Alpines

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 The Royal Horticultural Society and the Alpine Garden Society define an alpine as any plant suitable  to be grown outdoor in a rockery, or in an unheated alpine-house (cold greenhouse), or frame. This includes all dwarf plants, which are hardy enough to be grown in gardens throughout the British Isles.

Purists will define alpines as plants growing above the tree line, which in the Alps is 5/7000 feet(1500/2000m) and 10/12000 feet (3/3.6000m) in the Andes. Odd though it may seem, many of the high altitude alpines do not thrive outdoors in the British Isles and are usually found growing in alpine houses. This is due to their being covered with a layer of frozen snow during the winter months, giving them a cold, but frozen-dry, winters rest. In this country winter, rain and inconsistent temperatures will often cause the plants to rot.

 Even so, there are a number of high altitude alpines suitable for most well drained rockeries and if we combine these with the numerous dwarf perennials and shrubs, which grow below the tree line you will find an enormous variety of plants from which to choose. There are also a very wide range of very dwarf conifers to choose from, many having originated as ‘Witches Brooms’ (dwarf abnormal branches) on larger growing species.

 Alpines and mountainside plants require good drainage. Many grow in the crevices of rocks, or even on broken rock screes. If you have visited alpine areas you will realize the reason they manage to survive during the growing season, is due to the melting snow, which gives them a constant supply of water. In addition, the evergreen forms have prostrate, or dome shaped habit and foliage, which is thick and waxy, or hair covered to help reduce desiccation by cold wind.

 Many rockeries are badly constructed, usually a pile of surplus stones are covered with soil and then pieces of rock jammed in. Rain and frost will cause the soil to settle, usually downhill, leaving the roots of the topmost plants exposed. Such mounds also dry out quickly during the summer months so that only the deep rooted or succulent species survive. Always build a rockery from the bottom upwards, by first setting in rocks to form an irregular wall, with the occasional outcrop, then infill with 50/50 loam and sharp gravel. A second tier of rock can then be added leaving 9/12 inch (22/30cm) almost flat planting pockets. If room allows add further tiers. A surface mulch of pea gravel will not only ensure the surface around the plant is well drained, but when it rains, it will also prevent foliage and flowers being splashed with soil.

 Many alpines, dwarf shrubs and conifers are evergreen; these will give year around effect. Deciduous alpines will need their dead removing during the late autumn, if allowed to remain it will rot and often affect the crown of the plant. Most dwarf alpines resent competition from weeds and other rampant plants. Evergreen rosette forming plants such as silvered Saxifrages will die if a thick layer of weeds envelopes them.

 A number of alpines and dwarf conifers are suitable for growing in troughs and other containers, and can look very effective when placed on a patio. Always ensure that containers have drainage holes in the bottom, also a lay of broken crocks, or gravel to give added drainage. Fill the containers with 75 per cent John Innes No3 compost mixed with 25 per cent sharp gravel. A two-inch (5cm) layer of gravel or slate will not only add to a containers attraction, but also help to prevent vine weevil beetles from laying their eggs in the soil.

 Dwarf conifers and late summer flowering shrubs can be pruned in April and early flowering shrubs as soon as they have finished flowering. With evergreens, only prune back to where there are still leafs and growing buds. If pruned into old, hard wood they will often die.

 We are not alpine specialists, but grow a wide range of dwarf conifers and shrubs, which are available year round. A good range of alpines (or should we say rockery plants) are also available from April to late summer.