Thank you AGS for suggesting a blog from the Alpine and Woodland team at Cambridge University Botanic Garden. We are delighted to share this special area of the Garden with you.

Our Limestone Rock Garden is planted out geographically by continent.  This first blog focuses on an area of the European section of the Limestone Rock Garden that specializes in the Balkan flora. Here it is in mid-June.

It’s a curious area because it has a round, sunken hole in the middle of it.  It’s called a doline and is a mini representation of a collapsed underground cave in a karst limestone area.

When this Rock Garden was constructed in the mid 1950s, a lower area was dug out to house the tripod, block and tackle used to hoist the rocks to the top of the waterfall. Upon completion, to disguise the remaining hole, it was lined with rock walls to form vertical planting niches facing every aspect.

The curved oak bench is a new addition, paid for by the ever-generous Friends of the Garden and made to measure by the University’s own Estates Management carpenters.

We know that several of the early plantings still survive thanks to the recording requirements of a botanic garden. Every plant is given an identifying number to which we attach all sorts of data. These electric blue cascading Moltkia suffruticosa were donated by Wisley in 1953 and grow equally well on the west and south facing doline walls.

Moltkia used to be included in the genus Lithospermum and like many plants in the Boraginaceae family are hairy and have tubular flowers in shades of blue.

The 1950 gardeners were more relaxed about their geography than we are now: this Moltkia in the wild grows in the mountains of Northern Italy rather than the Balkans! But another Moltkia does originate from the Balkans - Moltkia patraea- a smaller, more upright plant with shorter, more glaucous leaves. We thought we had lost it, and it was only when preparing this blog that we refound it.

Also persisting with minimal attention are Rosa pendulina, a low, suckering species of rose, with deep pink, single flowers,

and Geranium dalmaticum, now a mass of delicate pink flowers,  which is threaing its way through the gaps in the rocks.

The records show that this Geranium came into the garden in 1957 from Valerie Finnis , the renowned plantswomen.

It is a dense mat and isn’t one of those nuisance seeding geraniums which stray away from their home bed. Geranium versicolor does wander, but is easily recognized by its white flowers with gothic tracery of purple, and basal blotched leaves.

We botanic gardeners sometimes behave rather oddly: we wait until our mountain plants are in flower, so we are sure of their identity, and then we weed them out, just when they are at their most attractive! When the 1950s botanists organized the Rock Garden into beds to represent the flora of the different mountainous areas of the world (phyto-geographic planting) they provided weeding work for generations of gardeners as we restrict plants to their areas of wild distribution.

Not many of the 1950s plantings have survived of course: lack of moisture must have killed off many in the vertical walls. The built-in sprinkler irrigation system was quickly coated with limescale deposits from our alkaline water, and stopped working a couple of decades ago. The Garden now has a policy of only watering to establish plants, after which they must take their chances with the random distribution of an average 560mm of rain per year.

On the south facing top of the bed, we are trialling Achillea chrysocoma ‘Grandiflora’ recently donated from the Dell Garden at Bressingham by Curator Jaime Blake.

It will have to defend its place from the expanding adjacent patch of Helianthemum. We will imitate grazing herbivores and remove at least half the growth of this after the petals fall.

This selective cutting back and weeding are our main maintenance tasks, with occasional propagation and mulching with grit. We hope the Rock Garden inspires some of our visitors to grow these plants in their own gardens: after all, the plants do not receive any special horticultural treatment like irrigation, feeding, and weather protection.  We just provide an open site with good drainage, make thoughtful use of aspect and planting niches, and are mindful of the vigour of the competition from neighbouring plants.

Helen Seal and Simon Wallis

June 2012