The Rock Garden, Part 2: Planting Notes

Believe it or not, the Rock Garden, which now covers a good part of an acre of land on the Agricultural Campus of Dalhousie University had its early beginnings as one man's "little" retirement project. 

Dr Bernard Jackson had retired to Truro, Nova Scotia after spending 22 years as the Director of the Memorial University Botanical Garden in St. John's Newfoundland, when he was approached by the Agricultural College in Truro to create a new rock garden on their campus. 

With a modest budget of just five thousand dollars, Dr Jackson set about creating the garden you see today.

Basket of Gold, Aurinia saxatilis

As the Operational Manager for the grounds unit at the Agricultural Campus, Darwin Carr became the project's manager.  He made sure Dr Jackson had tools, materials and equipment, as well the labour for the daily construction and planting activities. Darwin oversaw the budget, as well as coordinated the efforts of the Friends of the Garden, the team of dedicated volunteers who help maintain the garden's specialist plant collections.

I owe Darwin Carr a huge debt of gratitude for providing me with all of the background information in this post, as well as assistance with identifying any of the unusual alpine plants. Thank you, Darwin!

In the limestone courtyard at the entrance to the Rock Garden, there are several large stone troughs that look like they must weigh a ton. Darwin tells me:

"The troughs are hand-cut sandstone. And yes, they are heavy! The big one at the entrance to the garden had to be carved right on location... We had a local stone mason/sculpture (Heather Lawson of Raspberry Stone) carve them out to provide room for soil and fragments of stone, then we planted them to create the miniature landscapes that you see now."

"Trough growing is a bit tricky in our east coast climate. The freeze/thaw cycles we generally get every winter tend to be hard on true alpines, but some things settle right in and love it."

Ice plant, Delosperma basuticum: is native to the mountains of South Africa. It forms a low cushion of succulent, green foliage and has starry yellow flowers. Full sun and excellent drainage are essential for this plant. Sandy or normal soils, with dry growing conditions, are best.  Height: 2-4 cm (1-2 inches), Spread: 15-20 cm (6-8 inches) USDA Zones: 5-9.

I asked Darwin to tell me a little bit about the choice of stone in the Rock Garden. 

"The choice of stone was a combination of factors. The natural bedrock in the area is a soft red sandstone, not very good for building rock gardens as it tends to melt away as it weathers... Luckily for us, there was a local rock quarry not far from Truro that has a surplus of red granite....They gave Bernard and me a tour and said we could have as much as we wanted. "

"Twelve loads of stone turned into fifteen as Bernard kept calling for "more rocks" as the construction moved forward. Over the next twelve years, we added many new features including a woodland walk, limestone courtyard with troughs, barrens and much more. We have plans to expand again next year."

With regard to the plantings Darwin informs me:

"We have been blessed to have formed the Nova Scotia Rock Garden Club with many members that are avid seed growers.  That's how half the plant material has come our way for the rock garden.  Many of the perennials plants are just not available in nursery trades. True alpines tend to be short-lived in our climate. So we tend to experiment with species. If we kill it, we try again until we find the right location. Our winters are hard on plants."

As you read through some of the plant profiles in this post, you will see that good drainage is a recurring notation. 

These are plants that hate to sit in damp earth, particularly in winter. But what constitutes good drainage? 

I asked Darwin Carr about the soil mix that was used to create the rock garden:

"The soil mix is equal parts topsoil from onsite (sandy loam), leaf mould/compost and sharp grit or pea stone. Then, once the plants are in and settled, we use course crushed granite as a mulch to cover the ground and protect the plant crowns from getting too wet.

Alpines require very good drainage as they are to survive our harsh maritime climate. That's the key to growing most alpines in landscape situations: drainage, drainage, drainage! Yes, I said it three times. Too many plants are put into regular garden soil and most don't survive one year. Many people think alpines are hard to grow or that you have to be a plant expert, but really it's just attention to the plant's needs."

The Rock Garden's collection of hardy cactus is a perfect example of the success you can have with plants when you address the issue of drainage properly. Darwin recounts:

"The hardy cactus bed is always of interest to visitors, especially when they start to bloom in early July. I've had many folks ask me if "we take them all in for the winter" or "how we glue on all those flowers". People are amazed that we can grow cacti in the landscape."

Cushion Spurge, Euphorbia Polychroma

Darwin: "Bernard decided that we would build a dry stream bed. It looks like water has been moving through the area, as is the case in all alpine streams which generally dry up in summer."

Cushion Spurge, Euphorbia Polychroma: prefers full sun and somewhat dry conditions. Normal or sandy soil is best. Trim Euphorbia Polychroma back in early summer to keep it neat and compact, but be careful to wear garden gloves as the milky-white sap the plant extrudes can be irritating to the skin. Height: 30-45 cm (12-18 inches), Spread: 45-60 cm (18-23 inches). USDA Zones: 3-9.

Evergreen Candytuft, Iberis sempervirens: Candytuft has glossy, evergreen foliage and white flowers that bloom for several weeks in spring. Prune lightly after flowering to keep it from getting leggy. Good drainage is essential and somewhat dry conditions are preferred. Candytuft is not easily divided.  Full sun. Height: 20-25 cm (8-10 inches), Spread: 30-90 cm (12-35 inches). USDA Zones: 3-9.

The two bridges in the garden were built by students studying woodworking.

Grey cranesbill, Geranium cinereum var. subcaulescens 'Splendens': has grey-green leaves and magenta flowers with a black centre. Trim plants lightly after they flower to encourage new flowers and a bushier plant. Full sun or light shade. Normal or sandy soil and somewhat dry growing conditions are best. Height: 10-15 cm (4-6 inches), Spread: 25-30 cm (10-12 inches). USDA Zones: 4-9.

Dwarf Renard Cranesbill, Geranium renardii: is a great choice for sunny, well-drained sites like the Rock Garden. It has textured, grey-green foliage and white flowers veined with mauve in late spring. Full sun or part shade. Normal or sandy soil and somewhat dry growing conditions are best for this geranium. Height: 15-20 cm (6-8 inches), Spread: 20-30 cm (8-12 inches). USDA Zones: 4-9.

Bloody Cranesbill, Geranium sanguineum var. lancastriense : has green foliage and pretty pink flowers in late spring. Unlike the previous two geraniums, this one tolerates a variety of soil and growing conditions.  Full sun to light shade. It is also a bit taller than the previous Cranesbill geraniums: Height: 30-40 cm (12-16 inches), Spread: 45-60 cm (18-23 inches). USDA Zones: 3-9.

A Pasque flower gone to seed.

This is a plant for which I found many common names: Rattleweed, Cow Bell, Bladder Campion or Catchfly.

Bladder Campion, Silene uniflora: has a low cushion of grey-green leaves and white flowers in late spring. It can be grown in a range of soil types and tolerates both dry and moist conditions. Full sun to light shade. Height: 5-10 cm (2-4 inches), Spread: 20-30 cm (8-12 inches). USDA Zones: 3-9.

The next plant makes a home in a tiny crevice in the rock.

Dwarf Snapdragon, Chaenorhinum origanifolium: has a purple flower with a white throat. It likes full sun or light shade. It has average water requirements, but like most of the plants in this blog post, it needs good drainage. Height: 5-15 cm (4-6 inches), Spread: 15-20 cm (6-8 inches). USDA Zones 7a-9b.

Purple Columbine

Bellflower, Campanula chamissonis: has compact green leaves which grow not more than two to six inches high. Light purple, bell-shaped flowers with a white throat appear in mid-spring. Again, good drainage is essential. This campanula is not invasive. Full sun. Height: 5-15 cm ( 2-6 inches), Spread: 15-20 cm (6-8 inches). USDA Zones 4-7.

Welsh Poppy, Meconopsis cambrica: Prefers moist, well-drained soil and part to full shade. Note: It is a very good self-seeder given the right conditions. Height: 30-45 cm, Spread: 45-60 cm. USDA Zone: 3-11.

The seed pod sculpture is the work of stonemason Heather Lawson.

I end with this sculpture and the hope that this beautiful Rock Garden in Nova Scotia may plant a seed of inspiration. Here's a link to Part 3 in the series (Missed the first post? Here's a link back to Part 1)