A Boulder Garden.
Over the last twelve months or so in doing various pieces of work in the garden we have uncovered a number of rocks. These range in size from small fist sized ones to boulders 50 cms x 50 cms x 50 cms. Most of them are rounded boulders rather like the type you would find on a beach and like beach stones, our boulders are of equally diverse origin. From our sketchy knowledge of geology we believe that our rocks were deposited in this area during the last Ice Age, when apparently our garden was at the bottom of a huge lake.
At first we were a bit concerned that these and the others we have excavated over the years might have been of archaeological significance. There is a spring at the bottom of the garden and springs were often considered to be sacred in past times. Also according to the local Ordnance Survey maps there are supposed to be Celtic field markings in the area. However, in almost every case we have found modern rubbish underneath the boulders. So unless the Romans invented corrugated iron, white glazed pottery and HP sauce we feel pretty confident that we have not disturbed anything of historical value.
We rather think that these rocks have been brought in from the surrounding fields and dumped on this land to keep them out of the way of the plough.
The Boulder Collection
It seemed a pity not to find some use for these rocks. We have already constructed a conventional style Rock garden elsewhere in the garden, using pieces we dug up earlier.
The Rock Garden.
We have also used a lot of the smaller fist sized rocks in various other places in the garden, either as retaining walls or to repair and extend the existing ‘cobbled’ paths or as ground cover.
The Cobbled Garden and Walls Stone Mulch
So we were looking for a different use for our finds. After reading various articles in the journals of different societies dedicated to growing Alpines, we decided to attempt to create a crevice garden. Our aim was to put our boulders together in such a way as to suggest the jumble of boulders that might be left after a glacier had retreated, a glacial end moraine, albeit on a much smaller scale. That way the diverse origin of the material which we had to use was not a problem. In a glacial moraine the material deposited would reflect the geology of the country over which the glacier had travelled.
The piece of land we had available is about 3.5m long and 2m. wide at the top and narrows down to about 1 m. at the bottom. It faces North West. It is protected from the early morning sun by the boundary hedge that runs along the 2m. edge. On the long side is a trellis fence . To prevent the hedge from encroaching on to the construction I dug a trench and built a concrete block wall. On top of the wall I placed a 1.5m high woven panel fence.
From the North Side From the west.
The soil here is a gravely peat based silt. I cleaned it of weeds, mainly couch grass and ground elder using a chemical weed killer. It was dug over and left untouched for Winter. I then skimmed off the top layer of soil to use later on and brought in some brick rubble to act as filler. This material will be hidden by the boulders and will also act as extra drainage.
I then back filled behind the first layer of boulders with a mixture of brick rubble and top soil, taking great care to fill all the crevices with soil.
Work then proceeded with the next layer of rocks used being slightly smaller. Again the space behind was filled with brick rubble.
More soil and rubble were added. Rather than use precious boulders as the back of the construction, I built a wall using old house bricks to retain the soil and to stop it actually touching the fence or the trellis.
The third layer was made using slightly smaller boulders. We were fortunate in having a large number from which to choose.
As before soil was added as infill. As we were getting to the desired height, I did not add any brick rubble to this layer. The soil I am using is full of gravel anyway so I felt it was not necessary to add extra grit at this stage.
Finally the top layer of small stones was added, leaving the structure with a slightly domed top. As you can see from the photographs, it was getting towards the evening by now.
Not a bad days work for my wife and I.
The next morning I spent making sure that all the crevices were well packed with soil and that none of the rocks was loose. Since there has been very little rain here I gave the whole structure a good watering to settle the soil. Finally I covered the soil with 5 mm, alpine grit.
Now all we can do is to wait for it all to settle and for the inevitable weeds to appear. Once they have been removed then comes the exciting part, buying the plants and planting it up.
