Reprinted from The New Zealand Alpine Garden Society Bulletin

I am the editor and wrote this article with help from the best at Wrightman's Alpines. It works so well. Until I discovered this technique the free draining media would inevitably leak out before the plants could establish and they could only be stated at the top or central position of a crevice.

Clay, Crevice and Cleft

HARVEY WRIGHTMAN, EDITOR SUZANNE PICKFORD 

The Wrightman Nursery is based in New Brunswick, Canada and is run by Esther Wrightman. Sadly Harvey passed away in 2016, but his legacy lives on in his wonderful postings on the Wrightman Alpine website which we have been graciously allowed to access I wanted to share with you this wonderful method to give our chasmophytic plants the best chance despite the hot or wet conditions we often experience.

I have always admired the vertical, cleft formations that are so often seen in Czech trough and alpine gardens and imagined that they must be painstakingly constructed and slow to mature. Regardless, I was interested in knowing the process, and having Josef Halda, a Czech Botanist and enthusiast crevice gardener visiting the nursery, provided an excellent opportunity to learn.

As it turned out, the whole affair was far easier than I imagined, and the results accrue very quickly. Once I had seen the process, I wondered why I had never been able to figure it out. It was that simple. When I explained to Josef what I wanted to see, he went to the tufa yard and chose quite ordinary-looking stones that could be split along the sedimentation lines. Tufa is readily available in other parts of the world, it is a soft, porous, often water deposited mix of minerals containing mostly calcium carbonate and a much smaller percentage of other minerals Water saturated with calcium chloride oozes out of hillsides or vents, the material precipitates forming a type of special limestone that has layers that can easily be split. The best for rock gardening is quite open with many air spaces.

In New Zealand we can try our limestone but it tends to form more amorphous layers of considerable depth. It too can be easily worked with simple hand-tools like an old saw, drills and chisels and a hammer. -Ed

Our tufa was from a denser, layered formation that splits on its rift lines quite predictably; and, Josef indicated that it is very similar to the stone they have in the Czech Republic. The breaks are clean and angular making it easy to bring pieces closely together. For a trough, one piece can be split into 2 or 3 pieces. These pieces are book matches and wil then form the basic crevice(s).

To glue the slabs togther a paste of clay is made with some sand added.

We used Spanish River Carbonatite as its grain size was acceptable and it would provide added nutrition. In New Zealand we could add pumice of limestone fines, the later will provide some nutrition and would be good for calciotrophs. While one could dig clay from the backyard, it is easier to buy bagged clay from a hobby store. Measure out 3 parts clay to 1 part course material and mix the 2 together thoroughly as dry materials. If these are not available you can use more elbow grease and mix in to wet clay, slowly mix in enough water until a sticky paste is formed. Using a flat spatula, the clay paste is applied to one or both side(s) of the crevice to ~ 10mm thickness.

Now the daring part, for us Josef did this outside during a week when it froze solid every night, and all the plant material was from the heated green-house! The plants were bare-rooted whether they be cutting, seedling or potted plant. The roots were splayed out on the smeared clay, the crown set just above the crevice. The matching piece is then gently brought into contact, and the 2 were pressed/tapped together to eliminate any voids.

Although the use of clay seems counter to most published advice regarding "drainage", elevating the piece will ensure that over saturation never occurs.

Watching Josef choose plants and where he placed them was also very instructive, as he has a huge amount of actual field experience. Many of his choices were new seedlings from the winter's sowing, including some Eritrichum aretioides, Gentiana spp. and Androsace spp. from West China. He was very happy to see them and have the use of them. All were lined up in the crevices - both vertically and horizontally, adding dimension to the planting. Useful too, are small mat/cushion plants such as Arenaria spp., Silene acaulis, Gypsophila aretioides and Salix spp. In these mats, Gentiana spp., Primula spp., and others will grow comfortably in these mats, again replicating what will happen in nature.

The great thing about this method is it intuitively directs you to place things.

To make the verticals work, you need small mat-formers, available from Ortel.nz, such as Androsace, Draba,  Asperula. and the ultimate plugger Sempervivum cultivars of the tiny sort. These plants spread quickly enough to stop erosion. They are small enough that other, showier plants can grow through the mats. Semp's which are so easy to establish are especially good. Once they outgrow their usefulness, they can be removed with little disruption. The mats provide a good foil to set off the choicer plants.

As a bonus, lots of sensitive species can be grown this way. Perhaps even more importantly, the stylistic side of culture is greatly enhanced. The use of vertical plantings produces drama, and even quite ordinary plants become riveting when displayed this way.

The method used does take a little nerve and daring, just think, the Czechs were doing this so many years ago.

Below: I love building mini crevice gardens in troughs using light weight hypertuta rocks which can be made very thinly. This method has been revolutionary in terms of success for plants, where once small pieces were artfully compacted in gaps to hold mix, which would then proceed to leak out with even gentle watering.

Note the crevice on right compared to that on the left. The clay-bound crevices allow the full length of the crevice to be planted and effectively increasing the depth of the trough. Seemingly without check the plants grow straight away and with vigour.

I look forward to trying the technique on a larger scale with concrete waste or "urbanite".

Photographs Suzanne Pickford