Signs of spring in rock gardens

Press, 9 August 1985, Page 14

Signs of spring in rock gardens

Gardener’s « DIARY

Derrick Rooney

One of the sure signs that spring is arriving is the welcome emergence of tiny tufts of green leaves in the rock garden where the charming Lewisia nevadensis was growing last year.

Many gardeners underrate the charms of this little plant, a member of an exclusively American genus of alpine plants with bright flowers, fleshy leaves, and drought-tolerant, succulent roots.

It’s a tiny thing, growing only 6cm to Bcm high. The leaves are transient, emerging in spring, completing their cycle fairly rapidly, and often shrivelling away before the flowers have finished.

The root is a fleshy storage organ, parsnip-like but much smaller, and it needs gritty, rich soil, with sharp drainage at the neck. Some forms have glistening pure white flowers, and some have a dash of green. Individual plants are short lived, but seed freely, and in a suitable place a colony will reproduce itself for years.

Some of the other species are not so accommodating, and have caused gardeners all sorts of bother, but with a bit of care most of them can be conquered.

A clue to their cultivation may be found in the American descriptions of lewisia habitats which suggest that most of the 16 known species prefer steeply sloping ground or shady rock faces. Thus an ideal rockgarden site rnignt be one where lewisias can be planted on their sides — either in a dry-stone wall, or in a crevice between two rocks.

Vertical planting in this way ensures that any rain which falls on the rot-prone rosettes is shed immediately, and gardeners who have observed plants growing in the mountains know that it is often the position in which plants prefer to put themselves.

Many lovely but touchy alpines — ramondas and haberleas, for example — suddenly become easy to grow when planted this way. But a point to remember is that a southerly face is better than a sunny one.

Look on the shady side of any alpine outcrop or bluff and you will see a dramatic increase in the size and diversity of plants. With a few exceptions, plants on sunny faces are there because they can survive drought and heat, not because they insist on it. Even a difficult plant like Lewisia tweedyi — the giant of a gem of the genus — can be persuaded to flourish if suitable habitat can be made for it.

This sumptuous lewisia has bold, leafy rosettes from which it unfurls, for many weeks in summer, a succession of large, clear apricot flowers. Alas, it is short lived in most gardens, and even the Americans regard its life span as a mere four or five years. The most popular garden lewisias, the cotyledon hybrids, have flowers in shades of pink and rose, in large sprays. They are nominally evergreen, though most of the older leaves usually die off in winter. Some are not the easiest of plants to grow, but are worth a bit of effort.

Opinions differ about what constitutes suitable conditions for these lewisias, but necessary ingredients seem to be good soil, abundant moisture at the roots in the growing season, and extra-rapid drainage at the collar. Lewisia pygmaea is one of the lesser species, but has

a long life expectancy. Its name may be misleading, because it is bigger than Lewisia nevadensis and considerably bigger than L. Columbiana' var rupicola, although it is quite small when compared with L. tweedyi or L. cotyledon.

Some reference books make uncomplimentary remarks about L. pygmaea, based on descriptions of the wild forms, but that needn’t deter gardeners because the horticultural version is a nice plant. Its small rosettes of narrow, roundish leaves disappear in summer underneath sprays of silky, pale pink little flowers. Even better is the hybrid, “Pinkie,” raised in England by that great alpine gardener, Will Ingwersen, from a cross between L. pygmaea and a cotyledon hybrid. “Pinkie” is not much bigger than its mother, but its flowers are more substantial and the pink is deeper and clearer. Readily propagated by cuttings, it makes a perfect trough plant. An interesting comment on “Pinkie” is that although the various lewisia species (L. tweedyi excepted) hybridise readily in gardens, only a handful of hybrids have been named. A reason for this is that it is difficult, among the cotyledon hybrids, to find one which is sufficiently different from the others to justify a name.

One exception is “George Henley,” imported by a Southland nursery. This cotyledon hybrid is a freeflowering lewisia whose ground colour, described in the catalogue as brick red, is gently overlaid and striped with apricot. Gardeners’ Queries

Mr Mike Lusty is away on leave. His Gardeners’ Queries column will resume on August 23. Queries, and well-wrapped, good-sized samples, should be sent to Mr M. Lusty, 56 Wayside Avenue, Christchurch 5.