The following pages are devoted to various plants suitable for a rock garden. I have listed the requirements, height, bloom period, colour and pictures. This is to assist in choosing varieties that appeal to individual tastes. In some cases the particular colour or texture may attract some and long blooming periods are a definite asset for any garden area. Certain species are easy to grow and flourish in poor soil while others are fussy and demand specific location, winter protection and consistent watering. Hopefully this list will serve as a guide to begin your rockery, plus teach the techniques of propagation.
Acaena: New Zealand Burr is an easy to grow carpeting perennial with a number of uses, covering cracks between paving slabs, providing groundcover between plants and forming leafy blankets around dwarf bulbs. This hardy plant is low growing one to four inches tall and tolerant of poor and dry soil, but soon dies out in waterlogged ground. The dense mat of evergreen foliage spreads rapidly, so take care that choice plants are not swamped. The flowers are tiny and insignificant, but they are followed in late summer by burr-like seed heads which are often showy and colourful. Varieties: A. microphylla attains a height of approximately two inches and a spread of about two feet. The foliage is silvery when young, becoming bronze. Another red-burred variety is A. 'Blue Haze' with blue grey leaves. The most vigorous species is A. novaezealandiae; the mat of silky green foliage is very invasive. For colourful foliage choose A. buchanii or A. 'Copper Carpet' which is coppery-purple. Site and Soil: Any well drained garden soil, thrives in sun or light shade. Propagation: Divide clumps in autumn or spring.
Achillea: Alpine Yarrow can grow several feet high and are found in the herbaceous border, but there are several dwarf species which are suitable for the rockery. They form a mat of silvery or green finely divided foliage and during the summer flat heads of tiny white or yellow flowers appear. These Alpine Yarrows are useful for covering areas of dry sandy soil or crevices between rocks and the plants are easily propagated in the spring. Sprinkle Slug Pellets around the plants if leaf damage is seen. Varieties: The most popular species is A. tomentosa, basic details are height six inches, spread one foot and the flowering period is July to September. The downy greyish leaves form a dense carpet and the yellow flower heads are three inches across. Remove dead flowers to preserve evergreen habit. Varieties: Other yellow-flowering types include A. chrysocoma (A. aurea) the foliage is highly aromatic when crushed and the A. 'King Edward' has a long flowering season. For white flowers and silvery foliage pick A. argentea or A. kellereri. Site and Soil: Requires well-drained infertile soil in full sun. Propagation: Divide clumps or take cuttings in spring.
Aethionema: is a low growing shrubby evergreen which will flower for many weeks from early to late summer if the site is unshaded and the soil is free draining. All species thrive best in alkaline soil, but the popular types do well in neutral or even slightly acid soil. The grey, fleshy leaves form a dense carpet and the flower heads cover the surface. Each head is a rounded cluster of tiny flowers, varying in colour from palest pink to deepest rose depending on the variety chosen. Varieties: The popular one is A. 'Warley Rose', an excellent choice for the rock garden or for growing on an old wall. The basic details are height six inches, spread one foot, flowering period May to August and the flower colour is rosy red. A. 'Warley Ruber' is a similar plant with even more striking flowers, but is harder to find. A. grandiflorum approximately one foot is the tallest Aethionema, bearing pale pink blooms from May to August. A. pulchellum approximately nine inches is a rather similar plant but is more compact. Site and Soil: Any well-drained soil and full sun is required. Propagation: Easily raised from seed. With named varieties plant cuttings in early or late summer.
Ajuga: will thrive almost anywhere, in dry or moist soil and in sun as well as shade. Plant it as groundcover or in the crevices between rocks well away from choicer and more delicate plants. Bugle spreads rapidly and can be invasive. The flowers which appear from April to August are usually blue and appear on six-inch tall spikes. The decorative effect, however, is often derived from the foliage which forms dense mates. Multicoloured and variegated forms are available. Varieties: Most of the cultivated forms have been bred from the wild flower A. reptans. It grows about four to six inches high and leaf colour separates the different varieties, 'Burgandy Glow' (leaves green, pink and red), 'Atropurpurea' (leaves reddish-purple) and 'Multicolor' (leaves green, mottled bronze and red). 'Alba' is a white-flowered variety. A. pyramidalis is quite similar to A. reptans but usually taller. Site and Soil: Any reasonable garden soil will do, thrives in sun or partial shade. Propagation: Divide clumps in autumn or spring.
Alchemilla: Alpine Lady's Mantle is compact, forming hummocks of lobed leaves. During the summer fluffy branching sprays of tiny yellow flowers appear, but Alchemillia is grown for its foliage rather than its blooms. Its advantage is that it is very easy to grow in either rock or peat gardens, its drawback is that self-seeding can mean unwanted plants appearing anywhere. Varieites: A. alpina is a common wild flower in the Alps with a height of six inches and a spread of about one foot. The flowering period is June to August. The leaves are dark green above with silvery edges and silver below. Some of the foliage dies down in winter. Other miniature Alchemillas include A. erythropoda (similar to but less invasive than A. alpina), A. conjuncta and A. ellenbeckii (long trailing stems). Site and Soil: Any well-drained garden soil will do, thrives in sun or light shade. Propagation: Easily raised from seed sown in spring. Divide clumps in spring.
Allium: Flowering Garlic is available in many species. The tall ones are for the border and dwarfs for the rock garden. Leaves and petals may be wide or narrow, and flower heads may be loose or tightly packed. Some are sold as bulbs for planting in the autumn but many of the choice types have rhizomatous roots and are bought as growing plants. Choose with care as a few popular Alliums such as A. moly (one foot lossely packed heads of yellow stars) and A. pulchellum self seed very freely and are invasive. Varieties: A. beesianum is a tall rockery Allium with one foot stalks bearing clusters of pendant blue flowers in midsummer. Another species which bears hanging bell-like flowers in June is the pink or purple A. narcissiflorum (eight inches tall). A. ostrowskianum (six inches tall) carries its wide-petalled carmine flowers in flat clusters. For late summer blooms choose the small A. amabile (five inches tall with grassy foliage, red-purple blooms). A cyaneum (six inches tall) has small heads of upright blue flowers. Site and Soil: Any well-drained soil will do, thrives best in full sun. Propagation: Divide clumps every few years in autumn.
Alyssum: Don't reject this plant because you see it in rockeries everywhere. In spring it provides a bright yellow splash which blends well with the blues and pinks of Aubrieta. But don't let it run riot. It can soon spread and choice alpines may be swamped. When not in flower it is a greyish shrubby perennial which flourishes in poor soil. Trim back once the flowers have faded, this will keep it in check and also prolong the life of the plant. Varieties: A. saxatile (Gold Dust) is the basic species attaining a height of six to twelve inches and a spread of about eighteen inches. The flowering period is April to June. The tiny bright yellow flowers form large heads which often completely cover the foliage. There are a number of named varieties, 'Citrinum' (pale yellow), 'Dudley Neville' (buff), 'Plenum' (double yellow), 'Compactum' (neat growth habit) and the dwarf 'Tom Thumb'. Another miniature is A. montanum with a height of four inches and a spread of about twelve inches. A. spinosum (Ptilotrichum spinosum) is a spiny white or pink flowering dwarf shrub. Site and Soil: Any well-drained soil, thrives best in full sun. Propagation: Sow seeds under glass in spring. With named varieties plant cuttings in early summer.
Anacyclus: Mt. Atlas Daisy is a beauty for the rock garden. The carrot-like root produces a rosette of prostrate stems, each stem bearing grey-green ferny foliage and a Daisy-like flower at the tip. In bud only the red undersides of the petals can be seen, but when open the flower is a pure white Daisy. This plant from the Atlas Mountains of N. Africa is hardy and not difficult to grow if you meet its two basic needs, free draining, gritty soil with a covering of gravel and a sheltered site which is unshaded. Varieties: Unless you are willing to search through the specialist catalogues you will find just one species, A. depressus, sometimes listed as A. pyrethrum depressus. The basic details are height two inches, spread twelve inches and flowering period May to August. The flowers are one to two inches across. Avoid overwatering at all times and deadhead after flowering. Other species are rare and are no better than A. depressus. Site and Soil: Requires well drained open soil and full sun is essential. Propagation: Sow fresh seeds under glass in autumn or plant cuttings in a cold frame in spring.
Androsace: Rock Jasmine is a splendid alpine with approximately one hundred and fifty species. You must choose with care. Most of them are too delicate and susceptible to rain to grow outdoors, but the four species described below will succeed in the open garden. Some produce neat rosettes of foliage, others are tightly packed mounds of narrow leaves and the remainder have a trailing growth habit. All bear tiny, Primrose-like flowers. Varieties: A. sarmentosa is a popular species. It grows only four inches high but the spread of the neat foliage rosettes is up to two feet. Pink flowers appear from April to June. A. carnea is a cushion forming type, four inches high with pink flowers in spring. The easiest one is A. carnea rosea (other name halleri). A. lanuginosa is a trailer for growing over rocks. Pink flowers are produced in July and August. A. sempervivoides bears yellow-eyed flowers of delicate pink in spring. Site and Soil: A well-drained gritty soil is essential. Thrives in sun or light shade. Propagation: Use rosettes or basal shoots as cuttings, and plant in early summer.
Anemone: Windflower is a popular group for the rockery. The smaller ones with showy blooms (usually blue) appear in early spring. The three you are most likely to find are A. blanda, apennina and nemorosa. All produce rhizomes underground and the 'bulbs' of A. blanda can be bought for planting out in September. The leaves of these small Anemones are deeply cut and the flowers are either starry or Daisy-like. Varieties: A. blanda is the one you are most likely to find. Basic details are height four inches; flowering period is February to April with Daisy flowers about one and a half inches across. Named varieties include 'Atrocaerulea' (deep blue), 'Blue Star' (mid blue), 'Charmer' (rosy red) and 'White Splendour' (white). A. apennina is very similar, but the flowers are rather smaller and appear later (March to April). A. nemorosa (Wood Anemone) is taller about six to eight inches and bears glossy starry flowers in spring. The wild species is white, but blue, pink and red named varieties are available. Site and Soil: Well-drained, humus-rich soil is required, thrives in sun or light shade. Propagation: Divide mature clumps in late summer.
Antennaria: Cat's Ear is not a showy plant but does have one useful property, it can be walked on without harm. This means that it can be used as crack filler between paving stones and as the basic material for an alpine lawn. Its mat of creeping stems can also be used as groundcover around bulbs. It is tough, hardy and flourishes in poor soil. In May and June the small flower heads open with blooms in white, pink or red. Varieties: The only species you are likely to find in the catalogues is A. dioica, sometimes offered as A. tomentosa. It spreads to form a mat of silvery leaves, reaching about eighteen inches across. The tiny flowers are of the 'everlasting' type. They appear in clusters on top of erect flower stalks. The height of these stalks and the colour of the blooms depend on the variety chosen. Look for 'Aprica' (four inches, cream), 'Nyewoods Variety' (four inches, deep pink), 'Rosea' (four inches, pink), 'Rubra' (six inches, crimson) and 'Minima' (two inches, pink). Site and Soil: Any well-drained garden soil will do, thrives best in full sun. Propagation: Divide clumps in early autumn or spring.