Cambridge University Botanics Mountain Plants Diary
This entry: August 2012, North American Beds by Helen Seal and Simon Wallis
This month we find that many of the European mountain plants have completed their flowering and there is more colour in the North American beds. These cover the west and south facing aspects of the large rocky mound, constructed by using the low-level doline that featured in last month’s diary.
This height was put to great advantage and a small waterfall splashes noisily down to a pool. To the delight of the visiting toddlers, the water then passes under the path and into the lake below. One of our odd jobs is to prod a bamboo cane, our homemade dyno-rod, through the under-path pipes after games of pooh-sticks have blocked them with fir cones.
We speculate if the 1950s Superintendent Bob Younger had been reading Reginald Farer’s advice in “The English Rock Garden” before setting out on this large construction project. “The rock-garden should not be near a wall, a border, a formal path, a house: or within sight of any such regular and artificial construction.” However, contrary to instruction, it is near to what are now “trees and big bushes”, and these screen it effectively from buildings, and provide an evergreen backdrop.
The waterfall and pool offer moist planting positions, rare in Cambridge, currently enjoyed by North American plants from lower elevations: the dramatic skunk cabbage, Lysichiton americanum and the rather too bountiful yellow Mimulus guttatus. In the foreground is an escapee from the European lakeside bed, Lychnis coronaria.
Far less invasive, and exotic is the red Mimulus cardinalis.
Ten different evening primrose species (Oenothera) have been planted in these beds over the years, and had they all survived there would be space for no other genus! This Oenothera speciosa thrives in the sunny stoney bed, the delicate fragility of the pink flowers belying its robust character.
The taller, more upright acid yellow Oenethera perennis grows prairie-style among the Erigeron formosissimus. This montane daisy came to the garden in 1957, from Vienna, although it hails from western North America.
A sharp-eyed observer can notice the soft, slender foliage of the bane of every rock gardener, Equisetum arvense. The rhizomes of this horsetail have safe haven under the rocks and rapidly replace the growths we weed away.
Another colourful combination is Allium cernuum and Californian poppy Eschscholzia californica. Many Allium species are a menace in the rock garden as their seeds and aerial bulblets are dispersed into the crevices and crannies, and no amount of prizing and pulling can dislodge them, as our selection of bent handforks attests. Thankfully A.cernuum spares us the bulblets. There are no photographs of the frequent name-changer Nothoscordum gracile as it has been de-flowered before those pesky bulblets scatter. Of course, the Eschscolzia seeds everywhere, but the seedlings are easy to remove.
Another vigourous seeder is the perennial Chilean Sisyrinchium striatum which has strayed from the South American bed. Its fan of linear leaves and pale yellow flowering spike have given variety of texture and form, but its post-flowering removal will provide planting places for the new North American plants we have raised from seed and which are growing on in our nursery. They will need to be strong plants to withstand our inevitable weeding of Sisyrinchium seedlings.
A welcome survivor which has competed for twenty years with the mat of high prairie plants is Triteleia laxa Syn. Brodiaea laxa, its contrasting blue flowers following on from the earlier Tradescantia species.
Again the keen observer will notice the backdrop of a Thymus species. Apparently this herb which is native to all temperate regions except North America, has escaped from gardens there just as it has in our rock garden. The weeder’s work is never done.
Helen Seal and Simon Wallis