Submitted by gsparrow on Mon, 06/22/2020 - 10:40
Cyndy Cromwell

I’ve BEEN A gardener my whole life, but only became interested in rock gardening after relocating from Connecticut, where it’s possible to grow a wide variety of alpines, to the challenging conditions of Raleigh, North Carolina. Here, summers are hot and humid and winters are mild, with little snow. In Raleigh, I began attending NARGS Piedmont Chapter meetings at the JC Raulston Arboretum. Then as now, Bobby Ward, our chapter’s Program Chair as well as NARGS Executive Secretary, was bringing the very best speakers on horticulture to our area. Hearing talks by Panayoti Kelaidis, Ian Young, Mike Kintgen, and others, I became more and more interested in rock gardening.

In 2016, I enjoyed attending the NARGS AGM in Denver and Steamboat Springs, Colorado. The following year, I got to know some wonderful alpines in Wyoming and Montana on a NARGS study week with Mike Bone and crevice garden guru Kenton Seth, whose stunning creation in Arvada, Colorado, I had visited earlier. Seeing my first Saxifraga oppositifolia with Mike Bone remains one of my lifetime horticultural moments. I began to understand the mania for growing mountain plants at home, though I wasn’t sure that was possible in the North Carolina Piedmont region.
Around the same time, Tony Avent, of nearby Plant Delights Nursery and Juniper Level Botanic Garden in Raleigh, began construction on what was to become an enormous crevice rock garden using “urbanite” or recycled concrete. The early stages were built by others, but most of the construction was done starting in 2017 by Jeremy Schmidt, Grounds and Research Supervisor for Juniper Level. Tony seemed to be trying all the alpines, and a lot of other plants thought to be ungrowable in Raleigh. I was surprised and excited to see that many grew very well indeed in the new crevice garden. Given the drainage and growing medium they needed, these plants were unaffected by the summer heat and humidity.
I began volunteering in the crevice garden at Juniper Level while construction was still in progress, at first working on “crevice dentistry,” that is, filling the gaps in the crevices with Jeremy’s customized PermaTill (heat-expanded shale-gravel) mix. Now that construction is complete, my main job is removing weeds, especially the horrific Euphorbia maculata. Volunteering at Juniper Level has been a wonderful experience for me and I’m grateful to be allowed to work in this superb garden. I have learned so much, but the most important lesson was that it is possible to make a wonderful rock garden in steamy Raleigh. It was only a matter of time before I asked Jeremy to build a crevice garden for me.

The Build
The consultation process with Jeremy was unusual. He visited the site, and we talked over Diet Cokes about ideas for installing a crevice garden in an existing car pullout space dug into the hill above my driveway. Jeremy didn’t do drawings or estimates. Instead, the project developed organically as construction progressed. I had never undertaken a major landscape project in this way but trusted Jeremy’s design and engineering capabilities after getting to know him at Juniper Level.
The wish list for the project was short. I wanted the crevice garden to look as natural as possible in the space as if underlying ledge rock had been exposed. A seep for growing plants that required moist, well-drained conditions was the only other request. The overall design concept was summarized by Jeremy: “I was simply creating movement by recreating a glacial boulder flow that was perpendicularly cleaving off a stratified uplift.” Easy for him to say, and to do!
We began with materials selected at a local stone yard. Jeremy preferred to use stone of varying dimensions and from different quarries; a total of thirteen pallets of three types of flagstone and three size classes of boulders were used. In his skillful hands, the result is a dynamic, vibrant look for the garden. Three large boulders, each weighing between 800 and 1200 pounds (360 to 540 kg), were selected. Once positioned, the other elements of the garden played off these three anchors. The planting medium used here was somewhat richer than at Juniper Level: 75% PermaTill and 25% topsoil/compost mix.
With the aid of a skid steer rented for one weekend, Jeremy was able to accomplish the project very quickly. He worked in several stints fitted around his full-time job.. Jeremy confirms my impression that fully one-third of that time was spent in contemplation, mentally putting together the complicated stonework jigsaw that became the garden.
In order to make the garden an integral part of the existing landscape, it was important to consider transitions – both from an adjacent formal raised bed and from the existing woodland behind the crevice garden.
I’m particularly happy with the transition between the existing formal stone retaining walls and the crevices; it appears as if the wall just tumbled over itself and into the crevice area. The other transition, between the crevice and the woodland garden, has evolved over time and has been achieved mostly through plantings. With leftover boulders and flagstones, I’ve tried to work in features that give the impression that there is underlying rock continuing into the hillside, eventually dwindling to just a few outcroppings. Plantings help to soften and naturalize the effect, I hope.
The seep is simply engineered, with PVC pipe run down from an uphill well and skillfully concealed by rocks above the main seep boulder. Gravity carries the water downhill, so no pump is needed. I dislike the sound of splashing water in the garden, so the flow is set at a low volume. The water cascades silently over the boulder, now almost covered in bright green moss.
Stepping stones for access
Jeremy’s design was thoughtful. He installed a set of stepping stones in such a naturalistic way, that I didn’t realize they were there until I began climbing up and down the slope installing plants. I appreciate this feature every time I work in the garden.
Shady crevice garden
Another successful feature, which I hadn’t requested, is a small pocket of shady crevice garden off the northeast corner of the house. It’s located across from the main crevice garden, separated by the pathway leading to the back garden. There was an existing downspout feeding into the driveway, but stones and planting medium piled around the drainpipe conceal most of it. The area is now planted with Acer palmatum ‘Twombly’s Red Sentinel’ and Kalmia latifolia ‘Pristine’. They’ve done nicely for a couple of years now, their growth restricted by the tight location.

So which plants perform well in a North Carolina crevice garden? Eventually, I hope to grow some of the more esoteric alpines, but the aesthetics of the garden were important to me, so I began the garden with some easy and reliable components. Epimedium ‘Amber Queen’, Dianthus ‘Bath’s Pink’ and Iris cristata ‘Eco Bluebird’ remain reliably cheerful in the first planting area.
Experimentation, with its disappointments and surprising successes, happens everywhere else. There is a long list of failures, including plants from genera I would like to try again in different areas of the crevice or using different species or cultivars.
Since the garden is new, I’m still trialing many of the plants, especially those started from NARGS Seedex seed. That said, I’m fairly confident the plants listed below would work for other southern rock gardeners, having performed well for me over the last two years.

Many of the conifer genera suited to the south, like Podocarpus, Cryptomeria, and Chamaecyparis, are available in dwarf sizes and have been doing well so far. They are wonderful for punctuation in the garden and year-round plant interest. Some of my favorites are Cryptomeria japonica ‘Vilmoriniana’, Chamaecyparis obtusa ‘Bess’, and Chamaecyparis pisifera ‘Cumulus’. A few conifers that don’t usually do well here have worked in the crevice garden, like Pinus sylvestris ‘Watereri’.
Holly species are quite happy in the North Carolina Piedmont; I especially enjoy the dwarf Ilex ‘Rock Garden’ and Ilex crenata ‘Brass Buckle’.
A thread leaf Nandina domestica ‘Aka Chirimen’ struggled in garden soil for years, then perked up and grew beautifully in the shady crevice. Also in the shady crevice, a tiny Rhododendron keiskei ‘Yaku Fairy’ is a sweet accent.
Mahonias aren’t known as crevice plants, but there is a noticeable difference in the vigor and appearance of two silver seedlings of Mahonia confusa planted at the same time, one in the formal raised bed, the other nearby in the crevice garden.
Having had some success with Daphne odora in the garden, I added five alpine hybrids and Daphne tangutica to the crevice. Two of the alpines have died; the others look healthy but haven’t yet bloomed. I remain hopeful, for now.
Raleigh’s zone 7b climate accommodates a nice variety of succulents, which appreciate the excellent drainage in the crevice garden. Most of these plants would not do well in my heavy red clay soil but are happy in the well-draining PermaTill mix.
The curly starburst shape of Agave bracteosa ‘Squidget’ tucks into nooks and crannies nicely, as does my favorite Mangave ‘Man of Steel’. Two dyckias, ‘Pale Rider’ and ‘Grape Jelly’ echo the starry fireworks. Silvery Graptopetalum paraguayense never survived a winter before planting in the rock garden, and now makes little rows of shimmering buns along the crevices.
A variegated yucca, larger in scale, punctuates one end of the main crevice. Opuntia humifusa was much too happy in the crevice and had to be removed; but I appreciate how well other opuntias, like O. wrightii (syn. of Cylindropuntia kleiniae) and Opuntia fragilis ‘Potato’ perform in the loose medium. Notocactus species and hybrids, prickly little buns perching among the rocks, are budding up now in April, and promise to bloom later this spring.
Delosperma cooperi and D. dyeri have done well, the lone survivors of a massive ice plant experiment, prompted by my favorite nursery offering an amazing selection of cultivars at rock bottom prices. It was interesting to note how quickly most varieties melted in the heat of summer, but I’m grateful for the two growable species.
Sedum species have been excellent for adding interest and texture to nooks and crannies. I’m especially fond of low growers S. confusum, S. japonicum ‘Tokyo Sun’ as well as larger S. palmeri, with red-tinged foliage and yellow blooms in early spring. Orostachys species are also easy and happy here.
Bulbs, Corms, and Tubers
Many bulbous plants prefer the crevice garden. In Raleigh, it’s all too easy for them to rot in heavy clay soil. I’m finally able to keep Cyclamen graecum alive, along with the easier C. hederifolum and C. coum. Species tulips, like Tulipa cretica have also performed well. Galanthus elwesii var. monostictus is happy so far, toward the bottom of a slope, where the bulbs get some extra moisture.
Corydalis don’t love the south, but a couple do well here. Corydalis leucanthemum ‘Silver Spectre’ has variegated foliage and purple blossoms, going dormant in the summer heat. Corydalis heterocarpa is more of a beast, blooming all summer and seeding about, but who could resist those brown-throated blooms?
Ledebouria cooperi corpses have littered the landscape here in years past, but there is life for this plant in the crevice garden. Similarly, Barnardia japonica (syn. Scilla scilloides) is now a reliable performer here.
Ferns adapted to sunny conditions are handsome in the crevice garden. Astrolepis sinuata ‘Jo Levy’ and Cheilanthes lanosa do well here, along with Pyrrosia lingua and its crested cousin, P. lingua ‘Cristata’. Asplenium scolopendrium and Athyrium niponicum ‘Picta’ are good performers in the shady crevices. Selaginella braunii and S. uncinata soften the rocks in and around the seep.

Other Flowering Plants
Surprisingly, Dicentra eximia loves living in a sunny crevice garden in steamy Raleigh. As Tony Avent has demonstrated, this plant is not really an ephemeral shade lover, though many of us have grown it that way. Mine blooms from March until November with just a few welcome seedlings. In the shady crevice, Viola labradorica spreads slowly but surely.
Aethionema species seed around just enough, blooming reliably, and their glaucous foliage playing well with other plants, especially the silvery leaved dianthus cultivars.
All the dianthus trialed so far have performed well. I’ve been especially enjoying Dianthus henteri and hybrids Dianthus ‘Cherry Charm’, ‘Kahori’, and ‘Mountain Frost Pink Twinkle’. In the near future, I hope to try some of the very tight forms, like D. ‘Minimounds’, which grows so successfully in the Juniper Level crevice.
Hybrid phlox from the Paparazzi and Bedazzled series do nicely, with handsome foliage and a long blooming period. Globularia species also do well here – so far, I have Globularia cordifolia and G. valentina, both grown from NARGS Seedex seed, the latter in bloom now in the first week of April. Ipomopsis aggregata subsp. candida, a white form of scarlet gilia is neat and fresh, with long-lasting flowers. Geranium species are easy and flower on and off throughout the summer in the crevice, as does Campanula portenschlagiana. Variegated Ajuga incisa ‘Bikun’ blooms well in the shady crevice, unlike its counterparts in the garden beds.

Lessons learned
On the whole, my North Carolina crevice garden has been an absolute joy: it’s a place to play and experiment with all kinds of plants that had previously failed for me in the garden and even in troughs. I have made some big mistakes, like not removing every single pine tree in the vicinity, resulting in pine debris in the crevice garden pretty much year-round. Plant choices in the seep, particularly Sarracenia species and Dionaea muscipula, didn’t work with the limited sunlight. I’ve started replacing those plantings with gentiana and primula cultivars, like Primula x kewensis.
After realizing that rock gardening in Raleigh was possible, finding the right person to build the garden was the most important next step. I’m grateful to Tony Avent for the inspiration, the plant knowledge he shared, and for the opportunity to volunteer. I am in awe of Jeremy Schmidt’s skill and his beautiful, thoughtful design and build.
I look forward to many happy years of horticultural adventure here, at the top of my driveway. Plant labels may become tombstones, but there are also thrilling successes along the way. That is especially wonderful and precious to me now, in the spring of 2020, at a time when we are all confined to home.