Lithospermum: Gromwell is a groundcover plant with creeping stems and clothed with slender leaves. Masses of open-faced funnel shaped flowers appear in summer. The colour of the popular species and its varieties is Gentian blue. It is as bright as anything you will find in the summer rock garden. Lithospermum requires a sunny spot and humus-rich soil. Do not grow L. diffusum if your soil is chalky; choose instead the lime tolerant L. oleifolium. Varieties: The favourite Gromwell for the rock garden is Lithospermum diffusum (Lithodora diffusa), height six inches, spread two feet and the flowering period is June to September. Its outstanding feature is the pure blue of its flowers. Two named varieties rather than the species are grown 'Heavenly Blue' and 'Grace Ward'. Both are very similar despite the claim of obvious differences in some catalogues. L. oleifolium is quite different as the leaves are silvery-grey and the pink buds open into pale blue flowers. Site and Soil: Well-drained moist soil in full sun is essential. Propagation: Plant stem cuttings in midsummer.

Lychnis: Dwarf Campion is generally too tall for the rock garden and most of them belong in the herbaceous border, but there are a few dwarfs. The most popular one (L. alpina) is a tiny plant which is easy to grow in the cracks between paving stones. It is not difficult as long as the land is reasonably fertile. Unfortunately it is not long lived but the plants are easily raised from seed. Varieties: The usual Lychnis in the rockery is L. alpina, the Alpine Campion, which is sometimes listed as Viscaria alpina. The basic details are height four inches, spread four inches and the flowering period is May to July. The flower stalks are just a couple of inches high and each one is crowned with a group of pink flowers. For other colours choose the variety 'Alba' (white) or rosea (deep pink). The other dwarf Campions are taller. L. viscaria 'Splendens Plena' is a showy plant for the larger rock garden with heads of crimson double flowers on twelve-inch stalks. L. Flos-jovis bears its carmine flowers on eight to twelve inch stalks above grey-felted foliage. Site and Soil: Requires well-drained soil, thrives best in full sun. Propagation: Sow seeds in early spring.

Lysimachia: Creeping Jenny grows wild in damp woodland and its vigorous trailing stems will soon spread everywhere if not cut back after flowering. However, it is a good choice if you want to cover an area of bare soil. Lysimachia flowers are bowl-shaped and usually yellow, although both white and red forms are available. Varieiteis: The common Creeping Jenny (Moneywort) is L. nummularia, height two inches, spread two feet and the flowering period is May to August. The half-inch flowers are yellow and the round leaves are bright green. It is a dense carpeter which stifles weeds, but is far too invasive for a small rockery. Choose instead the yellow-leaved variety 'Aurea' it is much less vigorous than the species and the foliage is attractive all year round. For a ground hugging miniature grow the shade loving L. japonica 'Minutissima'. Site and Soil: Requires well-drained, humus-rich soil in sun or partial shade. Propagation: Plant cuttings in spring or divide clumps in autumn.

Mazus: is a low creeper which is closely related to Mimulus, but it is a sun lover and the flowers are in white or purple rather than red or gold. It is an easy plant to grow in a fertile spot and will tolerate light shade. It has never become popular as a rock garden plant. The flowers which appear in summer are unusual, they are two-lipped (a short one above and an extended and lobed lip below) and are attractively spotted. Varieties: The only one you are likely to find is M. reptans, height two inches, spread eighteen inches, flowering period is June to August. The slender stems hug the ground and the large purple flowers are spotted and marked with white and yellow. There is a white flowered variety ('Albus') like the species this plant is a lime-hater. M. radicans is different, the foliage is bronzy-green and the flowers white with a purple centre. It blooms in June and July flowering rather later is the dark green M. pumilio which bears yellow-centred white flowers on short stalks. Site and Soil: Requires well-drained soil, thrives in sun or light shade. Propagation: Sow seeds or divide clumps in spring.

Meconopsis has numerous species but not many are suitable for the rock garden. As a general rule the flowers are blue and the plants require acid soil. Both blooms and plants are short lived and so the stock has to be regularly replenished from seed. Best known is the Himalayan Blue Poppy a beautiful plant but too tall for the modest rockery. The odd one out is the Welsh Poppy the flowers are yellow and it is easy to grow. Varieties: The Welsh Poppy (M. cambrica) is an undemanding plant which is not fussy about soil type and produces a succession of two-inch wide clear yellow Poppies all summer long. The variety aurantiaca is orange and 'flore pleno' is semi-double. The basic details are height twelve inches, spread nine inches; flowering period is June to September. A word of warning the Welsh Poppy seeds very freely and is therefore invasive. M. quintuplinervia (Harebell Poppy) is the one to choose, lavender-blue one-inch wide Poppies which droop gracefully. Site and Soil: Requires well-drained, lime-free soil in light shade. Propagation: Sow seeds in spring.

Mimulus: Monkey Flower is a showy plant which needs moisture-retentive soil and regular watering in dry weather. Grow in a peat bed or at the side of a pond. The trumpet-shaped flowers have an open faced Snapdragon appearance, the basic colour scheme is either red blotched with yellow or a shade of yellow blotched with red, purple or brown. You can grow a variety of the popular bedding plant M. cupreus as a short-lived perennial or you can plant a rock garden species. Varieties: There are many varieties of M. cupreus from which to make your choice, 'Red Emperor', 'Whitecroft Scarlet', etc. Basic details are height nine inches, spread nine inches; flowering period is June to September. M. primuloides is a smaller plant with bright yellow flowers on short stalks. Grow M. 'Highland Red' for hardiness, and for novelty choose M. 'Andean Nymph' which bears pale cream blooms that are marked with pink (May to July). M. burnettii is copper, spotted with yellow. Site and Soil: Requires moisture-retentive soil, some shade is desirable. Propagation: Sow seeds or divide clumps in spring.

Morisia: is a low growing plant and grows wild along the coast of Sardinia and Corsica. As you would expect from its natural habitat, it requires sandy soil and full sun. Planting Morisia in heavy soil is a waste of time. When conditions are right it forms a neat and compact cushion with numerous yellow flowers arising from the tiny leaves. Do not feed Morisia; it does best in poor soil. Variety: There is a single species, M. monanthos which is sometimes listed as M. hypogaea. The basic details are height one-inch, spread six inches; flowering period is March to May. The dark and shiny leaves form a rosette and the flowers are stalkless. The early flowering habit is a welcome feature and the four-petalled cross-shaped nature of the blooms shows that it is a member of the Cabbage family. Morisia is quite a small subject and looks best when grown in a trough, or pot. Site and Soil: Requires well-drained light soil in full sun. Propagation: Plant root cuttings in late winter.

Narcissus is practical to grow in a large rock garden. The large cupped ones reach eighteen inches or more. In an average sized rock garden you should restrict yourself to the dwarfs which grow to nine inches or less. Plant bulbs as soon as you can in autumn and then leave them undisturbed for years. Do not remove the foliage after flowering until it is completely brown. Varieties: Some of the dwarf ones are Narcissus species rather than named varieties, flowering between March and April. Examples include N. bulbocodium (Hoop Petticoat), three to six inches, all-yellow with narrow petals, N. cyclamineus, six to eight inches, drooping flowers with swept back petals and N. triandrus albus (Angel's Tears), four inches, drooping creamy flowers. Named dwarf varieties include N. 'Beryl' (eight inches, creamy petals, orange cup), N. 'Jack Snipe' (eight inches, creamy petals, yellow cup) and N. Tete-a-Tete (eight inches, yellow petals and cup). Site and Soil: Requires well-drained soil in sun or light shade. Propagation: Lift overcrowded or 'blind' clumps in late summer. Divide and plant individual bulbs.

Oenothero: Evening Primrose is a large American genus with a few species which are short enough to grow in the rock garden. The silky cupped blooms are remarkably large for such low-growing plants, but these yellow or white flowers generally open in evening and close at dawn. Oenothera is not a long lived plant, but it does produce a fine display if plentifully supplied with sun, sand and an adequate amount of water in dry weather. Cut back stems in late autumn. Varieties: The largest blooms, four inches or more across are borne by the trailing O. missouriensis (Ozark Sundrops). The basic details are height six inches, spread eighteen inches and the flowering period is July to September. The yellow flowers are borne above the sprawling stems. O. acaulis is more temperamental but is considered by many experts to be a better plant. White flowers (two to three inches across) which turn pink with age appear above the Dandelion-like leaves. O. caespitosa (four inches high) has similarly coloured flowers, but the petals are notched. Site and Soil: Requires well-drained open soil and thrives in full sun. Propagation: Sow seeds in spring.

Omphalodes: flowers are borne in loose clusters above the foliage. Each one looks like a large blue or white Forget-me-not. No more generalizations can be made as the time of flowering, ease of cultivation and conditions required for success differ widely from one species to another. O. verna in woodland conditions can be vigorous enough to be invasive, but O. luciliae is so fussy that it needs to be grown in a pan in the alpine house if you want to be sure to enjoy this beauty. Varieties: O. verna (Blue-eyed Mary) is the one you are most likely to find. The flowers are blue with a white throat; an all-white variety ('Alba') is available. The basic details are height six inches, spread eighteen inches and the flowering period is February to May. The plant needs humus-rich soil and partly shady conditions, as does the more compact O. cappadocica. O. luciliae is quite different it needs a gritty, well-drained soil and plenty of sunshine. The sky-blue flowers are borne above the blue-grey foliage from May to July. Site and Soil: Depends on the species. Propagation: Sow seeds or divide clumps in spring.

Origanum: Marjoram has a shrubby growth habit and in summer pink or purple flowers appear. These small and rather insignificant flowers are partly covered by bracts. These dwarf Origanums are sun-lovers and are only moderately hardy, and need cover during the frosty weather. Varieties: The best rockery species for growing outdoors is O. amanum, height three inches, spread six inches and the flowering period is July to September. During this period-elongated pink flowers cover the ground-hugging mat of leafy stems. O. dictamnus (Amaracus dictamnus) is different; the plant is larger and forms a woolly-leaved clump. The pink flowers are borne on heads of large purplish bracts. O. vulgare 'Aureum' is grown for its yellow foliage which is especially bright in spring. Site and Soil: Requires well-drained soil in full sun. Propagation: Plant stem cuttings in late summer.