Companion Plants for Rhododendrons
C. Gordon Tyrrell, Dir. of Winterthur Gardens
This is the age of plant societies, and if you count them up there are over sixty-five different plant societies in the country. Most of their members have blinkers on to any plants other than their particular interest, and are not always aware what other plants there are to be enjoyed by all. This goes for this society too. This was brought home to me at the International Congress held in Portland a few years ago. On a trip to rhododendron nurseries and gardens, most everyone rushed off to look at rhododendrons exclusively. Others of us were enjoying other plants as well and we were very happy that our escorts for the day soon sensed this, and took us to visit other gardens.
I want to give you some idea of particular plantings at Winterthur. You may be sure these will include rhododendrons and azaleas because they are what Winterthur is famous for. Many of you must be making use of plants other than rhododendrons and azaleas, and I hope those of you who are not will want to get involved with other plant material.
At the entrance to the Azalea Woods is a group of Kurume azaleas in three or four shades of pink and salmon, with a complete under-planting of Scilla campanulata, the bluebell. What a subtle color combination. Within the woods is a beautiful spring flower Anemone apennina, which is easily grown, all it needs is a woodsy area with a little sunlight to give it a chance to grow. Our patch has been at Winterthur for many, many years and had spread very little until we cleaned out some of the spice bush and other things, to give a little more light. Now it is spreading all over. Try this small bulb and get years of pleasure from it.
Wherever possible in our plantings native material is used such as Anemonella thalictroides (the rue-anemone) a dear little plant that is so handsome and it can be used with effect in a woodsy area. Phlox divaricata and Claytonia virginica can also be used for a lovely effect. Most of us who are growing rhododendrons will have some of them in partial shade of a woody area or in shade of trees, and this is the ideal setting. Some plantings are out in full sun, and these have different treatments.
There is also a good planting of Trillium grandiflorum. This again was given a large area when it was put in years ago and is doing very well. We know this because it is seeding itself in other areas beyond the original patch. Other trilliums used are T. cernnuum, T. erectum, T. nivale, and T. sessile, but the grandiflorum is the great sea of white and will last in bloom as long as three weeks.
For your enjoyment, you do not have to have large plantings, but try a few Scilla sibirica, the very early spring plant, one of the first signs of spring. They can be grouped under rhododendrons and azaleas to good effect, the best variety being 'Spring Beauty'. Other small bulbs are chionodoxa, snowdrops, and muscari, which can be planted in drifts, or around individual plants.
Ferns are not to be spurned in any garden, from the small Lady Fern, Athyrium filix-femina to the big Ostrich Fern, Pteretis nodulosa. Some others worth recommending are the varieties Asplenium (the Spleenworts) and Dryopteris (the Woodfern). Seeing the fiddles opening up in early spring with their soft green color, so delicate so dainty, make them well worth a place in any garden.
Along a woodsy path can be found a planting which is perfectly natural. A beautiful setting with the mayapple. followed later on with its fruits. Of course the jack-in-the-pulpits, which we can have in all sorts of forms, are delightful. None of the native plants should be left out in preference to cultivated material. The two can go hand in hand, one with the other. Try Polemonium reptans (Jacobs-Ladder) and Mertensia virginica (Virginia bluebell) with Claytonia virginica (Spring beauty) and the many native violets.
The English primrose, Primula vulgaris is a very happy plant in the woodsy area of the garden. What started off as an experiment with a few patches raised from seed, had proved so successful, that the last two or three years we have raised thousands of seedlings to be put out. With the acreage at hand we can put out groups of maybe fifty or a hundred plants. A planting of a dozen could still be enjoyed, along with Primula ver is (the cowslip).
Another experiment that was tried a few years ago was the use of blue aquilegia, which happened to be left over from use in a formal area. These have now seeded themselves and are a color contrast to the pink azaleas and rhododendrons in the area. Even now any plants left over are put in the woods along with foxglove.
We are planting lilies for the June visitor, using Lilium 'Gay Lights' and Lilium 'Paisley Gem', among the azaleas and rhododendrons in the woods, inserting them with a mattock in the open areas. A couple of hundred bulbs were planted originally, but since many more have been put in, as they gave such a good effect. Do not be disappointed if there is not a good showing the first year, as they are not planted in a bed they take a year to settle down.
One of the early blooming rhododendrons is R. mucronulatum, with its lovely pale mauve flowers. It is used at Winterthur with corylopsis, in three varieties C. spicata, C. platypetala, and C. sinens is as accents. All usually bloom around the 15th of April.
Bergenia cordifolia helps pick up the same mauve color and as a plant is very useful because after flowering there is still leaf texture, which persists all through the summer.
We have found that the hellebores (Lenten Roses) do very well for us in the Corylopsis/Mucronulatum area. By the use of H. orientalis, H. atrorubens, and H. 'Delicatissima' we pick up and accent the colors of the basic plant material.
It isn't for the flowering season alone that we plant azaleas and rhododendrons, but for the color and texture of the foliage in the fall, which give an extra dividend. This is very true of the R. mucronulatum and the corylopsis planting, as the russet and yellow color combination in the fall is very pleasing.
Another plant that lends itself for early spring with R. mucronulatum is Prinsepia sinens is (Cherry Prinsepia). Opening with very dainty foliage of chartreuse green with small yellow flowers, which are almost insignificant, but can compliment the color combination even though the main use is for that very soft green foliage.
At the edge of a path planted with Rhododendron balsaminiflorum we find Camassia leichtlini atrocoerulea (Atlantic Camass) growing side by side. This is quite an attractive bulb and readily available even though not too well known. After all the purpose of this talk is to acquaint you with some of the better things that you ought to know about.
Syringa persica (the Persian lilac) can be used so well with the azaleas of the same color and is a small enough plant for the average garden. We use it with Kurume azaleas of the same lilac color.
There are many Prunus to pick up the color accents of our azaleas. In the early spring with the pink forms of R. mucronulatum use P. 'Accolade', which opens up a pink and turns to a flush white as it fades. Prunus tomentosum is a smaller plant, only 2½-3 feet, but how attractive and how welcome as an addition to any azaleas we might have in the area. Another Prunus we highly recommend is P. 'Hally Jolivette'. This was originated at the Arnold Arboretum and is a small tree, useful for the home planting.
In the Ghent and mollis azalea planting, use is again made of Scilla canipanulata (Bluebells) with tall plants of Viburnum in the background. Whether they be V. burkwoodi, V. carlcephalum, V. juddi, or V. macrocephalum, all do such a good job as background material.
A small tree that should be recommended is Chionanthus virginica, the Fringe Tree. This is in bloom in mid May with its soft chartreuse/cream colored flowers. Planted with the Fringe tree are R. 'Orison', R. 'Killarney', R. 'Memento', and R. 'Sarabande' either in off white or cream, or with flecks of pink color. Used to compliment these is Cotoneaster hupehensis, a large shrubby form, 6-7 feet all and as a ground planting C. horizontalis.
Fothergilla is another shrub worthy of mentioning, either F. major or F. monticola, not only for bloom in May, with a bottle brush of white, but for its foliage in the fall, with its dark reds and almost purples, gives it an extra quality at that time.
Kalmia latifolia is a plant that does well in the partial shade or full sun. Do you know the newer one K. l. 'Red Bud', which I think was originated in California?
The Enkianthus perulatus and Enkianthus campanulatus both companion plants, are also very good for fall color. All of these like the same type of soil required by rhododendrons and azaleas, so there is no more trouble involved preparing for them than for our 'Society' plants, so why not widen our plant horizons.
In May our color scheme of mauve and yellow, in April, is again picked up with Rhododendron 'Conestoga' (R. carolinianum x R. racemosum) or Rhododendron 'Conewago' (R. carolinianum x R. mucronulatum) with Ribes aureum. These go very well together and as an under planting hundreds of Triteleia multiflora or Milla uniflora are used to add a touch of blue for a stunning effect.
The use of companion plants with a particular color scheme in mind is being stressed at Winterthur. So with Cercis canadens is (Red Bud) is planted R. reticulatum, R. arnoldiana, and R. poukhanense (Gable's special) as well as other varieties in the same shades of color, with daffodils to give accent.
Paidownia tomentosa lends itself to an underplanting of lavender and white by the use of R. 'Catteya' and R. 'Treasure', supplemented by Buddleia alternifolia a butterfly-bush with drooping branches.
For azaleas and rhododendrons out in the sun try planting pieris; either Pieris floribunda, with the flowers in the upright habit or the well known Pieris japonica, with its tassels of white hanging down. Newer ones are on the market, such as Pieris 'Flamingo', which has beautiful red flowers and lovely foliage in the fall color, Pieris 'Dorothy Wyckoff' with creamy white flowers and spectacular fall foliage. A plant well worth space in anyone's garden is Pieris 'Forest Flame', a hybrid between P. forrestii and P. japonica, and is something we easterners can grow, while P. forrestii we leave for our western friends.
A fairly large tree of Aesculus carnea brioti (Horse-chestnut) with its pink flowers in May is used as a background for the later blooming Glenn Dale azaleas in shades of the same color. Among those used are R. 'Coralie', 'R. 'Alight', R. 'Buccaneer', R. 'Beacon', R. 'Stunner', and R. 'Scout' to name just a few. A smaller aesculus to recommend is Aesculus spendens, which will give the same effect color wise, and is more appropriate for a home garden. It also has quite attractive fruit, which looks like small pears when fully formed.
The dogwoods are familiar to all of us; I'm sure we all grow them. Cornus nuttalli for those on the west coast and Cornus florida for those of us on the east coast, one of the better varieties being Cornus Florida 'White Cloud'. For those who want June blooming there is Cornus kousa to use. Almost as useful in bloom as the dogwood is Viburnum tomentosum. Its flowers born in flat heads along the branches in the same fashion as dogwood blooms, but later, at a time when background plants are needed. The red fruit in the fall is much more showy than the native dogwood.
This gives some idea of the plant material in use at Winterthur to supplement and complement the azaleas and rhododendrons that are planted by the hundreds.