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Crevices - the way to the future for alpines?

What a fantastic talk given by Kenton Seth, the visiting Crevice Garden Master from Colorado at our Thursday evening meeting. The membership was treated to a clear, concise and interesting run down on the art and craft of crevice gardens around the world. Thus inspired, four lucky members arrived at the Botanic Gardens Historic Rock Garden to create the crevice garden taught and lead so ably by Kenton. The Botanic Garden's rock garden was originally created in 1939, with huge rocks arranged beautifully in the traditional style. Grant Matheson who is in charge of this section has begun the huge task of renewing the extensive but elderly heather and heath collection, and has propagated the old varieties and placed them in a new area surrounding our crevice garden site. He has also begun cleaning up and replanting the rest of the rock garden - quite a task. He prepared the site for us and bought in the rock, so efficiently collected by club members a couple of weekends ago from Halswell Quarry, and ferried in members' trailers to the gardens. Reopened especially for our project and under strict supervision from the Council herpetologist (lizard and gecko watch) and staff, 29 pallets of rock, including some huge slabs, were wrestled from the quarry face in a huge and haphazard pile of shattered plates.

Piles of tools and heaps of sand were ready on the open and empty site. Kenton explained his overall plan, basing the shape of the beds on the faces and facets of the rock itself. He was very conscious of working in such an established site and was at pains to ensure our work would fit within the extant design.

Key large rock slabs were placed and held by digging in first. This allowed us to use the large pieces efficiently without, for example, finding we had too many of them in just one section. It also ensures that we were able to build more like real uplifted rock faces. Larger slabs with smaller pieces breaking and eroding from them.

It was important to pick a compass setting, in this case, 330 degrees to ensure a consistent alignment that would form a cohesive whole. We really appreciated the importance for this as the build progressed. Kenton was careful to build in both fine and larger planting crevices. Some with sites in the deep shade on the southern side of rocks, others on hot dry faces, and some in a well on the top. The occasional bulges or "bubbles" as we coined them, of rock were designed to mimic the massifs of the rocks in the existing garden with striated rocks as a setting. These strata were carefully drawn and maintained throughout the design, a line set by the large slabs were continued across the garden at exactly the right angle. Being strict with our angles meant as we built with a section and into the next, the line was always successfully maintained and worked visually. These lines are very important in the scheme and were a beauty to behold as the work was completed.

Kenton then set to work on the edges, Small "cliff" faces were created around the edge, undulating so that it was never an unchanging line, but evolved gradually. It was important to find just the right rock with its uppermost face and outer edge lining up in a plane. This gives the look of a large rock having been broken by time, repeated freeze thaw cycles cracking and opening fissures. This outer line was purposely broken and set back from time to time in a natural manner.

It was essential that most of the rock was buried and pieces locked together so that the structure is strong, safe to garden upon and will last for years to come. Backfilling with sand was only done once the rock was locked. So as the sand went in, packed in with sticks and pins, it became stronger still. If sand was added too soon it would push rocks out of alignment and prevent good bonding and pleasing placements by pushing against an unsupported rock slab, tipping it slightly.

The overall design “leaked” out of our designated bed in a natural manner and will eventually be joined by a section across the gravel path. It will be linked by a "river" of stone used as paving across the gravel.

Members arrived on the third day as the work neared completion to hear the rationale and see the benefits of this style of gardening. Kenton showed the construction process and then lead us through planting some of the crevices.

By washing the roots to prepare the plants they were able to fit into small slots to become one with these tiny crevices seeking shelter down deep. Leaves and stems will be safe from damp and rot, yet water is easily found deep within the crevice and in the subsoil up to 1m beneath.

One needs to be careful as the new plants establish of course. But once securely in place, they are remarkably drought tolerant and require little maintenance. However Kenton pointed out that we should not choose plants with uncontrollable runners, rampant growth or site our crevice garden in a dandelion drift zone for example. Top dressing with a matching gravel of a range of sizes is the most natural and beneficial to plant growth. Keeping the small chips of the parent rock to add to purchased gravels would be the most effective.

The Society was very fortunate to be able to benefit from Kenton's experience and evident skill with his chosen medium, rock.


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