“The purple petals, fallen in the pool,
Make the black water, with their beauty gay,
Here might the red-bird come, his plumes to cool,
And court the flower that cheapens his array,
Rhodora, if the sages ask thee why
This charm is wasted on earth and sky.
Tell them, dear, that if eyes were made for seeing,
Then beauty is its own excuse for being.”
These lines about a rhododendron species are from Ralph Waldo Emerson’s well-known poem, “Rhodora,” which refers to the deciduous American species, Rhododendron canadense, with glaucous foliage and many spidery, orchid-pink flowers.
This quotation sets the proper tone for a study of the rhododendron species. We examine the beautiful woodsy plants native to cool and peaceful forests and the rugged plants that brave high mountains’ strong winds and chilling temperatures.
And we find that, wherever they grow and flower, they bring delight to the eye and a lift to the spirit. This they will do in the home garden and their native habitats!
Nature Of The Rhododendron Species
Species are a basic concept in rhododendrons—the beginning point. They have unique characteristics that few, if any, of the hybrids retain.
Yet far too many of our rhododendron growers allow their enthusiasm for the spectacular modern hybrids to monopolize their interest in the genus. They ignore the subtle charm and beauty, the refined qualities, of certain species and their varieties.
The physical plant—the rhododendron that one sees—is only a part of the story.
The beauty that appeals to the eye, the fragrance that pleases the sense of smell, and the texture of the leaves that affect the sense of touch stimulate the plantsman’s mind and spirit.
But they must be coupled with a study of the inherent characteristics of a given species and its varieties to ensure a full understanding and appreciation of that particular plant.
Rhododendron Arborescens Varieties
Here in the Tacoma area, we know 3 varieties of Rhododendron arborescens:
- One with white flowers which is similar to the type—an upright, open plant
- Another that is different in color—a magnificent, pink-flowered sort
- Richardsoni is native to high altitudes where wind and weather conditions have produced a low-growing, compact, mounded plant form.
However, all 3 varieties have a group of common characteristics peculiar to all plants that make up the arborescens species.
The mental concept is the determining factor in the grouping or classifying of this particular species.
In their origin, species are native to certain localities in the Northern Hemisphere, very few being found below the equator. (China is the great species center.)
Members of a single species group may be scattered over several areas, and, of course, the environment may modify the characteristics of the species. These modifications are known as varieties.
The gardener should remember that species came into being slowly, and their struggle for survival was a part of the violent upheavals, the stresses and strains of natural adjustment that made our world what it is today—that made the rhododendron species what they are today.
The perceptive plantsman—the true rhododendron lover—sees all of this in the poise and character of the species in his garden.
Adaptiveness, a prime value of this group of plants, has its roots deep in the origin of the species.
“Must” Growing Requirements
Gardeners in any locality who plan to grow rhododendrons should attempt to duplicate the growing conditions of their native habitat.
Proper Soil Conditions
Proper soil is important. Rhododendron roots are fibrous and excellent, and husky root systems will not develop in hard soils that tend to pack and become waterlogged.
Here are the tips to follow:
- The soil must be conditioned unless the planting is done in natural peat.
- Holes should be dug much larger and deeper than needed and should be filled in with “made soil,” loose, friable, and acid.
- Peat moss or leaf mold and woods soil will serve the purpose, and it should be mixed with 50% percent of good rich soil.
- In planting, the top of the root ball should be kept right at the soil level, with not more than 1″ inch covering. Since the top roots are for aeration, deep planting results in poor growth, sometimes in the loss of plants.
- A mulch of oak or maple leaves will add acidity to the soil, conserve moisture, and keep the root area cool in summer.
- The soil should have a pH factor of between 4.5 and 5.5. A higher factor means a tendency toward alkalinity, resulting in poor development, and a lower reading means too much acidity, which is often dangerous.
- Chemicals for inducing acidity should be used sparingly and carefully. Spread them evenly and thinly, watering in thoroughly.
Commercial rhododendron fertilizers made up of an acid formula are fine in localities where the soil is alkaline. They will usually solve the acidity problem in such situations.
In localities such as we have in western Oregon and Washington, where the soil is naturally and continuously acid, no acidity treatment is advisable, for it can be harmful.
Annual Feeding For Rhododendrons
Rhododendrons are good feeders. Ordinary barnyard fertilizer of the bovine variety is fine for an annual feeding.
Epsom salts in solution (one cup of crystals to a gallon of water) can be applied over the feeding area of the plants several times during the season.
This adds magnesium which will assist in the production of chlorophyll and prevent the development of chlorosis indicated by a yellowing of the leaves.
Cottonseed meal, valuable plant food, and a ready source of nitrogen will assist in the growth of beautiful foliage. It also contains appreciable amounts of phosphorus and potassium.
All of these materials can be used simultaneously, and no damage will result if reasonable quantities are applied.
The acid commercial rhododendron fertilizer should be beneficial where the soil is alkaline.
Wind Protection
Wind protection is important. Drying winds, either hot or cold, are always damaging.
Advantages should be taken of the shelter provided by buildings, such as:
- Fences
- Walls
- Hedges of trees and shrubs
Ideal Temperature And Watering
The soil of a rhododendron planting should be damp at all times. It should never be dry, especially in summer.
In sections where the temperatures and sun are severe, watering must be heavy to temper the heat and compensate for the lack of moisture in the air.
Low humidity is not to the liking of rhododendrons. Here in the Puget Sound country, we have high humidity at all times, and the temperatures seldom go above 85° degrees Fahrenheit, yet heavy summer watering is necessary.
Proper Climate Protection
Most rhododendrons should be protected from too much sun.
In hot localities, the plants must be adequately shielded in front of the midday sun by trees or lath shelter.
In cold climates where the ground is frozen for long periods, the plants must be protected from rapid thawing by warm winter sunshine while their roots remain frozen and inactive in the cold earth.
Rhododendron Species For Unfavorable Climates
Those who garden in the most severe localities where there are extremes of heat and cold will need to exercise great care in species selection.
It is never wise to attempt to grow plants of doubtful hardiness in such situations.
Many of the deciduous azaleas are hardy and adaptable, and many are first-class rhododendrons.
- Rhododendron roseum has many clear pink flowers and a pleasing spicy fragrance. This is a prime rhododendron, judged by any standards. A large specimen won first place as the best plant of a species in the 1953 Tacoma rhododendron show in competition with the best of the tender species. Rhododendron roseum is a neglected beauty.
- Rhododendron canadense is entirely as good as Emerson’s poem indicates, and it is a real “toughy.”
- Rhododendron albrechti, a beautiful species with delicate wide-open flowers of deep pink color, has real quality.
- Rhododendron calendulaceum is highly colorful with various shades and blends of orange, red, and yellow.
- Rhododendron nudiflorum has flowers that vary from white to pink.
- Rhododendron arborescens has been described above.
- Rhododendron Schlippenbachi is a charming species with wide-open flowers from white to delicate pink.
- Rhododendron maximum is a white-flowered, large-growing evergreen species.
- Rhododendron Smirnowi makes a beautiful evergreen plant, and the orchid-pink flowers are attractive in better varieties.
- Rhododendron carolinianum is a grand evergreen species that can be grown well as far north as Massachusetts.
Properly used, this group of species would make up a first-class rhododendron garden. Most of them are top quality plants in their class.
Rhododendron Species For The Small Garden
The small gardener is also fortunate since many good species are available.
- The tiny lovely Rhododendron cremastrum, with Tom Thumb flowers of an off shade of pink.
- The sturdy little stoloniferous Rhododendron pemakoense with orchid colored flowers.
- The dwarf variety of Rhododendron racemosum with lacy, foamy flowers.
- The creeper Rhododendron radicans with baby purplish-blue flowers are only a beginning of the treasures the plantsman who gardens in a restricted area can grow.
He can grow rhododendrons (lots of them) of top quality.
Rhododendron Species For Favorable Climates
Gardeners who grow their plants in a favored land, such as the Rhododendron Belt in Western Oregon, Washington, and Northern California, and those who live in climates only moderately severe—are fortunate people who are not restricted in their choice of species material.
Yet most of them fail to realize their potential blessings. This is primarily because rhododendron people have not publicized and spotlighted the available species.
A sizable woodland garden, either natural or simulated, can be transformed into a virtual fairyland of plant wonders if an intelligent selection of species is used in natural situations and the environment.
With such a wealth of species material to choose from, the gardener can use all of the sensitive awareness, the sympathetic understanding, and the ability to create real beauty that he can muster.
However, let it also be said that species can be used effectively in the more formal garden or any landscaping the plantsman wishes.
He may want to grow only a few of these plants with other types of garden material.
Whatever his desire, there are species to suit him.
Our native evergreen species, Rhododendron carolinianum, has slightly pinkish flowers and an elegant growth habit.
Several enthusiasts in western Washington grow it along with British hybrids and oriental species, and it holds its beauty.
It turns up in our West Coast shows regularly and wins its share of the prizes, often over aristocrats that are much better known.
The album variety is a perfect jewel of a plant, with pure white flowers.
An excellent specimen won the gold medal for the Best Plant of a Species in the show at Tacoma in 1952.
An excellent plant of Rhododendron neriflorum placed second to it, and a wonderful color form of Rhododendron dichroanthum placed third.
Yet only an isolated few horticulturists know and grow this peerless shrub.
The noble reds and yellows of the deciduous Rhododendron Bakeri are scarcely known, but those of us who grow it in the West value it highly.
Rhododendron eriogynum is a late-flowering species with bold, flashing red flowers.
Rhododendron Fortunei has large trusses of white flowers that are slightly fragrant. It has considerable hardiness.
Rhododendron decorum belongs to the same series as Rhododendron Fortunei, but it has a distinctive beauty.
Rhododendron vernicosum, also in this family, has pink flowers.
There are many other fine species, and they come in a considerable range of sizes.
Seasonal Flowering In Mild Climate Gardens
Early in the new year, here in the west, the precocious species cheer the gardener on dark winter days with their bright flowers.
Rhododendron mucronulatum will open orchid-pink flowers in a lovely show in January.
Rhododendron dauricurn will duplicate this in February and have Rhododendron moupinense and Rhododendron leucaspis, both white-flowered.
The impressive Rhododendron sutchuenense, species with light pink flowers and a dark blotch, will often begin flowering in late February.
March and April bring a host of species into flower. May and June are crowded with the largest group to flower in the season.
July will bring the flashy, native deciduous azalea into flower, Rhododendron prunifolium, a magnificent rhododendron.
Some varieties of Rhododendron occidentale will flower in July also.
Rhododendron discolor and Rhododendron diaprepes have white flowers, large plants, and fine July-flowering sorts.
In August, Rhododendron auriculatum, the treelike, white-flowered, and slightly scented species will have the latest flowering varieties of Rhododendron occidentale.