Creating a Scree Garden – Rocks, Stone and Gravel in the Garden
In nature, a scree is created by material continuously breaking away from a mountain under the weathering action of frost and depositing itself on a slope which is also on the move downwards. The process results in the build-up towards the base of the slope of a mound, many metres deep, of variously-sized stones. It cannot be recreated exactly in a garden but a compromise is possible.
A garden possessing a gentle slope can be used to make a rock garden, or raised beds but if the site lies in full sun building a scree which is relatively easily maintained, is a wonderfully effective way of growing small alpines. The site must have plenty of water in spring and summer to flow down to good at the base. The whole site should slope between 1 in 10 and 1 in 20, sufficient to give a natural fall and to drain well in autumn and winter, when water is least needed.
If the slope is too great, the scree will move too easily and, without a continuously crumbling back-up mountain to replace it, the top of the scree will disappear. The stone building up at the base is not moveable because of the plants growing along and across it.
A scree with a good depth of coarse and finer stone mixtures, combined with large stones to give a bold effect, can support a great many plants, and all of them should be in full sun. The possibilities include small-leaved cushion and mat plants, trailers, and fairly sparse shrubs, the whole creating an effect of peace and tranquillity and, above all, the impression of more space than there actually is. This can only be achieved in two other forms of gardening, the alpine lawn and the pavement. Unfortunately, there are few scree gardens around for you to see – all the more reason for making one.
The shape and size of a scree depend on the kind of garden into which you are putting it. The size is not important, but the scale is. A large scree in a small garden is not a good idea as it will look very flat but a scree up to approximately half the length of an open-plan garden, 10 metres (30ft) long, can be impressive. However, if your garden is enclosed, scale down the scree to a third of the total length of the garden. Unlike the rock garden and, one scree bed per garden is sufficient.
The best shape is to have the sides gently curved and the top and bottom ends dependent on the shape of the overall site. A wide site can have one curved and one squarer end (at the top); or if the site is long and narrow, both the top and base can be squared off. A scree can fit in ideally with a formally paved area at the top or base, or both, because plants can flow across the edges of the formal areas softening their lines.
The scree is basically very simple to construct but good preparation is even more vital than for any other ~ form of construction in this site. Unlike rock gardens and, is not the most suitable side edging, especially where the top and base of the scree are paved, otherwise the site becomes harsh instead of flowing. Grass is probably the best material for the surround but be warned that the need for good grasses, and no creeping grasses and other weeds apply even more here, since there is no barrier to prevent invasion of the scree bed from the surrounds.
The site can be marked out simply by laying a rope or thick string round the prospective area and then cutting out the area marked to a depth of 50cm (20 inch), without using stakes first. Then remove the, turf or whatever covers the ground, to another part of the garden. Loosen the remaining soil with a fork before adding fresh soil in stages to prevent running over the loosened soil with the barrow.
Fill half the total depth with a soil mixture containing equal parts (by bulk) of leaf-mould or peat, large shingle up to 2.5cm (1 inch) in diameter and loam. If the soil is inclined to be sticky and heavy, use equal parts of leafmould or peat and shingle, with no loam. Where the soil is limy, use a limestone mixture throughout and avoid acid-loving plants. Top up all sites with gravel; from 2.5 to 5cm (1 to 2 inches) sized grains. These chippings may be acid or limestone depending on whether the plants are to be mixed limestone and acid-lovers or just limestone plants.
The scree may be left like this but it will look more impressive and offer cooler root conditions for many plants if stone is added. Select from the types of stone used for rock gardens and raised beds and match them to the gravel or chippings. In this case, though, there is no need to match the strata and line exactly and the stones can be laid individually or in small groups, to give the impression that they have just fallen down the mountain. However you cannot just throw them in anyhow. You will have to give some thought as to how each one is arranged. Those with strata should be laid as for rock gardens, with the line of strata almost horizontal to the ground and the whole stone leaning back gently into the slope. Rounded and irregular stones can be used to give character to the otherwise flattish site; smaller stones aid good drainage.
It will be of further help to use some stones as stepping stones, to prevent too much pressure from being applied to the smaller stones around them. As they do not have to support any soil, use smaller stones than in a rock garden. Remember to avoid the ‘Almond Pudding‘ and other horrors of stones sticking up like sore thumbs! You can vary the final arrangements to suit your tastes, using from three to dozens of stones and covering up to one third of the surface area.
Maintening a Scree Garden
Maintenance work of course is all at ground level, so a scree garden is not recommended for other than reasonably agile people. However, with the large volume of stone and the shallowness of the soil, the weeding problem is greatly reduced, making this kind of garden an attractive proposition. Also, less equipment is needed to build a scree: just a spade, fork, shovel and, where grass is cut out, a half-moon tool also. The only large items needed are a wheelbarrow and a sack truck, which can be hired if necessary.
Watering is easily arranged. You can either use an overhead sprinkler over the whole site, or lay a hose (with a small rose attached) on the ground at the top of the scree and, with the tap on at half pressure, allow the water to flow down the site. The second system is ideal for a long narrow site on heavy soil, and can be modified to suit individual sites. Watering can be done discreetly by burying the hose permanently underground, exposing it at the end where it waters the site.
Water as and when necessary and only then. As with all rock garden sites, it is better to do the watering in the evenings as this allows the moisture to be retained instead of being taken up by the sun. A good long soaking is always preferable to an infrequent dribble of water.
The Base of the Scree Garden
I have not mentioned the arrangements for the base of the site until now because they depend on the type of soil. Heavy soils require special arrangements and must drain to an even lower level when there is a lot of rain. Adequate drainage can be ensured by laying a single line of drainage tiles across the base of the site, on top of the soil mix, firmed down to the same level as the base of the stones laid on top of the soil.
Laying the tiles above soil level will ensure that the site never dries up completely. To allow for occasional cleaning, lay an inspection cover at the top end of the drainage system.