Ground Covers for Rhododendrons
By Jeannette Grossman
The rhododendron enthusiast who spaces his plants to allow for future growth often wonders what to do about the bare ground between and in front of his plants. I would like to relate to readers how we have worked out this problem in our own gardens.
When rhododendrons are very small and widely spaced, filler shrubs may be used to be removed later. We have used hydrangeas for this purpose since they do well in partial shade. But most areas are planted to the lower growing plants. In choosing these low plants, I felt they should have several characteristics. Suitability was of prime importance. These plants must be able to grow in acid soil and partial shade and fit into the picture in regards to foliage and flower. Invasive plants, though they would quickly cover the bare areas, would steal food and moisture, so they were ruled out.
In one portion of our garden, both sides of a path leading from lawn to woodland are planted with R. 'Bow Bells', R. 'Moonstone' and R. 'Humming Bird'. These slow growing dwarfs are inter-planted with the biennial Forget-me-not, myosotis . The modest blue flowers provide pleasing colour contrast and they do not demand the limelight. Their low growth does not smother the rhododendrons and any seedlings coming up too close is easily pulled out. Pansies seemed too robust for this area and the delicate creams and pinks of the rhododendron blooms would appear faded among pansies of a strong yellow colour.
In a border planted to the R. campylocarpum , hybrids with their creamy yellow and apricot trusses, we have used the Viola, Pride of Victoria as an edging plant. The soft lavender blue flowers make a pleasing colour combination with the rhododendron blooms. Here too is suitability to growing conditions, and a lack of invasive traits. A long blooming season and good foliage might be added as other good qualities which this Viola possesses. The late blooming Lillium formosanum is also included in this planting, providing bloom in September.
Much thought has been given to the ground covers in the woodland. A portion of these woods are planted to the red hybrids R. 'Langley Park', R. 'Earl of Athlone', 'R. C. B. Van Ness' and R. 'David'. Some species are also included. The native ground cover beneath the firs, pseudo dogwoods and vine maples is Vancouveria , the low Oregon Grape Mahonia Nervosa , Asarum or wild ginger and ferns. It seemed best to grub out the Vancouveria from the rhododendron area, because of its invasive root system. Some of the Oregon Grape was left, also the ferns and Asarum . The wild ginger is an ideal plant for woodland. The rather bold, heart shaped leaves are evergreen, it is low and creeping and has a well behaved root system. Gaultheria procumbens , the wintergreen of the eastern states has been planted in place of the Vancouveria . In shade and a peaty soil it makes mats of evergreen foliage and bears small white flowers followed by red berries.
Other good plants for ground cover might include Vaccinium vitisidaea , a stoloniferous evergreen from the arctic, Gaultheria miqueliana , Galax aphylla and the beautiful Shortia uniflora , the last two belonging to the genus Diapensiaceae .
Though primulas are not usually regarded as ground cover plants, they can be planted among the larger rhododendrons providing they receive some sun. Try P. pulverulenta , Bartley strain, a lovely Asiatic, but do not allow to close to the scarlet red rhododendrons if you would avoid a clash of colors. Mid-May to early June is its blooming period.
Bulbs which naturalize in woodlands and seem to fit, are the various Erythroniums, Snowdrops, Crocus, Alliums, and Trilliums. It is best to plant these in drifts, as hard lines and straight rows are not pleasing, especially in the woodland. Light shade is recommended for these minor bulbs as they must have some sun to ripen their foliage.
The many small leaved species rhododendrons must not be overlooked, though I have found they require rather more sun than our woodland provides if they are to keep their dwarf, compact habits. Single plants of some of these dwarf species are now planted on the sunny edges of the woodland in what we call our trial ground. Favorites will be selected and planted here in groups of three to five plants of one variety. This massed planting will probably include R. scintillans and R. chryseum in the Lapponicum series. R. racemosum , Forrest's form, R. oleifolium and R. ciliatum are being tried.
This by no means exhausts the subject of good ground cover. Many more are listed in the catalogues of specialists and still more may be found by visiting the nurseries.