The Rock Garden

There is often a mystique and a complete misunderstanding as to the why, the need and the purpose of a rock garden. The novice will often be under the misguided notion that to grow rock plants/alpine plants, necessitates the construction of a rock garden. In fact, nothing could be further from the truth; raised beds, troughs and the alpine house are perfectly good alternative ways of growing alpine plants with great sucsess, without the use of great quantitys of rock.
Having said that, a rock garden is obviously an attractive and desirable feature to add to any garden, providing the plants and rocks are seen in context and harmony together, and the whole thing has an aesthetic and pleasing appeal. But get it wrong and it is nothing more than an eyesore; a pile of stones haphazardly placed on a mound of earth positioned in a dark ugly corner in totally unsuitable conditions. The plants will struggle to survive, and will eventually die, and the creator of such monstrosities will bemoan that the failure is due to alpine plants being too difficult to grow anyway! The picture shown above, of the R.B.G. Edinburgh, is of a rock garden on a grand scale incorporating many tons of very large rocks in a setting of an acre or more of garden. Very few of us would have the space or monetary funds to embark on such a project, but we can all take ideas and inspiration from good garden design and construction.

Do be wary of the great amount of bad advice from some of the so-called gardening “experts” that you may come across in print and especially on the internet. The unattractive example shown right is typical of rock garden construction promoted by some people on the internet; some even go so far as to make a video of this sort of work! The rocks are placed in a circle, usually incorporating an area of about 10 square feet (0.93 square meters) and isolated in the middle of a lawn, with a few rocks spaced equally distances apart from each other; or sometimes considerably more, piled up into a mound, disparagingly and rightly referred too by Reginald Farrer as "a dog's grave". These very same gardening “experts” recommend planting such rampant and invasive plants as - Campanula poscharskyana, Cerastium tomentosum, Euphorbia cyparissias and Sedum acre in such a small area. Looking at the picture to the right again, shows how artificial the rounded stones look in this poor excuse for a rock garden; ideally, they should be angular in shape, with a distinct strata line, and with each one closely butted up to the next. So let us now move onto the next stage….

Choosing AND PREPARING the site

All too often, the decision to construct a rock garden is done for the wrong reason. If you have an area in the garden that you consider is shady, damp and poorly drained where nothing will grow, a bad spot and an eyesore; and as a last resort you think a rock garden will solve the problem……then forget it!
If on the other hand you wish to grow some of the most gorgeously beautiful plant you will ever see – alpine/rock garden plants, and you want to give them the best conditions you possibly can…..then go for it!
A bit of thought should be given to where the rock garden should be sited. In deciding, take into account the following requirements that you will need.
1) An open aspect.
2) Freedom from perennial weeds and tree roots.
3) A pleasing integration with the rest of the garden design.
4) Good drainage.
5) Possibilities for future extension.
Giving careful thought to the above five requirements will avoid many future problems.

There is a huge amount of advice given by very many people on various ways of building/constructing a rock garden; some of this advice is good and some is not so good!
I do think that the bigger the area you can devote to a rock garden the better…so think BIG! On the whole, the majority of rock garden plants/alpines are easy, and unlike annual bedding plants, they will last and thrive for many years. Keep the smaller choicer plants for troughs; the bigger more robust plants for the rock garden. Good drainage is essential, and it may be that you will need to incorporate sharp sand and gravel, working this to a depth of about 45 cm (18”) and at the same time removing all perennial weeds. Do consolidate and tread down the soil to avoid subsequent sinking at a later date. You may have to add more soil to your site to achieve the level you want.
Choosing the Rock
It used to be said, that if it is at all possible, it is always wisest to use a local stone; this was in the days when there was not a great choice of stone to be had, and few garden centres had much choice. Nowadays, many garden centres have an immense choice of various types of stone, and it can be quite bewildering for the novice to make a wise choice. You can get green, plum and blue coloured slate; there is black and red larva rock, orange moon stone and even a green translucent glass rockery stone. Then you have the more traditional stones, like Cotswold, and the various limestone, sandstone and granites. All these stones have their matching grits, and you will also come across grits that have stark outlandish colours of white, yellow and blues etc. Whilst many of these so called innovative rocks and grits are used and promoted by the more ‘Avant-garde’ garden designer, along with coloured plastic balls on bamboo canes, mirrors, stained glass and ‘modern’ sculptures in stainless steel and wire bound bamboo etc; I feel that this is completely out-of-place with the cultivation of alpine plants. You may sometimes come across rock gardens constructed from reclaimed smashed masonry, broken concrete slabs and smashed-up breeze-blocks. These are no more than unacceptable substitutes; and in my opinion, should not even be contemplated!
The two pictures above show a choice of four different rockery stone on offer at a local garden centre. You will perhaps notice that very many of these rocks are much too small and awkwardly shaped to be used in making an attractive feature for a rock garden.
Whatever type of stone you decide to use it will be quite expensive, and whilst one ton may sound like a large quantity, it will only make a very small rock garden. Another important factor is the size and shape of the rocks. If you can pick up a rock in one hand it is most likely much too small, (with the exception of tufa rock). Ideally, you want pieces from 30 kilograms up to and possibly a little over 45 kilograms in weight; at a very rough estimate that would be about 25 to 30 pieces per metric ton.
Now onto the shape of the rocks; if they are pyramid shaped, wedge shaped or oval/round shaped, you will have great difficulty in placing them to look natural, no matter which way you try them! You want them to be roughly rectangular in shape with each face close to right angles (90 degrees) to the next. The bulk of your rocks should ideally be about 46cm x 23cm x 23cm (18" x 9" x 9") in dimension. You won’t of course be able to get every rock at this rectangular size, so you use smaller and irregular shaped ones to build up to this size. You can use longer and deeper rocks also.
It is worth mentioning at this point that once you have decided on what type of rock you would like for your rock garden, do make sure that the garden center/supplier has a good stock, and that the same rock will be available in the future should you wish to extend your rock garden. Do not make the mistake of just ordering a quantity and leaving it to the supplier to pick out the pieces for you; pick out each piece yourself, place one piece to the next, and then another, discard those that are too small or badly shaped. Try and visualize how each piece will look when viewed from different sides, and remember that the faces that are buried need not be square to the others. Once you have picked out your pieces purchase them there and then and take them home in your vehicle with you, or have them delivered, getting assurance that they will be the pieces that you have chosen.
BUILDING A Rock GARDEN
It’s a good idea to sit down at the table with a pencil and a sheet of paper and sketch out your rock garden, if you use graph paper you can scale the distance from pathways and other garden features; the shape of your rock garden can be almost any shape you wish, but avoid a square symmetrical shape with sharp corners, use gentle curves and make it look natural. One of the most pleasing shapes I have seen of a rock garden can be best described as that of a dog’s hind leg!
Your design will depend, up to a point, on the contour of your garden. If your garden, or part of it, is on a gentle slope you can build terraces, which step up from one level to another; and if that is the case you can have the rocks flat as shown in the picture left. If you decide to build terraces on a flat site you will have to tilt the rocks so that when the rocks are seen “face-on” the back of the rocks are tilting at an angle into the soil. It is important to maintain the same angle of tilt for every rock you put in. I feel that this is always difficult to do, and at the same time achieve a natural look to the rockwork, but in the hands of a skilled and experienced builder of rock gardens it can very often look attractive and natural. Do avoid a double tilt; in other words if you can see the “face-on” rocks looking south and you then walk round the other side of the rock work and view it to the north, the “face-on” rocks can’t be seen.
Do bear in mind that very steep angles of stratification, of about or near to 45% do occur in nature as do various angles between; right up to horizontal angles of stratification. Rock falls are frequent in mountains all over the world. There are a number reasons or factors that can start a rock fall; changes in the climate like freeze-thaw, the movement of surface and ground water, external stresses and root movement are some typical causes. It might start by the movement of a relatively small rock, but the tumbling and bouncing of this one rock can cause other larger rocks to become dislodged, and they in-turn cause other rocks to fall down the sub-vertical slopes of a mountain to finish up as a huge rock fall of many tons at the bottom creating a talus or scree, where all sizes of rock, from huge boulders to small pebbles will finally settle. The picture right shows how a rock fall might look, with all sizes and shapes of rocks in compleat disarray. This then, is one of natures way of creating a “rock garden”, plant and soil debris will also be washed down the scree slope to provide food and nutrients to the seeds of plants that will eventually find a home amongst this rock rubble. It is very often difficult to create this natural chaotic look in cultivation without it looking too artificial and unnatural.

The picture left shows an attractive scree viewed from its lowest point and the well placed rocks don't look too obtrusive and unnatural. This is in a large garden in an open aspect and contains dwarf conifers and shrubs as well as many choice alpine plants. The vertical face of the rocks as seen from this view are not much more than 12 centimeters high and the back face of the rocks slope into the soil.
Click on any of the three images below to see a bigger picture.
The larger of the two rocks shown here is 90cm long, 26 cm at its widest point and is 22 cm deep. (Having about 2 cm below the soil level)
 The combined length of these two rocks is 110 cm, 28 cm at the widest point and 22 cm deep. (Having about 2 cm below the soil level)
The combined length of the two rocks shown here is about 82 cm, 26 cm at the widest point and 22 cm deep. (Having about 2 cm below the soil level)
 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Images scanned by www.slidesondvd.co.uk using the Nikon Super Coolscan 5000 ED