Rock Landscaping Ideas – Flat and Sloping Sites

rock landscaping ideas

Rock Landscaping Ideas

Rock Gardens and Their Surrounds

Mowing the grass and maintenance of the ground around many rock gardens will be a problem, unless there are paving slabs, or stone paths between the rock garden and the lawn. Grass has a habit of creeping up and round but not through stone. The material for this purpose need not be the same as for the construction but it must be level and look reasonably similar and informal. The slabs should not be rectangular; but should be at least 30cm (1 ft) wide. If the depth is shallower than 8cm (3 inches) they can be laid on a bed of concrete to prevent movement but the concrete should not show.

To do this, roughly pattern out the stones for the site, then set them aside in order. Lay a bed of concrete 10cm (4 inches) thick. Press each stone into the mix. Before the cement sets press a layer of rubble and stone chips left over from the rock garden construction between the stones so that they lie below the surface. Laying stones on cement will inhibit the growth of weeds of any size; smaller weeds and grasses can be prevented from growing at all by applying a pre-emergence weedkiller early each year. Take care not to get any weedkiller on the lawn or rock garden. The level of the completed paving surround must be below the surrounding grass to enable the mowing machine to run over the slabs and not into them.

Keep the surrounding grass from creeping towards the rock garden by regularly trimming it with edging shears. Using a half moon-shaped tool each winter will make the edging easier to maintain during the growing season.

If there is a border of bare soil 8cm (3inches) wide, between the paving and the grass, this will help to keep down the risk of perennial weeds. Maintenance then means keeping that border free of weeds.

Rock Landscaping Ideas for Flat Sites

When building a rock garden on a flat site, use the largest stones possible and, for practical reasons, use the tallest stones for the bottom layer. Take one of the pieces with the largest top surface and lean it backwards towards the centre of the site. Sink it just below soil level but do not bury it unnecessarily. Remove only the essential amount of soil first; it is better to remove too little at first than too much and then have to replace it with soft yielding soil which may weaken the stability of the stone being laid. When the stone is in position ram it well in before introducing the next stone.

The first stone to be laid is the keystone, from which all the others will radiate on both sides. Each stone must join exactly on to the end or face of the next one, otherwise soil will spill from the upper to lower level and the structure will be ruined. This part of construction takes a lot of time but is well worth the effort.

If the stones are wedge-shaped they can be laid with the thin end behind the last stone laid or in front, thus leaving the thicker part of the stone to, fit into the rock garden and so thickening the depth, see figure 16. Minor obstructions to the line of the stones can be chipped off with a cold chisel and club hammer, or another stone chosen. The tops of all stones must be level to within 2.5cm (1 inch) of one another. If the top is not level, then when the two ends join to complete the circuit, they will not  match up on the top level and soil will spill from the upper level, exposing the back as well as the front of the stone. Check this as your work progresses around the keystone by using a spirit level (see figure 16).

fig. 16

You can build any shape, but angular constructions look more impressive than round ones. Lay each stone with its strata almost parallel to the ground, slightly sloping backwards.

When the first layer is completed, the second and subsequent layers may be added. The base of each layer must begin below the top of the last level, see figure 18 below. The total number of layers will depend on the size of the project and be determined by the proportion.

Try as far as possible to arrange the greater number of surfaces facing south, east and west, for the greatest amount of sunshine and the smallest area facing the north.

Paths through the Rock Garden

rock garden path Larger sites will need paths between the different sections of the rock garden. To decide whether your garden needs a path consider how easy it will be to carry out maintenance work and also whether the plants can be clearly seen from normal ground level, bearing in mind that alpine plants are generally smaller than others in a garden.

A path should be wide enough to allow two people to pass one another – since your handiwork is bound to be shown to others. Gently curved paths are more effective than angular or sharp-cornered ones.

If the water table in your garden is high, build simple paths at ground level but where it is low i.e. 30cm (1 ft) or more below the lowest point on the path, you may use a system of ‘cut-and-fill’ paths as described below, provided that the cut is always above the water table.

Cut the soil for paths on a gentle slope, using the surplus to fill the rock garden but keeping the topsoil above the subsoil. To do this, mark out the paths with long stakes and remove the topsoil from the path and the estimated high points of the rock garden to the outer regions of the construction area. Cut the subsoil from the path at the correct slope (not steeper than 1 in 15) and spread it over the estimated high points of the rock garden. Follow up by replacing the topsoil on the high points. The stakes marking the paths will have to be driven in further as work progresses, to maintain the line.

A prerequisite for this operation is a drainage system for the paths. it is best to attend to this after the paths have been cut as the drains should follow the line of the paths, out to a soak-away (if the garden has one) or to a point lower than the lowest point cut, provided that this would not interfere with other properties.

Next build the drainage system. At the lowest points in the site, build silt traps (see figure 2) and cover each with a channel grating. Lay drainage tiles to the soakaway, or lowest point in the garden. It is not necessary to put a layer of gravel over the tiles here but if you build a soakaway use rubble and hardcore at a lower level than the drain exit and run the tiles halfway into the soakaway, which should be the same area as the ground it drains. Allowing for the heaviest storms, 10 sq metres (12 sq yd) of path needs 10 cubic metres (14 cubic yds) of soakaway. Now you can see why the site must be well above the water table.

The cut-and-fill area will add height to the finished job, so you must take this into account when estimating the amount of stone to order. The bottom layer of stones can now be laid, starting with the keystone, at the lowest point on each path. This time, when radiating outwards and up the slope, the stones  will need to get progressively shorter until one end of the top surface disappears into the ground. The shallower a stone is, the longer and broader it needs to be in order to remain stable. Therefore, use stones of increasing length down the line of the path. As a stone disappears in the soil, begin the next layer with a new keystone – not necessarily in the middle as before but radiating out further each time, see figure 19 below. The keystone should touch the top edges of the first layer and the subsequent stones will again get shallower before they, too, perhaps disappear into the soil. Continue in this way until you reach the level of the original ground then proceed as for the single flat site.

Another alternative to leaving the path bare is to pave it using the same type. of stone as for the rock garden, but note that it is not possible to pave with uneven stones such as Westmorland. The stones should never be shallower than 7cm (3 inches) unless they are bedded on a cement base, otherwise when the corners are trodden on they will dip. Lay the stone as for crazy paving. There is no need to bed any pieces thicker than 7cm (3 inches) on a cement base.

Rock Landscaping Ideas for Sloping Sites

Rock gardens are traditionally grown on sloping sites and if they are done well, they can look most impressive.

The steepness of slope will determine the rate of rise of stone to be laid. The greater the rise, the closer the layers of stones will be and vice versa. As with a flat site, build from the base, even if the site backs on to a wall and the temptation is to start at the top. In that instance it might be easier to use the largest stones towards the top rather than the base.

If you have a large site, access might be made easier by building a gently curving flight of steps. They should be wide enough to allow two people to pass one another, although not necessarily all the way up. Do not build steps on a small site as they reduce the planting area and can look ridiculous.

The best backdrops to a site are informal but obviously a house or outbuilding cannot be disguised. Climbers and wall shrubs can be planted to lessen the stark effect of the walls but as they create the problem of leaf fall, evergreens or even the smaller shrubs and climbers are better still.

Brick and artificial stone walls as part of a terrace are not very suitable as background but if the rock garden can be used as an expanded wall by merging the top layers of stone with the wall, so much the better. You can keep the lower bricks and blocks as long as you make drainage holes at regular intervals as the work progresses upwards. It is too risky, as well as unnecessary, to remove the wall entirely. Do not build the garden against any structure which is not already simply a retainer of soil. A house or garage wall was not designed to have soil and water above its damp course and both would eventually suffer internal damage and possible collapse.

The factors governing the design of a sloping rock garden are the same as for the flat site, except that all the layers have to ‘disappear’ somewhere. Informality can be best maintained by keeping any steps away from extreme ends and middle ground. Give each layer a keystone which should form the highest point for, unlike a flat site, the strata will fall gently to each side, as well as leaning back sufficiently to keep stability. Therefore, the stone will generally get shorter towards the end of the site, or else a gap will appear between the base of the upper and the lower layer (see figure 17).

fig. 17 fig. 18 and fig. 19

There are no rules governing the steepness of steps but it is obviously easier if they are not too steep and a good guide is to make about two and a half times more tread than riser height.

To blend the steps into the layers of a rock garden, two or more steps may be made to merge into one layer, by ‘bending’ the steps round towards the layer. This is the only time in a rock garden that one layer of stone may be mounted on top of another successfully and with a pleasing effect, provided that not too much of the first stone is obscured.

To overcome a steep rise in the  slope, take the steps round the line of contour, or even angle them.

17. October 2010 by Dave Pinkney
Categories: Gardening Ideas, Rockery Garden | Tags: , , | Comments Off on Rock Landscaping Ideas – Flat and Sloping Sites


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