Planting and Cultivating Rock Plants
Rock plants are almost invariably sold in pots or other small containers from which they can be planted at any time of the year whenand weather conditions are favourable. The methods of planting are the same as for other small plants except that they are sometimes difficult to plant in narrow crevices between rocks or blocks of stone in a wall. The easiest is to build the plants into place while the or wall is being constructed, but you will have to find other methods if you are planting in established constructions.
See if you can dislodge a rock, introduce the plant, and then replace it. Alternatively, shake a lot of the soil from the roots, scrape soil out of the crevices, and then carefully press the roots into place with a little soil around them. This kind of planting, involving considerable disturbance of the plants, is best done in spring or early autumn when conditions are usually most favourable for re-establishment. Even so, it will probably be necessary to water the new plants well for a few weeks.
Rock plants, being mostly small, are even more in need than most of protection from, which can quickly destroy them. Most must be done by hand but when difficult weeds, such as couch grass, sheep’s sorrel, bindweed and ground elder, become established, you will need . Glyphosate is an almost universal killer which will, in time, eliminate most weeds. Paraquat is rapid in action and particularly effective against grasses of all kinds. 2,4-D kills bindweed efficiently. Make sure you keep these herbicides off the rock plants. The best methods of application are either to use a very small hand-sprayer with the nozzle held close to the weed and a card placed behind it to prevent drift, or to wear a rubber glove with a woollen glove pulled over it; you then dip your hand in a bucket of herbicide and coat the weeds.
Some rock plants, particularly high-altitude alpines, accustomed to being protected in winter by deep snow, suffer badly from wet in winter in our climate and may need to be covered with cloches or sheets of glass. Leave these open at the sides to permit free circulation of air and no undue rise of temperature that might cause premature growth. Apart from this, the main requirement is for protection from slugs and snails. You can either go out at night with a torch and pick them off, or put down metaldehyde or methiocarb slug baits from time to time. Alternatively, place beer in partly covered containers; the slugs are attracted to the beer, find their way in and drown themselves.
Here is a short list of rock plants:
Achillea Some are large plants for borders; there are also small carpeters such as Achillea argentea with white flowers and silvery leaves and Achillea tomentosa with yellow flowers and green leaves.
Arabis caucasica A trailing plant with abundant white flowers in spring. There is an even more effective double-flowered variety, named ‘Plena’, and another, named `Rosabella’, with pink flowers. All like lime and are excellent forand sunny banks.
Small hardy kinds suitable for shady include Cyclamen coum, pink to crimson flowers in winter and spring; Cyclamen europaeum, rose pink or carmine, summer flowering and Cyclamen hederaefolium, often called Cyclamen neapolitanum, with ivy-like leaves and pink or white flowers in autumn
Dianthus Some kinds are too large, too short-lived or too sophisticated. Recommended are Dianthus alpinus, with carmine flowers displayed on a mat of green leaves; Dianthus deltoides, a slender-stemmed sprawler with pink to deep carmine flowers; Dianthus gratianopolitanus, with grey tufted leaves and pink flowers and Dianthus neglectus with rose-coloured flowers on hummocks of narrow leaves. All like lime.
Gentiana Easiest to grow of these rich blue-flowering plants are the summer species Gentiana freyniana, Gentiana lagodechiana and Gentiana septemfida. Spring-flowering Gentiana acaulis, with large blue trumpets, does not always flower freely. Gentiana verna, with small intensely blue flowers in spring, likes to grow in moist peat among limestone rocks. The autumn-flowering kinds Gentiana farreri, Gentiana sino-ornata and the hybrids require an acid, peaty soil.
Gypsophila repens A small gypsophila with white or pink flowers. All forms like lime.
Hypericum The big shrubby kinds are quite unsuitable for rock gardens but there are prostrate or tufted species, such as Hypericum coris, Hypericum olympicum, and Hypericum repens, which are excellent. Hypericum reptans is another fine prostrate species but a little more difficult to grow well.
Iberis The perennial candytufts are all easily grown plants suitable for rock gardens and walls. Iberis Saxatilis is one of the neatest, Iberis sempervirens one of the most showy. Both have white flowers.
Lithosperum diffusum Carpets of narrow green leaves covered in the bluest of flowers for many weeks in summer. There are several selected forms such as ‘Heavenly Blue’ and ‘Grace Ward’.
Phlox The prostrate,kinds are most suitable, such as Phlox douglasii, with white, lavender, pink or crimson flowers, and Phlox subulata, with a similar colour range but a more spreading habit.
Polygonum The two best rock garden kinds are Polygynum affine, which has short spikes of carmine flowers, and Polygynum vaccinifolium, a more sprawling plant with slender spikes of pale pink flowers. Both flower in late summer and autumn and their leaves turn red in autumn.
Potentilla Good mat or mound-forming kinds including Potentilla alba, with white flowers; Potentilla aurea, with yellow or orange flowers; Potentilla nitida, with silvery leaves and pink flowers (but this needs perfect drainage), and Potentilla tonguei, with apricot and crimson flowers.
Some kinds require moist soil and are best grown beside water, but good primulas for rock gardens are Primula auricula, with leathery leaves and yellow, purple or bronzy flowers; Primula edgeworthii and Primula marginata, both with grey leaves and lavender flowers; Primula juliae, with deep magenta flowers, and Primula pubescens, an omnibus name given to hybrids of Primula auricula with flowers in a wide range of colours.
Saxifraga The saxifrages, a large and very variable genus including the mossy sorts which make wide mats of soft green leaves studded in spring with white, pink or crimson flowers on slender stems. All like slightly moist soils and shade from hot sunshine. Cushion or Kabschia saxifrages make firm mounds of grey-green, often rather spiky leaves and have sprays of white, pink or yellow flowers on short slender stems in early spring. They like to grow in sun, with plenty of limestone chippings Saxifraga griesbachii has stouter stems covered in crimson bracts. Silver or encrusted saxifrages have flat rosettes of grey or silvery leaves with loose sprays of white or pale yellow flowers, sometimes speckled with crimson. They like to grow in crevices between limestone rocks. The ‘London Prides’ have rosettes of soft green leaves and loose sprays of pink flowers. They like cool, partially shady places. So does Saxifraga fortunei, with quite large, shining, bronzy leaves and sprays of white flowers in early autumn. Saxifraga oppositifolia is prostrate and creeping, has heather pink or carmine flowers and it prefers peaty lime-free soil.
Sedum The stonecrops, many of which are prostrate plants. All have fleshy leaves and starry flowers. Specially recommended are Sedum cauticolum, with blue-grey leaves and crimson flowers; Sedum dasyphyllum, with tiny grey leaves and pale pink flowers; Sedum kamtschaticum ‘Variegatum’, with green and yellow leaves and yellow flowers; Sedum lydium, with small green leaves turning red in summer; Sedum pulchellum, with green leaves and clusters of pink flowers; Sedum spathulifolium, with rosettes of spoon-shaped, grey or reddish-purple leaves, and Sedum spurium ‘Erdblut’, with green leaves and carmine flowers.
Sempervivum The houseleeks, succulent plants making tight rosettes of green or bronzy red leaves. They need very good drainage and not much soil. Some have rosettes covered in white filament, like cobwebs, but these are more difficult to grow unless protected from wet in winter.
Thymus The thymes, of which the best rock- garden kinds are the completely prostrate, mat-forming, with heather-pink, carmine or white flowers, and , with little leaves covered in grey down. Both can be walked on and make delightful aromatic ‘ ’.
Veronica prostata A carpet-forming species with blue flowers.
Viola Several species are suitable, including Viola cornuta, with light blue or white flowers; Viola gracilis, with deep violet blue flowers; Viola cucullata, with white flowers, and Viola labradorica purpurea, with dark violet flowers and purple leaves. All like cool, partly shady places.