A Czech Style Crevice Garden. I am in the fortunate position of having a glasshouse which I use for growing alpine plants. When I first erected the structure I put in extremely strong staging as I wanted to create plunge beds into which I could put my pots of plants. The staging is made from 900 mm. by 600 mm. paving slabs resting on reinforced concrete lintels laid across brick walls. The staging is 2m.70cm. long and 600 mm. wide and on both sides. Since then I have grown fewer and fewer alpines in plant pots, preferring to have them either outside in the rock garden or planted in an indoor bed in the glasshouse.
After listening to a couple of lectures on modern techniques of growing alpines I began to play with the idea of making a crevice garden. Strangely enough the lecturers showed the same sort of garden though one talked of it as the way ahead and the other as a rather ugly construction. Still I rather liked the idea and it did appear to be a successful way to keep some of the high alpine treasures alive.
Perhaps I should explain what is meant by a “crevice garden.” Imagine standing a row of paving stones on their sides about 25mm. (1in) apart and filling the space with compost right to the top so that only the top edge of the slab remained visible. Plants are then placed in those created crevices and as in nature their roots are forced to grow downwards rather than spreading out. The result is that the plant has the fast drainage alpines like, while the depth of soil means that there is moisture deeper down. The narrowness of the crevice and again the depth of the soil also means that the soil temperature remains fairly constant, neither too hot in summer nor freezing solid in Winter.
I decided to use hyper-tufa and to cast it into flat blocks of about 25cm. square and 25mm. thick. The reasons for using hyper-tufa are that it is lighter than straight forward concrete, it is reasonably easy to make and cast into shape, it is cheaper than buying rock and the ingredients are easy to come by. We priced the construction using some rather nice cast concrete slabs and they alone came to well over £250, just for them alone, before soil, gravel or plants. I made the hyper-tufa for less than a fifth of that.
Making the Blocks. The first thing I did was to make a mould from 25 mm by 38mm roofing laths. The mould was about 750 mm long by 250 mm. wide and 25 mm. deep. I made three moulds like this. I placed the mould on a bed of sand and lined it with plastic. The plastic was to prevent the mixture sticking to the sand and also to make removing it from the mould easier.
The mix I used was 1.5 parts sifted coir to 1 part sharp sand and 1 part cement. I found that the standard mix of 2 parts coir was not strong enough. Water was added to give a consistency which allowed me to spread it out in the mould. When the mould was full, it was left for a few days to go off.
When it was hard enough I removed the mould. I also marked where I wanted the block to split into three pieces. Again the piece was left for a few more days before being split. I used an old saw to do this as the pieces were still too soft to handle safely. If I had had more space or time I could have left them to go harder before splitting up.
Finally the pieces were stood up to finish off drying. I brushed over the smooth surface left by the plastic to make a more natural looking finish.
All in all I made 42 castings like this to give me 126 blocks with which to make the crevice garden. It took about six weeks from start to finish.
Once all the blocks were made they were stood up on the glasshouse floor to dry out properly.
I was fortunate enough to have found some ridge tiles in the garden. These I split and they provided support at the back of the staging. I also left about an inch or so of the original sand plunge on the staging as support for the blocks until the soil was added.
Construction Being the impatient type I did not wait until the blocks were completely dry, but started building when they were hard enough to handle without them breaking. I had made some hyper-tufa rocks as an experiment before hitting on the idea of making moulds, one of these I used as a corner piece. I used a piece of 25 mm. wide roofing lath as a spacer and to get the crevices parallel to each other.
After a few false starts the best looking arrangement seemed to be at an angle across the staging.
I also used the tallest blocks at the rear and sloped the construction slightly to the front of the staging. There is no particular need for a slope like this, but it does make looking at the plants from the path a lot easier. At the same time I tried to avoid having all the rows of blocks exactly the same height to make it more visually interesting. After a lot of moving around it eventually finished up looking like this.
Filling the Gaps. To fill the crevices I used a mixture of two parts of a compost made from ground bark and sterilised soil to one of Perlite and one of 5mm. grit. This is the standard mix I use for growing most of my plants.
I did not add any fertiliser as there is a small amount in the compost and I do not want the plants to grow too big by over feeding them.
The next job was to water the compost and press it down into the crevices. It needed to be firm but not solid, so this was a delicate operation. I also had to avoid moving the blocks as the soil in the next crevice was not firm enough to hold the blocks in position. All I need now is patience. I will have to give the compost time to settle down and for any weed seeds to germinate and the plants removed before planting.
