Weblog of Eric

The Dried up River Bed.

There are not many people who can claim that their latest alpine plant growing area

came about because they always wanted a Yew hedge. I have spent many hours in various

National Trust properties admiring and envying the beautiful Yew hedges. Up to the

beginning of last year, there was nowhere in the garden where we could put one, so it

remained a dream. However, while visiting a local nursery we discovered that they were

selling off 3 feet tall yew plants at £15 for ten plants. Now that was just too good an

opportunity to miss, we bought 10.

At the northern corner of our garden we have a small wood. The trees are actually

Damson and the ground under them is full of a Galanthus nivalis form. I wanted to extend the

area in which the snowdrops grew so I spent part of the winter clearing away the brambles

and ivy from the section nearest the boundary. This opened up the wood to the strong winds

which cause a lot of damage to our garden in spring. The clearance also left us with a length

of fence with nothing growing up it. It was just about the right length for the yew trees! I

fastened windbreak material to the wire netting which is the boundary fence to give the trees

chance to establish before they had to brave the icy blast.

Behind the Damson trees.

Now those who have read about our gardening here in other articles will perhaps

remember that the soil in this part of the garden is best described as a mixture of broken glass

brick rubble and leaf mould with a sprinkling of scrap metal. Therefore, I had expected to

have to do a fair amount of work to clean it up before planting. In went the fork, spades are

no use in this kind of soil. Clang! Every where I pushed in the fork, after about 6 inches

depth, I hit something solid. I cleared away the ‘soil’ removing as much of the nasty stuff as I

could while doing it. Just below the surface I came across rocks.

That is not unusual in this garden, almost everywhere we have dug we have found

‘rocks’. They are almost all the rounded pebbles one finds on beaches or in river beds.

The area was once a glacial lake and the fields round us are full of this material. We think that

as the fields have been cultivated, any unwanted material has been dumped on the waste land

which is now our garden. Mind I always worry that we have found something of

There are not many people who can claim that their latest alpine plant growing area

came about because they always wanted a Yew hedge. I have spent many hours in various

National Trust properties admiring and envying the beautiful Yew hedges. Up to the

beginning of last year, there was nowhere in the garden where we could put one, so it

remained a dream. However while visiting a local nursery we discovered that they were

selling off 3 feet tall yew plants at £15 for ten plants. Now that was just too good an

opportunity to miss, we bought 10.

At the northern corner of our garden we have a small wood. The trees are actually

Damson and the ground under them is full of a Galanthus nivalis form. I wanted to extend the

area in which the snowdrops grew so I spent part of the winter clearing away the brambles

and ivy from the section nearest the boundary. This opened up the wood to the strong winds

which cause a lot of damage to our garden in spring. The clearance also left us with a length

of fence with nothing growing up it. It was just about the right length for a yew trees! I

fastened windbreak material to the wire netting which is the boundary fence to give the trees

chance to establish before they had to brave the icy blast.

 

Now those who have read about our gardening here in other articles will perhaps

remember that the soil in this part of the garden is best described as a mixture of broken glass

brick rubble and leaf mould with a sprinkling of scrap metal. Therefore I had expected to

have to do a fair amount of work to clean it up before planting. In went the fork, spades are

no use in this kind of soil. Clang! Everywhere I pushed in the fork, after about 6 inches

depth, I hit something solid. I cleared away the ‘soil’ removing as much of the nasty stuff as I

could while doing it. Just below the surface I came across rocks.

 

 

Now, that is not unusual in this garden, almost everywhere we have dug we have  we have found

‘rocks’. They are almost all the rounded pebbles one finds on beaches or in river beds. The area was

once a glacial lake and the fields round us are full of this material. We think that as the fields have

been cultivated, any unwanted material has been dumped on the waste land which is now our garden.

Mind I always worry that we have found something of archaeological interest, until the ubiquitous HP

sauce bottle turns up, below the pebble layer. So, after a weeks digging and removing this is what I

had. There were also a large number of broken house bricks, slates and other such material. This

 was taken to the local Recycling yard.

The rocks themselves I stored behind the compost heap until I had decided what to do with them.

Fortunately/sadly, early on in the winter we had something of a disaster. The temperature dropped

from plus 8c. in a rain storm to minus 8c, in something around two hours. To show what effect that

kind of weather can have, we lost all our sprouts (vegetables in an Alpine article! Heresy! } and

cabbages. The plants simply exploded. When spring arrived we also discovered that the weather had

wiped out all the hebes in part of the garden. That was quite a blow as they were all grown from wild

collected seeds and thus irreplaceable. However, it did leave us with an area where we needed to do

something to fill the empty space. The area faces South east and is well sheltered from every other

direction by plant covered trelisses.

 

The other side of the path from this was already an area of gravel, which has to be kept that way to

allow access to the Septic tank when it needs emptying. It also was a useful place to put the rocks

before placing them in situ.

 

Then came the problem of deciding what we were actually going to make with these rocks. Most of

them were less than a foot by a foot by a foot. There were 5 or 6 bigger ones and a lot of much

 smaller ones, down to gravel size. Since they were glacially deposited they are of very mixed origin

which makes creating a conventional ‘Rock garden’ a little difficult. We discussed various options with

 one or three ‘experts’ and the best suggestion was made by Vic Aspland. He thought that the

material looked rather like the sort of rocks on found at the top of a beach. That is what we set out to

 re-create.

The first action then was to make a barrier between the new feature and the garden area behind it.

Since it was intended to look like a beach and we had some lengths of logs I made my version of a

groyne.

 

Then we began trying to place the rocks. This was much harder to do that we had anticipated.

 

 

No matter how we tried, it always ended up looking like a conventional rock garden. So after a few

 head scratchings and rock moving around and cups of tea, finally we changed the design a little to

making a dried up riverbed. We placed the largest rocks first.

You need to imagine the water flowing from the top right of the picture, down to the path, through

various little channels. You need a good imagination though!

Now it was just a question of adding the rest of the material.

Since this was to have been a beach scene we had bought a load of ballast to use as filler. This is a

mixture of 25 mm gravel and sharp sand. I also added equal quantities of 12 mm. shingle (rounded

 gravel) to it. This mixture was spread over the area between the rocks. The sand is a rather bright

colour, but it was all that was available. It is river sand so it does not contain any lime.

The next layer was sharp sand and 5 mm. grit in equal quantities.

The rest of the smaller stones were then added. and topped with 12 mm. shingle.

The same sort of construction was continued on the other side of the path, except that since this was

 already a gravel garden and extremely well drained we did no more than scrape the gravel away,

place the rocks and cover the area with sand.

The finished article. Now comes the interesting part, planting it up.

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 1ft square and 1in 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.

Planting

At last the exciting part. I went to an Alpine Garden Society Show at which there were a number of specialist nurserymen. I bought 30 plants suitable for growing under glass at an average cost of £2 each.

There actually is a technique used for planting up a crevice garden like this.

As you can see the original plant in its soil is wider than the gap in which it is to be planted. Also the soil in which it is growing is far richer than the soil in the bed and it also contains slow release plant food granules. I am also (after one or two bad experiences) a bit suspicious. In the past I have found both vine weevil grubs and root aphids in newly acquired plants. I hasten to add that this has never happened with plants from the nurseries at this Show.

 I gently removed as much soil as I could from the plant without damaging the roots. There are some plants which would react badly to this treatment. It would be unwise to treat Daphne for example like this or Acantholinum. It is wise to check in the books for the words, "does not like root disturbance" before one proceeds. I used a 2.5cm wide spatula to scrape away the gravel mulch and to dig a hole for the roots, making sure the hole is big enough for the roots be spread out

The roots are gently spread out in the hole and a little of my own compost used to cover them. The neck of the plant is left a little way above the soil level.

The gravel is then replaced, carefully tucking it under the leaves so that the neck of the plant is covered and the plant itself is sitting on the gravel. The whole process is repeated for the other plants. Mind, £60 does not go very far in a bed this size. Hopefully they will grow and I can add more later

Pictures to be added!

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 Path 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.

A Beginning                          Rock Selection

The first layer of rocks was put in. We selected the biggest to form the base of the construction, mainly for reasons of stability. In a real glacial deposit the boulders are much more randomly placed. There was no attempt to stratify the boulders as this was not necessary and in any case most of them have no obvious right way or wrong way up.

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.