Pasque Flower grows wild on the meadows and downs over limestone. In the garden it is easily raised from seed and is a welcome sight on any rockery at Easter. In spring the flower-stalks push up through the earth, each one crowned by a silky bud. The buds open into three-inch wide cup-like flowers and later into flat stars. The flowers are followed by ferny foliage and then by attractive silky seed heads. Varieties: The Pasque Flower is P. vulgaris (Anemone pulsatilla) height nine inches, spread twelve inches and the flowering period is from April to May. The flower colour is pale purple but you can buy varieties in white (alba) or red (rubra). P. vernalis is even more attractive, the flowers are pearly white inside, flushed purple on the outside with a prominent boss of golden stamens. It grows about six inches high. P. alpina is a taller white flowering Pulsatilla. Sulphurea is a yellow flowering variety. Site and Soil: Requires well-drained soil and a sunny site. P. vulgaris and P. vernalis need alkaline soil. Propagtion: Sow seeds in summer.

Ramonda: hates prolonged direct sunlight. The place for it is on the north side of a rock garden and as with the closely-related Haberlea it should be planted sideways in a crack or crevice. The reason for this sideways planting is that it cannot tolerate water standing in the crown in winter. Varieties: The easiest species to grow and to find is R. myconi which grows wild in the Pyrenees. The basic details are height five inches, spread nine inches and the flowering period is from April to May. The evergreen leaves are rough and crinkled and the large flat-faced flowers are lavender with a boss of golden stamens. The varieties 'Alba' (white), 'Rosea' (pink) and 'Coerulea' (blue) are available. R. nathaliae is smaller but similar to R. myconi. R. serbica differs by having purple stamens. 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.