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Kent Alpine Gardener's Diary

This entry: 28 May 2015 by Tim Ingram

'...it approximates closely to the same thing.'

'Should anyone ask me "What do you consider the most necessary adjunct to the modern rock garden?" my answer would be, unhesitatingly, "The Scree", scree or moraine or even a sand bed if you like, it approximates closely to the same thing'. 

(Walter E. Th. Ingwersen, 1933)

 

'Rock gardening is great fun. I have built myself several small rock gardens... with bricks and stones and cement and logs of wood, when I had no better materials, and grown good plants on them too. Anyone who cares about plants and understands them can do the same'.

(Frank Kingdon Ward, 1948)

*****

There was a time when alpine gardeners made screes. Screes were the thing. Moraines, complex ways of channelling moisture; deep excavations and carefully constructed layers of sand and gravel, crushed brick, scoria, ashes, mixed with a soupçon of leafmould or peat. Inhabited by wonderful collections of plants growing well depending on care, upkeep, inclination and climate. Subject to drought, storm, blackbirds, moles and voles, and the quizzical and restless eye of horticultural fashion, and yet very successful when carefully made and maintained and unquestionably satisfying for the gardener. Then came rocks, their natural partner, arranged haphazardly, dramatically, geologically, Orientally, economically, and sometimes pleasingly and perfectly clothed with plants. The heyday of rock gardening? And later, alpine houses, pots, Shows, plants grown to perfection, novelty, rarity, judging and botanical erudition, mountain holidays and photography. 

In fact all of these things have inevitably run together along with the practical experience of horticulture that underlies them. The aim of course is to learn about the plants, understand them, grow them well, share this with the quizzical and restless eye of fashion - as far as this allows - but most of all to gain pleasure and enlightenment from alpine plants in the garden, alpine house and Show.

Nowadays the crevice garden and sand bed have replaced traditional rock garden and scree, the same things in different guise, and are equally successful in growing alpine plants well - in some hands brilliantly. Horticultural fashion still only occasionally glances at these plants, even in 'that classic country of amateur plantsmen' (W. Schact, 1963), where roses, perennials, camellias, rhododendrons, dahlias, sweet peas and snowdrops generally garner more attention. So just as you have to climb up high to discover them in Nature, you have to search diligently to find them in gardens, and in both cases they are more than worth the effort.

*****

This is only meant to be taken as literally as the reader may or may not want to take it. However much you may want other gardeners to find the same interest in plants as you do, everyone's garden is their own. It does though serve as an introduction to a very simple and successful way of growing many choice alpines - the Sand Bed. The sand bed is no more than the simplest of screes, generally lacking even the addition of any leafmould or humus - though this will be naturally incorporated over time from the plants themselves. Its great benefit is that it enables a wide variety of otherwise challenging alpines to be grown in the garden at little cost apart from energy and imagination, and negates the criticism that these are only plants for the specialist. It is so easy to make and so spartan that many gardeners will find it hard to believe that it can succeed, so these are some pictures taken over the four or five years that our sand bed has been established (and there is more information in my and other articles in the AGS Journal).

This is a view across the Sand Bed this spring.

In the background the dwarf Helianthemum canum and Veronica thymoides merge together rather sympathetically. Erinus alpinus is one of the few things that has seeded onto the tufa, except for a few frustrating weeds, and could be taken as a good a definition of a rock plant as anything else, even the famous 'rock-breaker' itself, Saxifraga. Next to it in a small hole is a tiny long-rooted seedling of Aquilegia jonesii - watch this space... In the background are the appropriate flowers of Daphne x hendersonii 'Marion White', growing with Origanum laevigatum which gives colour later into summer.

Daphne x hendersonii 'Marion White'

Alpine Campanulaceae are especially well suited to sand - many don't start flowering yet but Edraianthus pumilio is a real star and seeds around gently. It can have wonderfully compact glaucous, almost silver, foliage, or looser, greener leaves - both showing the natural variation that occurs when you grow many alpines from seed. The second picture is E. horvatii, bringing out all the charms of the genus, and one which is worth exploring in greater detail.

Edraianthus pumilio Edraianthus horvatii

Silver saxifrages are legion and well suited to sand, in contradistinction to most others which will not tolerate drying out. A whole bed could be devoted to these alone, for their foliage is as enticing as their flowers. This one, S. 'Canis-dalmatica', is especially good at the moment and a good incentive for us to grow a wider variety.

Saxifraga 'Canis-dalmatica'

Small penstemons such as P. newberryi ssp. sonomensis, are frustrating beauties amongst alpine plants - seemingly ideally adapted to the sand bed but so prone to die back in our overly humid climate. This is a genus more than worth experiment - probably in a bed with year-round cover. There are few alpines more appealing. Here the 'American Foxglove' growing with the 'Fairy Foxglove'.

Penstemon newberryi subsp. sonomensis

This pairing of Rhodanthemum 'African Eyes' and Lithodora oleifolia has gone from strength to strength over the six years since they were first planted (I'll show a picture from back in May 2009 later on).

Rhododanthemum 'African Eyes' & Lithodora oleifoli

Many Boraginaceae come from hot and dry habitats - good for sandy soils - and Masha Bennett's book on the family, published in 2003, is an excellent botanical introduction, covering very many rarely encountered plants as well as the much more familiar ones of its title. Here I have placed the book with Lithodora x intermedia in the garden, and really there is no way you can separate books and plants can you? The two have unique synergy.

Lithodora x intermedia

Amongst onosmas, which are often short lived plants, O. albo-rosea stands out in every way and most especially because it can be a good perennial when perfectly sited. Not the most comfortable of plants to extract seed from! A second that we are growing in the same place, and which Masha Bennett tantalisingly pictures but doesn't describe in her book, is O. polyphylla; just one plant from wild collected seed and fascinating amongst all onosmas I have grown in having a deciduous habit. A genus amongst so many others that is worth exploring and putting on the map - garden or otherwise.

Onosma albo-rosea Onosma polyphylla

And finally from the borages, a small plant of Paracaryum racemosum (slightly going over), which Jon captured so nicely amongst his photographs from the Wimborne AGS Show. I don't know what chance there is of this succeeding in the garden, and it is likely to be relatively short-lived, but there is a thrill in discovering these rarer plants and growing them, and to know about them is to cherish them if that is not too emotional a word.

Paracaryum racemosum

Near to the paracaryum grows in increasing clump of the 'Rusty Back' Fern, rather beautiful all year round. Several xerophytic ferns prosper on the bed and suggest the prospect of a more distinct bed devoted especially to these, with the possibility of winter protection to widen the range of species grown (especially the cheilanthes). These are commonly seen as fine specimens at the Shows but I have only rarely seen them growing outside in the garden - though no doubt there are specialist growers within the BPS who grow them like this.

Asplenium ceterach

And in part of the bed where the sand is less deep is this perhaps less than brilliant combination of pink and yellow daphnes - D. cneorum and D. calcicola - which has been flowering over a long period.

Daphne cneorum & Daphne calcicola

Not in the same bed, but growing in very similar conditions, is a small plant of the exquisite N. American Aquilegia scopulorum. Aquilegia is another genus perfectly suited to sand with its deep questing roots, often self-sowing freely, and the smallest of species such as this are wonderful plants, very distinct from much else on the bed. This one is definitely not so easy to establish as many but who wouldn't try looking at those flowers? (There are a whole number of very interesting American aquilegias, which Graham Nicholls describes in his book on N. American Alpines, which can light up a 'miniature' garden landscape just in the way that larger species do the garden proper).

Aquilegia scopulorum

So here is the bed this spring. Relatively small but full of colour for many months and a good source of cuttings and seed of a great variety of plants. Some winters it has been covered with glass lights; last winter it wasn't, but few if any plants were lost desite a bedraggled appearance of some in spring. It is extraordinary how much interest a bed like this can create, and it may slowly be converting some of our visitors to growing these plants more extensively.

This is a picture of the bed six years earlier, a year or so after it was first made and planted. Very few plants have been lost in the intervening years, though a few over-run by their neighbours, Here you can see the lithodora and rhodanthemum next to the formidable rapier-leaves of Yucca whipplei, which flowered magnificently several years later and then died. As a plant to weed around it was not appreciated, and here of course was where all the weeds were! The blue in the background is Polygala calcarea 'Lillet' and the pink, Androsace studiosorum 'Salmon's Variety', both highly recommended.

...and a couple of years later as the bed was being extended.

And what are all these plants growing in? This is the sharp sand used, a horticultural potting grit available in Kent which is derived from crushed flint. It is very sharp and variable in particle size up to 5 or 6mm. Nothing at all was added to this apart from the soil plants were growing in when planted (loosely shaken from the roots and mixed with the sand). Over time the underlying soil - a foot or eighteen inches down - has been  brought up into the bed by ants and worms but to no greatly appreciable extent. Some plants have been very slow to establish, and certainly watering needs to be watched earlier on, but later even in hot weather it is possible to feel moisture on pushing a finger two or three inches into the sand and the dry surface limits most weed seed germinating. Because we use this as a source of propagating material the bed is watered in  protracted dry spells and occasionally topdressed with Vitax Q4 fertiliser. Otherwise it looks after itself far more effectively than much of the rest of the garden and I can see some of the surrounding areas eventually being cleared and planted in the same way.

(Here, to put this entry more into context, is my reflection on Walter Ingwersen's article in the AGS Bulletin on screes. This is copied from 'Any Other Topics - Random Nuggets from the Bulletin'  on the Discussion Pages of the website).

'Should anyone ask me "What do you consider the most necessary adjunct to the modern rock garden?" my answer would be, unhesitatingly, "The Scree", scree or moraine or even a sand bed if you like, it approximates closely to the same thing.' (Walter Ingwersen, 1933).

 

In the 1930's many alpine gardeners were writing about screes and moraines, and just like the crevice gardens of today this sharing of information must have helped stimulate more members into discovering that growing alpines wasn't just the preserve of the expert few. But it was the expert few who persevered and experimented with different growing conditions and freely shared their knowledge. Earlier, more complex moraines with subterranean watering were constructed and described in rock gardening books, the idea being to mimic the freely flowing water at depth in mountain screes. However, these were not effective and Walter Ingwersen 'found in a very long practice that the underground watering is not necessary, and may be a source of danger'.

 

Nearly the whole of Bulletin Vol. 2, No. 4 (December 1933) was devoted to the scree, both in Nature and in the garden. If you are used to double digging you will be less put out by the advice to dig out 2 to 3 feet (or even more on heavy soils) before infilling with scree mixture. (In the small sand bed I have just made I removed ca. 12 to 18 inches, and this was a huge amount of work! A small excavator is called for and would do the job easily and quickly - but what to do with all that soil?) Walter Ingwersen describes a wide variety of gravels, grits and sands with which to make a scree, the coarser materials requiring proportionately more leafmould or peat added to aid water retention. At Branklyn, Perthshire, Dorothy Renton used river gravel/sand and leafmould/loam in the proportions 5/1. Will Ingwersen advised 75% stone chippings to 25% leafmould and sharp silver sand, and recommended that 'The real enthusiast will want two screes, one for limestone loving plants, and one for those preferring a granitic soil.' Certainly that would be good, and experimenting with different conditions for different plants is the essence of success. In the wetter climate of central Ireland pure limestone chips or red sandstone/leafmould (5/2) were both recommendations.

 

Pictures of the flat screes at Edinburgh Botanic Garden and at Branklyn, show how very effective these are, and allow many very choice plants to be grown. At Edinburgh in a dry climate the yellow American Lithospermum canescens, species of Onosma, various lewisias (including rediviva) and many saxifrages and gentians thrived. At Branklyn, many of the same plants and primulas like the beautiful and strongly scented reidii. Not with standing these, however, very many fine alpines can be grown by the simple expedient of planting in 4 or 5 inches of gravel over soil, as shown by Robin and Sue White at Blackthorn Nursery; more choice species being grown in raised beds and tufa. The ground level scree though is aesthetically very pleasing and effective for otherwise very tricky plants, and is ideal associated with a rock garden, even if few gardeners construct these in the 21st Century.

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