Tufa

Truly a remarkable stone which can be used to make a spectacular rock feature. Tufa is a form of magnesium limestone which is suitable for lime-hating plants — the first surprising feature. Next, it is porous and can hold more than Its own weight of water, and roots of plants will grow Into it.

Pieces of tufa can be used in a scree, raised bed, rock garden, trough etc, but the most eye-catching use is as a piece of pianted-up rock standing on a patio or balcony. The rock is quite soft and can easily be drilled or worked with a hammer or chisel. Make a seriesof downward-sloping holes 1 Vi In. wide and 3-5 In. deep. Use small plants — free the roots from compost and wrap in moist toilet paper and insert in the hole. Carefully fill the space around it with the paving-type planting mixture — see page 9. Water after planting up and keep moist in dry weather. Tocut down the need for watering you can Insert the bottom 1-2 In. of the rock into a bed or rock garden — tufa soaks up water like a sponge. The biggest surprise of all is that some difficult alpines will grow in tufa but may fail under all other conditions in the garden.

ITie dividing line between rock garden plants and the other sorts grown in the garden is extremely blurred The reason is simple — nobody has been able to produce a satisfactory definition of a rock garden plant, which means that nobody can be sure just where the rockery list begins and ends.

There Is no problem with the alpines — an enormous group which is at the core of any rock garden plant list. I n fortunately 'alpine' is often used to cover all plants recommended for the rockery, and that is incorrect. This term has a specific meaning Alpines are herbaceous or sub-sbrubby plants which were originally collected from mountainous regions such as the Alps. Andes, Himalayas, Rocky Mountains etc. The natural home of the True or Highmountain Alpines is above the tree line. The Edelweiss of the Swiss Alps has become the classic representative of' this alpine group — low-growing and extremely hardy wit ha passion for sun anil gritty, free-draining soil. Many alpines appear in the following pages — Saxifraga, Alpine Poppy, Lewista, Erinus, Androsace etc. 11 may seem surprising that some plants from the high mountains may require the shelter of an alpine house to protect them from the rain and frost of the British winter. The reason is that at home these plants spend the cold months lucked up under a thick blanket of unmelted snow.

Alpines make up a vital part but not all of the rock garden plant list. Rockeiy plants include species from the sea-shore, such as Frankenia, and others from woodland regions — Gaultheria and Vaccinium are examples. Many of the specimens you will find on the 'alpine' bench at your garden centre have no natural home — they are man-bred hybrids or varieties.

We must go beyond the alpines if we are to cover the full span of rock garden plants. Alpine and many lowland herbaceous and sub-shrubbv perennials are grouped together as the Rockery Perennials, and nearly all the plants you will buy and grow belong here. The ones chosen for inclusion in this section are not necessarily the best or the easiest to grow — they are the plants you are most likely to find in the catalogues, garden centres and text-hooks. Be careful if you plant Cerastium, Aubrietia, Alyssum saxatile, Arabia and Saponaria. They are easy to cultivate hut their invasive habit means that delicate types can be quickly ovemin if these rampant species are not kept in check. The height and spread information given in this A-Z is what you can expect after 3 years' growth under average conditions.

Dwarf Conifers are an excellent way of providing an evergreen skeleton to the rock garden. Species of Chamaecyparis and •Juniperus are included here, but there are others — look for Pinus mugo *Gnom\ Picea man an a 'Nana', Taxus baccata 'Standishii' and Thuja occidentals 'Hetz Midget". Make sure that the conifer you buy is labelled as a 'dwarf variety. Dwarf Shrubs are another useful group for providing a woody backbone to the rockeiy. A number of the popular ones are included in this section, but you can also grow dwarf species and variet ¡es of Azalea, Berheris, Be tula, Pernettya, Prunus, Rhododendron, Rubus and Salix.

Dwarf Bulbs are an essential pan of rockery planting and many varieties of the basic spring-blooming trio (Crocus, Narcissus and Tulip) can be found in any rock garden catalogue. Iris, Cyclamen and Oxalis are also included here, but there are many others to choose from — Allium, C'hionodoxa, Eranthis, (lalanthus, Leucojeum, M 1.1.scaii. Scilla etc. Ferns were all the rage in Victorian times and still make a useful addition for the rock garden of today — look for Adiantum and Aspienium species.

So what is a rock garden plant?The definition — A plant which looks at home and i,s at home in a rock garden is too restrictive. Some need the protection of an alpine house and there are others which require the humus and shade of a peat bed to be successful. Another definition - -.4 Imv-grmving perennial grown by alpine gardeners — seems to beg the question. The definition adopted here is — A plant you can expect tn find listed in some of the alpine nursery catalogues and some of the text-books on nick garxlening. Not really satisfactory, of course, as il leaves out the annuals and biennials which are so useful to provide a splash of temporary colour — Antirrhinum, Bellis, Cheiranthus, Helichrysum, Umnanthes, Nemophila etc. Perhaps the absence of a clear-cut definition is a good thing. A rockery is an ait form and should not be shackled by tedious scientific restrictions.

PROPAGATION: Sow seeds under glass in early spring.

SITE & SOIL: Requires well-drained gritty soil in full sun

PROPAGATION: Sow seeds under glass in early spring

SITE & SOIL: Requires well-drained gritty soil in full sun

J. communis

'Compressa

JUNIPERUS Juniper

Juniper is the star of the rockery conifers — the low-growing types with their tiered branches provide excellent ground cover. Juvenile leaves are Heather-like but adult ones are tiny green scales. Thecones aregreen and berry-tike. made up of fleshy fused scales One of the most popular garden Junipers is the Pfitzer (J. media Pfitzeriana'J, but It is too vigorous for most situations.

VARIET1£S: The Spanish Juniper iJ.saiwna Tamariserfolia' i is an old favourite — horizontal branches of feathery foliage with an 0-1 Oft spread if left unpruned but only 1 ft high J. horizontals is even smaller (height 6 In., spread 5 ft) and the leaves have a distinct bluish tinge. J. communis 'Depressa A urea' is a 1-2 ft high spreading bush — golden In summer and bronze in winter There are a number of others which will not exceed 3 ft when mature — choose from J, media 'Okt Gold' (golden, spreading). J. squamata ■Meyert* (blue-green, upright with drooping branches! and J. communis 'Com press a' (greyish-green, column-like),

SITE & SOIL: Well-drained acid soil — thrives best in full sun.

PROPAGATION; Plant stem cuttings in a cold frame in autumn.

LEONTOPODIUM Edelweiss

You will find Edelweiss described in every book on rock garden plants, and it is listed in most alpine catalogues. This is not due to its beauty — many more attractive plants hardly get a mention. The simple reason is that Edelweiss is the symbol of the Alps and their flowers, ti is an interesting rather than an attractive plant — greyish-white, flat flower-heads are borne on short stalks above the greyish-green leaves. It flourishes quite happily if the site is sunny and well-drained

PROPAGATION: Sow seeds under glass in early spring.

LEWISIA Lewisia

Lewis and Clark were the first explorers to cross and map America from the Mississippi to the Pacific — this alpine of the Rockies honours Lewis and the annual Clarkia honours his partner. Lewisia is one of the most colourful of rockery plants — flowers in pink, peach, orange or white with petals which are often striped. Unfortunately, it is not easy to keep alive in the rockery as water in the heart of the plant causes it to rot in winter. The answer Is to plant Lewisia sideways in a crack or crevice, to cover the plant with glass during the winter months or to grow it in an alpine house.

VARIETIES; L. cotyledon is the most popular species The basic details are height 1 ft. spread 9 in., flowering period May-June Choose one of the showy hybrids, such as the 'Sunset' strain The other species are more difficult to grow and are not really reliable outdoors L. brachycatyx blooms in May and L. rediyiva bears 2 in. wide Rowers in June. The aristocrat is L. tweed yi with 2' z in. wide apricot blooms in April and May

SITE & SOIL: Requires well-drained gritty soil in full sun

PROPAGATION: Sow seeds under glass in early spring

L alptnum

L cotyledon

VARIETIES: You are likely to be offered only a single species — L. alpinum The basic details are height 6 In., spread 9 in.,

1 lowering period June-July. The narrow leaves are hoary on top and densely woolly below Tney form a rosette from which the llower stems arise. The curious flower-heads are about

2 in. across — a central group of small, rayless Daisy-like flowers surrounded by a number of long, flannel-like bracts The variety 'Mignon' is recommended — more compact and longer-living than the species

SITE & SOIL: Requires well-drained gritty soil in full sun

J. communis

'Compressa

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