Advice on Planting Rock Gardens
Nurserymen usually grow rock plants in smalland as they can be moved from these without disturbance they can be planted at practically any time of year. Spring is a favourable time but it is often convenient to buy rock plants in flower when one can see exactly what one is getting, and there is nothing against this provided the plants are carefully turned out of their pots and, if the weather is dry, are watered for a week or so until they are established.
Recommended Rock Plants
Acaena These are carpeting plants which are useful as ground cover and also for growing in the crevices between paving slabs since they do not mind being walked on. Their smallare followed by curious little brown or reddish heads but it is for their little that these plants are mainly grown. These are grey green in Acaena buchananii, green in A. novae zealandiae and bronzy in A. microphyla, All will grow in any reasonable soil in sun or semi-shade.
(Yarrow) In addition to the larger achilleas, which are plants for the herbaceous border or bed, there are a number of smaller kinds which are admirable little plants for the rock garden. They are mat-forming plants with flattish clusters of small , sulphur-yellow in King Edward; deep yellow in A. tomentosa; white, with silvery leaves in A. argentea. They mostly flower in late spring and early summer but King Edward is rarely without some flowers all the summer.
All are easily grown in sunny places and well-drained soils and are increased by division in spring or autumn.
Aethionema (Stone cress) These are really tiny shrubs, but far too small for the shrub garden, and their proper place is the rock garden or dry wall. In time they will make foot-wide mounds of slender 9-in (23-cm)closely set with narrow leaves and surmounted in spring by clusters of small pink flowers. One of the finest is Warley , as it is neater and more compact in habit than most and has brighter pink flowers.
This variety must be raised fromin a frame in mid-summer but the wild species, such as Aethionema grandiflorum and A. pulchellum, can be raised from sown in spring. All like light, well-drained soils and sunny places.
Alyssum (Gold dust) The sweet alyssum, Alysswn maritimum, with white honey-scented flowers all summer, is anand though it can be grown in the rock garden it can seed itself about so freely as to become a nuisance. The kind most commonly grown in rock gardens and on walls is yellow
alyssum or gold dust. A. saxaiile, a vigorous tufted plant 9in (23cm) high with fine clusters of small yellow flowers in spring. In addition to the common form, with deep golden-yellow flowers, there is an even better variety, named /lore pleno, with double flowers, and a lemon-yellow, single-flowered variety named citrinum.
The double-flowered kind must be raised fromin a frame in spring but the single-flowered kinds can be readily raised from seed, though there may be some variation in the flower colour of the . Often the plants seed themselves about freely. All like sunny places and well-drained soils.
American cowslip, see Dodecatheon
Androsace Delightful mountain plants, some cushion forming, some trailing, but all with neat little heads of rounded pink or white flowers like pieces of confetti. They like sun and sharpand .are completely happy sprawling over the face of a terrace wall or a small boulder in the rock garden. Two of the best are Androsace lanuginosa, a trailing plant, and A. sarinen-tosa, which increases its soft hummocks of growth by pushing out short runners in all directions. Both carry their pink flowers on 5-in (13-cm) stems in late spring or early summer. They can be increased by division in spring.
(Windflower) The Japanese is loo big for the rock garden and the brilliantly coloured varieties of coronaria, the poppy so popular as a cut flower in early spring, may be considered a little loo sophisticated, though they are sometimes planted. But there is nothing wrong with either A. apennina or A. blanda as rock garden plants, for both make low clumps of deeply divided leaves smothered in early spring by fragile blue. Pink or white flowers. They are grown from little tubers which can be purchased in early autumn and planted 2 in (5 cm) deep in soil containing plenty of peat or leafmould and. For preference, a sunny place, though they will grow in partial shade. They are increased by separating out the clusters of tubers in summer. For the plant often known as A. Pulsatilla, see Pulsatilla.
Aquilcgia (Columbine) Most of the colum-bines are for the herbaceous border or wild garden, but a few are sufficiently small for the rock garden. One of the best of these isglandulosa, 9 in (23 cm) high with light blue and white flowers of the typical columbine shape in early summer.
It likes a sunny place and a well-drained but cool soil containing plenty of grit and peat or lcafmould. It can be increased by seed in spring.
Arabis One of the most popular of all white-flowered trailing plants is Arabis albida. It flowers in spring and makes a first-rate companion for the blue and pink aubrieta on walls, rock gardens and banks. There is a double-flowered form which is even more effective than the more common single, and also a pink variety named rosea or Rosabella.
All like sunny places and will grow in almost any soil. The singles can be raised from seed sown in spring but the double-flowered variety must be increased by cuttings in a frame in late spring or early summer.
Arenaria No plant makes a closer carpet of shiny bright green leaves than Arenaria balearica. It makes excellent ground cover for small bulbs and is also very attractive when covered in spring in its own white flowers. Arenaria caespitosa makes low, moss-like mounds and is particularly useful in its golden-leaved variety aurea. Quite different in character is A. montana, a trailing plant with quite large white flowers rather like those of the native stitchwort. A. balearica grows best in rather moist soil but the others grow well in ordinary soil and an open. All can be increased by division in spring or autumn.
Armeria (Thrift) Tufted plants with narrow, grass-like leaves and almost globular heads of small pink or red flowers in late spring and early summer. The best kind for the rock garden is Armeria maritima which itself has pale pink flowers but has produced garden varieties with deeper carmine flowers and also a white-flowered form.
All are accustomed to growing in very stony places in full sun and this is what they like, though they will grow almost anywhere. They can be increased by division in the spring.
Most of the perennial asters are far too big for the rock garden but there are a few exceptions, notably Aster alpinus, (23 cm) high with mauve daisy-like flowers in late spring and early summer; A. sub-eaeruleus, 1 ft (30cm) high with bright blue flowers at the same period, and A. yun-nanensis, 18 in (45cm) high, with deep blue flowers around mid-summer.
All will grow in any sunny place and reasonably well-drained soil and can be increased by division in spring.
Aubrieta (Rock cress) One of the most
popular of spring-flowering, trailing plants for rock garden or dry walls and an essential companion for white-flowered arabis and yellow alyssum. The aubrieta is typically a blue-flowered plant but there are also pink-, purple- and crimson-flowered varieties. Plants can easily be raised from seed sown in spring butvary in colour for ‘which reason selected garden
varieties are increased by cuttings of young shoots in a frame about mid-summer.
Aubrietas like sunny places and will grow in practically any soil, though they particularly like soils containing lime or chalk.
Bellllower, see Campanula
Bellis (Daisy) Bellis perennis is the common daisy of lawns, not to be admitted to the garden in its wild form, but it has produced double-flowered varieties, some with much larger flowers, these being used for spring bedding displays, and one, named Dresden China, with tiny double pink flowers which look exquisite in the rock garden. Oddly enough it is not a particularly easy plant to grow, needing good, a sunny place and freedom from the competition of more vigorous plants which can easily overrun it. Increase is by division at almost any time.
Broom, see Cytisus and
Campanula (Bellflower) There are tall cam-panulas for the border and small, tufted or trailing campanulas for the rock garden. One of the best of these is Campanula portenschlagiana (syn. C. muralis) with in-numerable deep blue bell-shaped flowers from mid- to late summer. At this season it is one of the best plants for the rock garden. C. poscharskyana spreads even more rapidly. Has pale, more widely open flowers and starts to flower earlier. C. cochlearifolia (syn. C. pusilla) hangs its little blue or white flowers on slender 4-in (10-cm) stems in early summer, and C. garganica makes a carpet of growth studded with starry light blue flowers in summer. C. carpatica is larger than any of the foregoing, with quite big cup-shaped flowers held erect on 9-in (23-cm) stems in mid-summer. There are light blue, dark blue and white-flowered varieties. Catalogues contain the names of a great many more campanulas, many of them raised in gardens.
Most are easily grown in full sun or partial shade and any reasonably porous soil. They are increased by division in spring or autumn.
Candytuft, see Iberis
Catchfly, see Silene
Cerastium (Snow in summer) These grey-leaved plants with abundant white flowers in early summer spread so rapidly that they can be a menace in the rock garden, taking complete charge and smothering all less vigorous plants. Yet for covering rough places quickly they have a use. And they will grow in the poorest soils and driest places. The kind most commonly grown is Ceras-tium tomentosum, but C. biebersteinii is equally effective and a little less invasive. Both can be increased by division at practically any time.
Cheiranthus (Wallflower) Most of the wall-flowers are used for bold displays of colour in spring bedding schemes and are too big and too impermanent for the rock garden. But there are one or two exceptions includeing Cheiranthus Harpur Crewe, a bushy little plant, 1 ft (30 cm) high, with double yellow flowers in spring. It likes sandy, well-drained soils and sunny places, and can be increased by cuttings in spring or summer.
Chiastophyllum Chiastophyllum oppositifo-lium, often known as Cotyledon simplici-folia, is a good plant for a sunny crevice or shelf in the rock garden. It makes a rosette of fleshy leaves from which arise in late summer little arching stems laden with bright yellow flowers, the whole no more than 6in (15cm) high. It is increased by division in the spring.
Columbine, see Aquilegia
Convolvulus There is only one kind of con-volvulus that properly belongs in the rock garden and this is a bushy little plant about 1 ft (30cm) high with silvery leaves and white flowers in summer, named Convolvulus cneorum. It needs a rather sheltered, sunny place as it is none too hardy. It likes well-drained soil and is increased by cuttings in summer.
Corydalis (Fumitory) Corydalis lutea is a pretty little foot-high plant with elegant fern-like foliage and sprays of yellow flowers in summer. In gardens it usually spreads itself by seed and can become rather a nuisance but is a useful plant for clothing walls and rocky, difficult places. It will grow’ in sun or partial shade and seems able to survive with a minimum of soil. More garden worthy are C. cheilanthifolia, with showy yellow flowers, and C. cashmeriana with peacock-blue flowers. The last named needs a lime-free, rather peaty soil and protection from strong sunshine.
Cotula Carpeting plants which, like acaena. Have the merit of being completely prostrate and able to withstand quite a lot of wear so that they are suitable for planting in the crevices between paving slabs. The kind commonly planted is Cotula squalkla. With small, divided green leaves. It will grow in any soil in sun or semi-shade and can be increased by division at almost any time.
Cotyledon, see Chiastophyllum
Cranesbill, see Geranium
In addition to the large-flowered cyclamen, which are popular pot plants for the and are sold in great numbers in florists” shops around Christmas, there are some which are quite hardy and suitable for the rock garden, wild garden or woodland. One of the best and easiest to grow is Cyclamen neapolitanum, (syn. C. hederaefolium) with dark gr.een leaves hand-somely marbled with white, and small pink flowers on 4-in (10-cm) stems in early autumn. C. count is still smaller and produces its deep crimson flowers in late winter or early spring, and C. europaeum its rather lighter red flowers in late summer.
All produce corms, like the greenhouse cyclamen, and these are sometimes sold dry. It is not the best way to start, however, as sometimes these dry corms fail to grow. The corms are best started into growth in seed boxes filled with damp peat and placed in a greenhouse or frame, the young plants not being planted out until the spring. A better
way to start is to purchase growing plants in (or tapped out of) pots. Once established in the garden in a partially shaded place they often spread freely by self-sown seed if well supplied with peat or lcafmould. They should be left undisturbed as long as possible.
Cytisus (Broom) Most of the brooms are big shrubs but one or two are sufficiently small to be grown in the rock garden. Cytisus beanii makes a little bush about 1 ft (30cm) high smothered in yellow flowers in spring. C. kewensis produces showers of arching stems, the whole no more than 15 in (38cm) high but possibly spreading over two square yards of ground, with pale yellow flowers in spring. C. purpureas creeps about by underground stems but remains low to the ground and bears rather dull purplish flowers in late spring. All like sunny places and are not fussy about soil.
Daisy, see Bellis
Many daphnes are too big for the rock garden but Daphne hlagayana is a prostrate shrub which likes to grow with stones holding its sprawling stems to the soil. The creamy-white flowers come in spring and are intensely fragrant. So are the pink flower clusters of D. cneorum, a little shrublet 12 in (30cm) high, flowering in spring.
Both like a sunny place and well-drained soil and can. Be increased bythe stems in late spring, or D. cneorum by summer cuttings.
(Pink) A great many of the smaller kinds and varieties of dianthus make excellent rock plants. Three of the best are the maiden pink, deltoides. A trailing plant with masses of rosy-red flowers from mid-summer onwards for several weeks; the Cheddar pink. D. caesius, or gratiano-politanus, a tufted plant with soft pink flowers in late spring, and D. neglectus, which makes close cushions of narrow leaves on which sit. In early summer, the almost stemless rose flowers with bull’ reverse.
All these, and the many other kinds offered in the catalogues of rock garden specialists, thrive in sunny places and gritty well-drained soils. Most do well on limestone or chalk. The species can be raised from seed but specially selected garden varieties are increased by cuttings in early summer or by careful division in spring.
Dodecatheon (American cowslip, shooting star) Pretty plants for damp but open places, particularly around pools or at the side of streams in the rock garden. Despite the popular name they have little resemblance to cowslips, the rosy-purple or white petals of the flowers being turned back like those of a cyclamen. They are, however, carried on bare 12-in (30-cm) stems rather in the manner of a cowslip and they appear in late spring. The best method of increase is by seed sown in a greenhouse or frame in spring. Dodecatheon meadia is the easiest.
Edelweiss, see Leoniopodium
Erinus A little rosette-forming plant which will establish itself in a wall and other stony places with little or no soil and produce short spikes of purple flowers in spring. The kind cultivated is Erinus alpinus which has a white variety, albus, and a carmine variety, Dr Hanelc. This last must be increased by division but the others can be raised from seed and usually spread naturally by self-sown seedlings.
Erodium (Heron’s bill) Pretty little plants most of which either make small hummocks or spreading carpets of growth. Erodium corsicum has grey leaves and rose-pink flowers throughout the summer. E. reichar-dii rosewn makes a mat of soft green leaves studded with pink flowers from late spring to autumn.
These and other kinds can be grown in any reasonably well-drained soil and open position and they are readily increased by division in spring or autumn.
Erysimum Bushy plants closely allied and similar in appearance to wallflowers. The best are Erysimum alpinum Moonlight with pale yellow flowers, and E. linifolium, bright purple, both flowering in spring and early summer.
They like sunny places and well-drained soils and grow well on chalk or limestone.
Increase by cuttings in spring or summer, or E. linifolium by seed in spring.
Evening primrose, see Oenothera
Flax, see Linum
Fumitory, see Corydalis
Genista (Broom) Most of the genistas are too large for the rock garden but a few, such as Genista lydia and G. tinctoria Jlore-pleno are useful rock garden shrubs. The first makes a low, wide-spreading bush of arching branches covered in bright yellow flowers in early summer. G. tinctoria flore-pleno is practically prostrate and will spread for several feet, smothering itself with double yellow flowers in early summer.
These and other kinds of genista like well-drained soils and sunny places and can be increased by cuttings in summer, and G. tinctoria also by careful division in autumn or early spring.
Gentian, see Gentiana
Gentiana (Gentian) Almost all the gentians that matter from the garden standpoint are low-growing, spreading plants. The one notable exception is the willow-leaved gentian, Gentiana asclepiadea, which makes slender arching stems 18 in (45cm) or so in height, bearing purple or white blooms in summer. It is a plant for cool, partially shady places.
Most of the other kinds like sunny, open places in soil containing plenty of peat or leafmould as well as gritty sand to keep it open.
Gentiana acaulis is typical of the family, making spreading tufts of growth on which the large, deep blue flowers sit in spring. It is one of the few kinds that does well on chalky soil. G. verna is much smaller, even brighter in colour, and more difficult to grow. It dislikes lime in any form. There are several summer-flowering kinds with clusters of purple flowers and for early autumn there is the lovely Chinese gentian, G. sino-ornata, with deep sky-blue flowers. It also dislikes lime and will grow in practically pure peal and sand. G. macaulayi, a vigorous hybrid between G. sino-ornata and G. farreri, has a white throat and needs the same treatment.
Easier to manage are the summer-flowering gentians such as G. freyniana, G. lagodechiana and its variety septemjida. These are semi-trailing plants with clusters of deep blue flowers and they will grow in the ordinary rock garden soil mixture without difficulty.
All these gentians can be increased by careful division in spring and most can also be raised from seed sown in a greenhouse or frame in spring.
Geranium (Cranesbill) In addition to the popular bedding geraniums, which are really pelargoniums, and the quite large hardy geraniums for the herbaceous border or bed, there are several much smaller kinds that can be grown in the rock garden. One of the best is Geranium subcau/escens, a trailing plant with 6-in (15-cm) stems. Carrying, in early summer, remarkably bright rose-purple flowers. G. sunguineum makes mats of growth, studded in spring and summer with magenta flowers, but it is apt to be invasive. A better plant is a less vigorous variety of it named lancastriense. With clear pink flowers.
All are readily grown in any reasonable soil and open position, and can be increased by division in spring or autumn.
Most of the geums are for the herba-ceous border rather than for the rock garden, but the foot-high borisii, with orange-red flowers from late spring to autumn, is suitable for both, and the prostrate yellow-flowered G. reptans is definitely a rock plant. It flowers in early summer and likes a sunny place and very gritty, sharply drained soil. G. borisii will grow in any reasonably well-drained soil. Both can be increased by division in spring.
Gold dust, see Alyssum
Gromwell, see Lithospermum
Gypsophila These are also primarily border plants but Gypsophila repens is a slender. Trailing plant with grey-green leaves and showers ofsmall white flowers in late spring and early summer. It has an even prettier pink variety named rosea. This is a plant for sunny crevices and shelves in the rock garden or on the face of a wall. It will grow in any reasonably well-drained soil, but particularly likes chalk and limestone. It can be increased by seed sown in spring.
Helianthemum (Rock rose, sun rose) Bushy. Sprawling plants admirable for planting on sunny rock gardens or dry walls. The flowers do not last long but are constantly replaced, so that a plant will remain highly decorative for many weeks in late spring and early summer. The colour range is from white and pale yellow to orange, copper and crimson. Most varieties have single flowers, but a few, such as Jubilee, yellow, and Fireball. Crimson, are double. Habit is improved by trimming the young growth with shears or secateurs after flowering, but do not cut back into the hard old wood.
All can be increased by cuttings in summer in a propagating frame and seed may also be sown in spring, but seedlings are likely to vary greatly in colour and quality of flower. It is better to increase from cuttings to obtain uniform plants.
Heron’s bill, see Erodium
Houseleek, see Sempervivum
(St John’s wort) Shrubby or trailing plants, some of which make excellent rock plants. The best for this purpose are olympicum, I ft (30cm) high with pale yellow flowers; H. repens, with thin, wiry stems and deep yellow flowers; H. coris, which in appearance is intermediate between the last two, and H. fragile, 6 in (15 cm) high, with pale gold flowers.
All thrive in any ordinary soil and open, sunny position, and can be increased by seed sown in spring, or some kinds by careful division, also in spring.
Iberis (Candytuft) There are both annual and perennial candytufts and it is the latter that are good rock plants. They are equally suitable for a sunny rock garden or dry wall. They grow about 9in (23 cm) high, have evergreen foliage, and white flowers in late spring.
One of the best varieties is Iberis semper-virens Snowflakc. The lowest growing kind is /. saxatilis, which often does not exceed 3 in (8 cm) in height, though it can spread quite a lot. /. gibraltarica is taller and has-pink flowers but is less hardy and reliable than the others.
All can be grown from seed, though seedlings are unlikely to flower before their second year and may vary a little in quality. Alternatively, cuttings can be rooted in a frame in summer and will exactly reproduce the qualities of the parent plant.
Kenilworth ivy, see Linaria
Leontopodium (Edelweiss) Leontopodium alpinum is a rock plant with narrow grey leaves, and tiny flowers surrounded by star-shaped clusters of bracts which are densely clad in white down. It is grown more for sentiment and because of the many legends attached to it than for its beauty, though it is not unattractive in a quiet way. It should be given an open, sunny place in well-drained soil and will benefit from the protection of a pane of glass in winter, supported a few inches above it, to ward oil rain. Propagation is by division in spring.
Lewisia Very attractive plants bearing line sprays of flowers above fiattish rosettes of leaves. Some kinds are rather dillicult to grow, but there is a race of garden hybrids which will grow well in sunny places and gritty, well-drained but not dry soils. They are ideal plants for the crevices in a dry wall with an ample body of soil behind it. The fine flowers of these hybrids are in shades of peach, apricot, salmon and pink, and are borne on 9- to 12-in (23- to 30-cm) stems in late spring and early summer.
As a rule the plants are not very long lived, but they can be renewed fairly easily from seed sown in a frame or greenhouse in spring.
Linaria (Toadflax. Kenilworth ivy) Two very different kinds of toadflax may be grown in rocky places. One, a true mountain plant, is Linaria alpina, which might be likened to a tiny antirrhinum, with slender 4-in (10-cm) spikes of purple or shrimp-pink flowers in summer. It likes sunny places and gritty soils, and is raised from seed sown in a frame or greenhouse in spring.
The other, Linaria aequitriloba, has been renamed Cymbalaria aequitriloba and may be found so listed in some catalogues. It is a carpeter with little lavender flowers sitting on the close carpet of rounded leaves. It is an excellent plant to grow in the crevices between paving slabs and it will thrive in sun or shade in any reasonable soil. Increase is by division at almost any time.
Linum (Flax) Linum perenne is a slender. Elegant plant with pale blue flowers produced in summer in loose sprays on 18-in (45-cm) stems. L. narbonnense is very like it, but a shade deeper in colour. L. flavum is about 9 in (23 cm) in height and it has more compact clusters of bright yellow flowers. And the so-called tree flax. L. arborewn, is a tiny bushling of 9 to I2in (23 to 30cm). otherwise very much like the last. Gem-mell’s Hybrid, probably a hybrid between these last two species, is a particularly good form of yellow-flowered flax and probably the best for general planting.
All these flaxes like sunny places and well-drained soils. They can be raised from seed sown in a frame or greenhouse in spring, or L. arborewn by cuttings in a frame in summer: a method which is essential for Gemmell’s Hybrid as it is variable in colour and flower quality if raised from seed.
Lithospermum (Gromwell) One of the loveliest of pure blue flowers for the sunny rock garden, rock bank or dry wall is Lithospermum diffusion, also known as L. prostration, a trailing plant with flowers individually quite small, but so blue and produced so freely in late spring and early summer that there are few plants to equal it for beauty at this season. The two finest varieties are Heavenly Blue and Grace Ward.
All need a lime-free and well-drained soil, but otherwise are not in the least difficult to grow. Increase is by cuttings in a frame in summer.
Mentha This is the botanical name for mint. Few kinds of which should be allowed any-where near a rock garden, but one kind, the Corsican mint, Mentha requtenii, is a useful carpeter for cool, rather moist places. It can be used over small bulbs or in the crevices between paving slabs where it will emit its strong minty aroma when walked on. It is increased by division in spring.
Moss pink, see Phlox
Oenothera (Evening primrose) Some kinds of evening primrose are far too large and coarse for the rock garden, but there are exceptions. Oenothera missouriensis is a trailing plant with large, pale yellow flowers in late summer and autumn which will grow in any reasonable soil and sunny place and is quite at home in a rock bed or rock garden. Divide orseed in spring.
Omphalodes Omphalodes vema is rather too rampant for most rock gardens, but two other kinds with a much neater habit are worth growing in this part of the garden. O. cappadocica has blue-grey leaves and sprays of small blue forget-me-not llowers in spring and is not fussy about soil. It will grow well in sun or semi-shade. O. luciliae is more tufted in habit with blue-grey leaves and azure-blue flowers on 6-in (15-cm) stems in late spring. It enjoys sun and well-drained but not dry soil; slugs are very fond of it. Both kinds can be increased by division in spring.
Onosma These are very distinctive plants to grow in the crevices of a dry wall, or in a sunny rock garden with perfect drainage. They grow especially well on chalk and limestone. Onosma tauricum carries golden-yellow flowers above its tufts of downy, grey-green leaves. The flowers are tubular and carried in curling spikes in early summer. One of the easiest to grow, it has the common name of golden drops. O. alboro-sewn with white flowers that change to pink as they age is more resentful of excess moisture, especially in autumn and winter. Both kinds can be increased by seed in spring.
Oxalis Sun-loving plants for the rock garden or, in the case of Oxalisfloribunda (it is often called O. rosea), as an edging to beds. The two best rock garden kinds are 0. enneaphylla and O. adenophylla, rather similar plants with clustered flowers in summer, white in the first, pink-flushed in the second, sitting close down on the tufted blue-grey leaves.
They need the best possible drainage and rather light, gritty soil and plenty of-mould or peat to retain moisture in summer without becoming too waterlogged in winter. O. adenophylla likes full sunlight while O. enneaphylla prefers a light place which will not be scorched by too much direct sunshine.
By contrast O.jloribunda will grow in any warm, sunny place and does not mind how poor the soil is. Its bright rose flowers in loose sprays are produced all the summer. It can be easily increased by division in spring, and O. enneaphylla can also be carefully divided, but O. adenophylla can be increased only by seed.
Papaver (Poppy) The only poppy for the rock garden is a mountain kind named Papaver alpinum, a charming little plant like a miniature Iceland poppy, with fragrant white, yellow or orange flowers on 4-in (10-cm) stems in summer. It seldom survives for long, but since it reproduces itself from seed in well-drained, gritty soil, it is not difficult to maintain a succession of plants. It must have a sunny place.
Pasque flower, see Pulsatilla
Penstcmon There are several small penste-mons worth growing in the rock garden. Notably Penstemon heterophyllus, a plant with sturdy 15-in (38-cm) spikes of blue flowers all summer; P. scolderi. A more compact plant with-blue flowers on 9-in (23-cm) stems in late spring and early summer; P. rupicola, almost prostrate and with ruby-red flowers.
All like well-drained soils and sunny rather sheltered places, and can be increased by cuttings in summer or seed in spring.
Phlox (Moss pink) The moss pink Phlox subulata, is a mat-forming plant with narrow leaves and mauve, pink, rose or white flowers in late spring. There are numerous garden varieties and all arein reasonably open places and almost any soil. P. douglasii is more compact in habit and needs well-drained. Rather gritty soil. It has numerous excellent varieties. P. divaricate is a taller plant with 9-in (23-cm) stems bearing loose clusters of mauve or lavender flowers, which are a good clear blue in the variety laphamii, in spring and early summer.
Varieties of P. subulata and P. douglasii are best increased by cuttings in summer. P. d. laphamii by division in spring. The species also grow from seed but seedlings may vary in flower colour.
Pink, see Dianlhus
Polygonum (Knotweed) There are vigorous climbing polygonums and herbaceous kinds that do not seem to know where to stop, but there are also a couple of small mat-forming kinds that are excellent for the rock garden or wall. One of these is Polygonum vaccinii-folium, with little slender spikes of pink flowers and the other, P. affine, with rather stouter spikes of rose or carmine flowers. Both flower in late summer and early autumn, like sunny places and are not at all fussy about soil. They can be increased by division in the spring.
Poppy, see Papaver
Potentilla There are several small potentillas suitable for the rock garden. One of the best is Potentilla tongue I, a creeping plant with orange-bull” flowers from mid-summer to autumn. P. alba makes a wide-spreading carpet of leaves studded with white flowers all summer. Both P. aurea and P. verna nana have bright yellow flowers, most effective in a double-flowered variety of P. aurea named flore plena.
All these will grow in any reasonably well-drained soil and open position and can be increased by division in the spring.
Primula (Primrose) In addition to the wild British primrose, which has produced various coloured and double-flowered varieties of garden merit, and the polyanthus. Which is a cluster-flowered form of primrose. There are a number of other hardy primroses which are excellent plants for the rock garden, the side of a pool or woodland. Primula juliae is a mat-forming plant with almost stemlcss deep carmine flowers. It has given a whole race of hybrids with the British primrose, all pink or magenta in colour and often collectively known as P. Juliana. Wanda, crimson magenta, is one of the best known and a first-class plant.
The drumstick primrose. P. denticulata. Has mauve, pink or white flowers in an almost spherical head on 5-in (13-cm) stems in spring, and will grow anywhere, though it has a preference for rather damp spots. So has P. rosea, a brilliant little spring flower for the waterside with intense deep rose flowers on 3-in (8-cm) stems.
The candelabra primroses, which include P. japonica, P. pulverulenta and P. helodoxa, are also plants for damp places. They will thrive along the sides of drainage ditches in leafy or peaty soils and are also at home in the woodland. Their pink, magenta or. In P. helodoxa. Yellow flowers, are produced in candelabra-like sprays 2 ft (60cm) high.
The Tibetan cowslip, P. Jlorindae. Will actually grow in shallow water, though it is better in the bog garden where it is damp but not actually covered with water. The same is true of the Sikkim cowslip, P. site-kimensis. Both have big heads of nodding yellow flowers like giant cowslips.
For drier places, such as ledges or crevices in the rock garden, there is P. marginata, with heads of lavender-blue flowers, P. edgeworihii, also lavender-flowered, both out in early spring, and the numerous varieties of P. auricula which are much easier to manage and can be grown as edgings to flower borders if there is no room for them in the rock garden.
All these hardy primroses can be increased by careful division in spring, also by seed sown as soon as ripe or also in spring. Many kinds will spread themselves by self-sown seed.
Pulsatilla (Pasque flower) The beautiful Pulsatilla vulgaris was for long known as Anemone Pulsatilla, and may still be found so listed in some nursery catalogues. It makes a low clump of softly hairy leaves from which, in spring, grow 9-in (23-cm) stems bearing large mauve-purple flowers followed by tangled, silken seed heads. There is considerable variation in colour from pale reddish forms to blue purple, but all are beautiful.
This is a plant that grows naturally on chalk downs. It likes open, sunny places and well-drained soils, and it can be increased by seed, but because of the colour variation specially selected forms are increased by careful division of thein spring after flowering.
Ramonda Very distinctive plants for shady places in soil containing plenty of peat or leafmould. They make flat rosettes of leathery leaves from the centres of which the 6-in (15-cm) flower stems are produced in late spring. The most popular kind is Ramonda myconi with bluish-lilac flowers. R. nathaliae is nearer to blue and there are also white and pinkish forms.
All like to grow on their sides in vertical crevices so that water does not collect in their rosettes; they do well facing north. Increase is by seed in spring orin early summer.
Raoulia One of the most beautiful carpeting plants but not one of the easiest to grow. Raoulia australis makes a completely flat mat of shiny silver leaves and can be used over choice rock garden bulbs, but it does require a gritty, well-drained yet not dry soil. It is increased by division in the spring.
Rhodohypoxis Another little beauty that is notwell, Rhodohypoxis baurii makes tiny tufts of narrow leaves and bears its white, pink or carmine flowers like brightly coloured moths, on 3-in (8-cm) stems in summer. It- needs peaty, lime-free soil with plenty of moisture while it is growing in late spring and summer but no excess of water in winter. It should only be moved in spring and can be divided then or grown from seed sown in moist peat and sand.
Rock cress, see Aubrieta
Rock rose, see Helianthemum
St John’s wort, see Hypericum
Saponaria (Soapwort) The most popular kind is Saponaria ocymoides, a spreading plant for sunny banks, rock gardens or walls. It grows rapidly and around midsummer covers its loose mounds of growth with bright pink flowers.
It likes sunny places, will grow in almost any soil and is readily increased by division in spring or autumn.
Saxifraga (Saxifrage) There are a great many different kinds of saxifrage and they vary so much in appearance that it is not immediately obvious that all are related. From the garden standpoint fourare most valuable – the silver saxifrages, the cushion saxifrages, the mossy saxifrages, and the London prides.
The first two are plants for sunny crevices and ledges in the rock garden or dry wall. The silver saxifrages make flattish rosettes of leaves, often silvered all over or along the edges, and they produce clusters or sprays of flowers, usually white, though there are pink and even yellow varieties. One of the loveliest is Tumbling Waters with arching 2-ft (60-cm) flower sprays in early summer.
The cushion saxifrages make low hum-mocks of usually greyish leaves which often have a hard and spiky feel. The flowers. Which may be white, pink or pale yellow, are produced in early spring on 1- to 3-in (25- to 8-cm) stems. Typical of this lovely group is Cranbourne, with flowers the colour of apple blossom; Saxifraga burseriana, pure white, and S. elizabethae, yellow, but there are many more.
Both the silver and the cushion saxifrages thrive in well-drained, gritty soils, preferably containing plenty of limestone clippings, and they like open places.
By contrast, the mossy saxifrages thrive in ordinary soils and do not object to shade. They make soft, low mounds of much divided green leaves and carry sprays of white, pink or red flowers on 6- to 9-in (15- to 23-cm) stems in spring. They can be grown in the rock garden, but are equally good for edging a bed or border. Typical kinds are James Bremner, white; Winston Churchill, pink, and sanguined superba, crimson.
The London prides are best known by the common London pride Saxifraga um-brosa, a plant with rosettes of green leaves and loose I-ft (30-cm) sprays of small pink flowers in early summer. It will grow anywhere in sun or shade. It is splendid on walls, in shady borders and in big rock gardens, but in small rock gardens a better plant is the small London pride, S. it. Primuloides, which is at its most beautiful in Ingwersen’s Variety. This is only 6in (15 cm) high and has deep pink flowers in late spring.
Almost all saxifrages can be increased by division in spring and most can also be raised from seed sown in a frame or greenhouse in spring, though it may be a year or two before seedlings attain flowering size, and they may vary in flower colour from their parents.
Saxifrage, see Saxifraga
(Stonecrop) Succulent plants, many of which are quite hardy and can be grown on sunny rock gardens, dry walls, banks. Etc. Most will grow in quite poor and dry soils. Some, such as Sedwn spatliulifolium, with yellow flowers, and S. spurium, with pale pink flowers in summer, are quite prostrate plants which can cover a considerable area in time. Others are more tufted. One of the smallest in leaf is S. hispanicum, a creeping plant with blue-grey leaves so small that the plant almost looks like a moss. This and similar small kinds such as S. lydium, with reddish bronze leaves, and S. dasyphyllum, with blue-grey leaves, can be planted in the crevices between paving slabs.
Most stonecrops can be increased by division in spring or autumn, but a few, including 5. caeruleum with small pale blue flowers, aregrown from seed sown in spring.
Sempervivum (Houseleek) The semper-vivums do flower but they are grown primarily for the decorative merit of their rosettes of succulent leaves which are variously coloured and sometimes covered with a cobweb-like network of hairs. One of the best of these cobweb houseleeks is Sempervivum arachnoideum. It has small rosettes not much over 1 in (1 cm) in diameter in contrast to the 3-in (8-cm) rosettes of the common houseleck, S. tectorum.
Many more varieties will be found in catalogues and all will grow well in hot, dry places with a minimum of soil once established, though some good loam, alkaline rather than acid, plus a dash of bone-meal and some limestone chippings will get them started. Divide in spring.
Shooting star, see Dodecatheon
Silene (Catchfly) Three silenes are useful rock garden plants. The smallest is Silene acaulis which makes tight cushions of growth studded with pink flowers in spring; S. alpestris makes carpets of small shining leaves and carries its white flowers on slender 6-in (15-cm) stems in late spring and early summer, and S. schafta, a taller, looser plant, is the last to bloom in late summer and early autumn, when it is covered with rose-carmine flowers.
All like sunny places and well-drained soils and can be increased by division in spring.
Sisyrinchium Not all kinds are easy to grow and one of the most beautiful, Sisyrinchium grandifiorum, with rush-like leaves and bell-shaped amethyst-purple flowers on slender 9-in (23-cm) stems in early spring, needs a moist yet porous mixture of peat, sand and stone chippings to make it really happy. But S. august (folium, the blue-eyed grass, so called because of its narrow leaves and starry blue flowers, will grow in any reasonably good soil and sunny place where it will often become naturalized and seed itself about freely. It is 9in (23 cm) high. Flowers in early summer and can be increased by seed or division in spring.
Snow in summer, see Cerastium
Soapwort, see Saponaria
Soldanella Very beautiful little plants with small rounded leaves and nodding stems with fringed violet flowers. The two most popular kinds are Soldanella alpina, 3 in (8 cm) high and S. montana, 3 to 4in (8 to 10cm) high. Both need a very porous but not dry mixture of soil, peat and sand or stone chippings and a sunny place. They are not easy plants and are often grown in pans in a frame or unheated greenhouse to protect them against winter wet which can cause them to rot off.
Stone cress, see Aethionema
Sun rose, see Helianthemum
Thrift, see Armeria
, see Thymus
Thymus (Thyme) Small perennials with aromatic foliage, suitable for the rock garden, wall and paving. They are either completely prostrate, as in pink-, carmine-or white-flowered Thymus serpyllum, or make neat little bushes, as in T. carnosus (often listed as 7*. nitidus) and T. cilriodurus, the lemon thyme, so called because of its distinctive aroma; both have pink flowers.
All like sunny places and well-drained soils and flower in late spring and early summer. The creeping kinds can be divided in spring, the shrubby kinds increased by cuttings in summer.
Toadflax, see Linaria
Most of the veronicas are shrubs or herbaceous plants, far loo big for the rock garden, but a few are small creeping or tufted plants. One of the best is prostrata, a mat-forming plant with little 3-in (8-cm) spikes of bright blue flowers in early summer. V. catarractae makes a tiny bush, 1 ft (30cm) high, with off-white flowers all summer. Both like sunny places but will grow in any reasonable soil. V. rupestris is easily increased by division. V. catarractae from seed or cuttings.
All violas can be grown in the rock garden, but it is the small-flowered varieties. Such as Viola gracilis, V. cornuta and their varieties, that look most at home there. These are sprawling plants bearing a constant succession of flowers in late spring and early summer. Typical V. gracilis has deep violet-purple flowers, typical V. cornuta. Light blue, but there are numerous garden varieties of each as well as hybrids. Ranging in colour from white, cream and lavender to deep yellow and purple.
All like cool, partially shaded places and soils with plenty of leafmould or peat. They can be increased by division in spring or by cuttings in summer.
Wallflower, see Cheiranthus
Windtlower. See Anemone
Yarrow, see Achillea