The Rock Garden and Rhododendrons
Reuben Hatch, Vancouver, WA
Reprinted from American Rock Garden Society newsletter
Rhododendrons can be very useful subjects in the rock garden. They can be mixed with herbaceous plantings to provide contrast, combined with other small woody plants or used by themselves in an alpine type grouping. The latter if carefully planned can provide a very effective tapestry of form, and of flower and foliage color. The choice of rhododendrons considering species and hybrids is quite extensive. (Rhododendrons in this discussion will be limited to the lepidote or scaly leafed group as contrasted with the elepidote or the azalea groups.) In terms of plant size one can choose from truly elfin varieties reaching only two inches high by eight inches across after ten years, through the more typical globe shaped varieties of two feet by two feet, up to the larger upright varieties are more suitable for use along the borders. Rhododendrons can be transplanted easily, which simplifies their placement. Most of the lepidote rhododendrons bloom at an early age. Choice of flower color is broad with blooming periods ranging from early February through June. A second flush of color in late summer can be counted on with some varieties. Foliage color is usually as varied with hues through the range of green with tints of red, bronze, grey, blue, and gold. The winter brings on a darkening of foliage in many varieties to hues of chocolate and gun-metal grey. A bonus feature of some varieties is the fragrance of the foliage which when brushed against or crushed produces a pleasantly pungent odor.
Rhododendrons are relatively easy to cultivate. Some suggestions for their care would include choosing a planting site to insure good air drainage - an incline or raised bed - providing plenty of organic material around the root ball, fertilizing sparingly and removing all spent flowers after blooming. Most varieties will perform well in open exposure if sufficient watering can be provided, interplanting with sun-loving woody plants such as potentilla seems to reduce the stress from summer sun.
A brief description of a few varieties which have proved interesting and reliable in our garden follows. These plants are all slower growers reaching more or less two feet by two feet after ten years.
'Pink Snowflakes' This hybrid of racemosum x moupinense brings out the best qualities of both parents. The plant makes a shiny leaved mound accented through fall and winter by flower buds of bright rose color. The flowers which open late winter are white suffused pink with red specks. The new foliage, a shiny bronze, is like a second blooming.
'Small Gem' Another hybrid of American origin also brings out the best of its parentage which is pemakoense x leucaspis. The plant forms a dense mound of deep green. It covers itself in April with white flowers accented by chocolate colored anthers.
lepidotum "Reuthe's Purple" A.M. This small leafed multi-branched plant contributes in mid-season an abundant display of clear lavender purple flowers. Not satisfied, it regularly blooms again in the fall.
glaucophyllum var. album. This variety was introduced from a recent plant expedition in Nepal. Unlike other forms of glaucophyllum, this plant is quite compact making a dense mound less than one foot after seven years. The plant produces clear white flowers in early mid-season.
calostrotum 'Gigha' F.C.C. This clone which originated in a Scottish garden is also a slow grower. The foliage is an attractive blue grey accented by beige coloring under the leaf. There are many forms of calostrotum in circulation but none to my knowledge that compares in flower quality to the bright wine-crimson produced by the Gigha clone.
russatum King and Patton. Of olive grey foliage and a bit open in habit this plant's claim to fame rests with its bright royal purple flowers. A marvelous contrast plant when in bloom.
'Curlew' (ludlowii x fletcherianum). This hybrid is the product of Peter Cox of Scotland. Cox has produced so many worthwhile hybrids, mostly rock garden type, that it is difficult to narrow one's choice. 'Curlew' is certainly one of the better small hybrids available. The plant makes a mound of deep green shiny foliage covering itself with bright yellow flowers in early spring.
ludlowii x lutescens. This, another Cox hybrid using ludlowii, (ludlowii itself is a difficult and virtually useless plant) produces large clear yellow flowers brightly punctuated with red spotting. The new foliage through the growing season is tinted reddish bronze.
The list could go on and on (heaven forbid!). Suffice it to say that there are many varieties to select from.