These lines below about a rhododendron plant 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.
“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.”
This quotation sets the proper tone for a study of the rhododendron species. We’ll examine the beautiful woodsy plants, native to cool and peaceful forests.
Rugged plants braving the strong winds and chilling temperatures of high mountains.
We’ll discover 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 as well as in their native habitats!
Nature Of A Rhododendron Plant Species
Species are a basic concept in genus rhododendrons – the beginning point. They have unique characteristics all their own 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
- The texture of the leaves that affects the sense of touch
… all of these stimulate the mind and spirit of the plant lover.
But they must be coupled with a study of the inherent characteristics of a given species and its varieties to insure a full understanding and appreciation of that particular plant.
For example, in the Tacoma area there are three varieties of Rhododendron arborescens:
- One with white flowers which is similar to the type – an upright, open plant
- Another totally different in color – a magnificent, pink-flowered sort
- Third, Richardsoni – native to high altitudes where wind and weather conditions have produced a low-growing, compact, mounded form of plant
However, all three varieties have a group of common characteristics which are peculiar to all plants that make up the arborescens species. The mental concept is the determining factor in the grouping or classification of this particular species.
Rhododendron Modifications Known As Varieties
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. Their struggle for survival was a part of the violent upheavals.
Rhododendrons have two popular varieties: Catawba Rhododendron (Rhododendron catawbiense) and P.J.M. Rhododendron.
The stresses and strains of natural adjustment that made our world what it is today – also 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 their garden.
Adaptiveness, a prime value of this group of plants, has its roots deep in the origin of the species.
Rhododendron Plants “Must” Requirements
Growers in any locality who plan to grow rhododendrons should attempt to duplicate the growing conditions of their native habitat. Here are some important info about rhododendron care.
Proper Soil Is Important
Rhododendron roots are fibrous and very fine, and husky root systems will not develop in hard soils that tend to pack and become waterlogged. Unless the planting is done in natural peat, the soil must be conditioned.
Holes should be dug much larger and deeper than needed, and should be filled in with well-drained soil or “made soil,” that is loose, friable and acid. Peat-moss or leafmold and woods soil will serve the purpose, and it should be mixed with fifty 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 one inch covering. Since the top roots are for the purpose of 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, will conserve moisture and will keep the root area cool in summer.
The soil pH should be between 4.5 and 5.5. A higher factor means a tendency toward alkalinity which will result in poor development; 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 with an acid formula are fine to use in localities where the soil is alkaline, and they will usually solve the acidity problem in such situations.
In localities such as those in western Oregon and Washington, where the soil is naturally and continuously acid, no acidity treatment of any sort is advisable, for it can be harmful.
Special Rhododendron Fertilizer For These Good Feeders
Ordinary barnyard fertilizer of the bovine variety is fine for an annual feeding. Adding Epsom salts around plants in a liquid 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.
Epsom salt adds magnesium which will assist in the production of chlorophyll and prevent the development of chlorosis which is indicated by a yellowing of the leaves.
Cottonseed meal, a valuable plant food and a ready source of nitrogen, will assist in the growth of good looking 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. Where the soil is alkaline, the acid commercial rhododendron fertilizer should be beneficial.
Wind Protection For Rhododendrons Is Important
Drying winds, either hot or cold, are always damaging. Advantage should be taken of the shelter provided by buildings: fences, walls, and hedges of trees and shrubs.
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. In Puget Sound country where they have high humidity at all times and the temperatures seldom go above 85 degrees, yet heavy summer watering is necessary.
For areas without too much heat, do not over water your rhododendron plants to avoid root rot.
Protect Rhododendron Plants From Too Much Sun
Most rhododendron plants should be protected from too much sun. In hot localities, the plants must be adequately shielded front the midday sun by trees or by 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.
How To Make Your Rhododendron Plants Thrive
Plant Rhododendrons so the top roots are not more than 1 inch below the soil surface. The hole, which is dug several inches larger than the rootball, is filled in with equal parts peatmoss, leafmold and loam.
Shape a large basin in the soil around the plant and fill it with water several times to settle the soil. A temporary lath for partial shade will provide a few hours of reduced sunlight each day for the young plant if no nearby trees are of sufficient size.
Protection from wind and cold is necessary when these broad-leaved evergreens are planted in exposed locations. Trees, shrubs or structural barriers on the side of prevailing winds will prevent much damage to foliage and flowers. Rhododendron ponticum is an invasive species and would require frequent cutting so it won’t ruin other plants in the garden.
Where winters are severe a wooden frame covered with heavy burlap will protect plants against temperature extremes. Pack straw or other insulating material about the branches before setting frame over the rhododendron.
Prune Rhododendrons when the last flowers are dead. Branches cut back immediately after flowering will produce shoots which bloom the next year.
However, to insure a good floral display each early spring, it is best to cut only one-third of the branches back each year. Water pruned plants heavily.
Be sure to remove flower clusters as soon as they fade so that the dormant buds just below them on the stem (rather than developing seed pods) will receive the plant’s energy. Be careful not to damage these buds.
Propagating Rhododendrons from Stem Cuttings
After enjoying the gorgeous blooms and magnificent foliage, many gardeners want to try their hand at propagating rhododendrons from stem cuttings. Most can be propagated with the simplest equipment and technique.
Of course the very best propagation results happen where temperature, light and humidity, can all be controlled… like in a greenhouse.
But a glass or muslin-covered coldframe may be substituted with very good results.
For propagating Rhododendron cuttings make sure your coldframe is located in a well-drained area where water will not collect.
To insure good drainage, place a 2 or 3-inch layer of gravel or other coarse material on the bottom.
Spread the rooting medium on top of this, 6 to 8 inches deep. The medium may be pure sand or a mixture of half sand and half peatmoss (the latter is preferred). Pots or flats can also be used.
Then level the bed, thoroughly water it and firm it slightly.
Taking Rhododendron Cuttings
In most areas Rhododendron cuttings may be taken from mid-July to fall. Make them 6 to 8 inches long and cut them from branches of the current season’s growth.
Remove the leaves from the lower half of each cutting, taking care not to strip bark.
Then, using a sharp knife, wound the base with three upward slices into the bark, making each slice approximately 1/8 inch long and leaving a half inch between each gash.
Make the cuts through the bark only; don’t cut into the woody portion of the stem. Make the first slice at the very base of the cutting.
Next, dip the base of each cutting 1-1/2 inches deep into a plant rooting hormone powder (rootone), making certain some of the powder gets into the wounds under the bark.
Tap the cuttings gently to remove excess powder.
Then insert the cuttings (in an upright position) into the medium to a depth of one half their length, spacing them 4 to 6 inches apart. A pencil is a handy tool to make openings for the cuttings, with very little rooting powder lost.
Firm the “soil” around the cuttings, and immediately water the bed.
Place the cover on the frame, and remember to keep the sand moist at all times. A good drainage system should prevent the sand from becoming waterlogged. For the first several weeks, at least, it’s a good idea to sprinkle the cuttings with water twice daily.
Slow Rooting Process
Compared to many other plants, Rhododendrons root rather slowly. Under this method, however, cuttings taken in summer should be ready to remove from the propagation frame by late fall or spring.
Healthy-looking cuttings which have not developed roots by spring should be left in the frame.
Pot the rooted cuttings in peatmoss or a light, loamy, acidic soil. Six-inch pots are best. Place the plants in a shady or semi-shady location, and the following fall they will be ready for the garden.
Rhododendrons 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 the selection of species.
It is never wise to attempt to grow plants of doubtful hardiness in such situations.
Before anything else, it is worth noting that Rhododendrons and azaleas have minute differences which confuses many people, including the big guys in the field of botany. This has something to do with the naming system making azalea and Rhododendrons appear as the same. Due to this, their soil pH and temperature requirements may vary.
Many of the deciduous, evergreen azaleas are hardy and adaptable, and many are first-class rhododendrons. Rhododendron roseum has a multitude of clear pink flowers, and a pleasing spicy fragrance. This is a prime rhododendron, judged by any standards. This is a neglected beauty.
Rhododendron canadense is fully as good as Emerson’s poem indicates, and it is a real “toughy.”
Rhododendron Albrechti, a beautiful species with fine wide-open flowers of a deep pink bloom color, has real quality.
Rhododendron calendulaceum is highly colorful with a wide variation of 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 handsome evergreen plant, and the orchid-pink flowers are attractive in the 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.
Rhododendrons 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 racemes with lacy, foamy flowers, and 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.
Rhododendrons 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 – these are the fortunate people who are not restricted in their choice of species material.
Yet most of them fail to realize their potential blessings. This is largely due to the fact that rhododendron people have not publicized and spotlighted the species that are available.
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 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.
Let it also be said, however, that species can be used effectively in the more formal garden, or in any type of landscaping the plantsman wishes. They may want to grow only a few of these plants with other types of garden material.
Whatever their desire, there are species to suit them. Our own native evergreen species.
Rhododendron carolinianum, has slightly pinkish flowers and a very neat growth habit. The album variety of this one is a perfect jewel of a plant, with pure white flowers.
The noble reds and yellows of the deciduous Rhododendron Bakeri are scarcely known, but those who grow it in the West value it highly.
Rhododendron eriogynum is a late-flowering species with hold, 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 all its own.
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, 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 dauricum will duplicate this in February, and will have as company Rhododendron moupinense and Rhododendron leucaspis, both white-flowered.
Often the impressive Rhododendron sutchuenense, with light pink flowers that have a dark blotch, will 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 into flower the flashy, native deciduous azalea. Rhododendron prunifolium, which is a very fine rhododendron. Some varieties of Rhododendron occidentale will flower in July also.
Rhododendron discolor and Rhododendron diaprepes, both of which have white flowers, make large plants and are fine July-flowering sorts. In August. Rhododendron auriculatum, the treelike, white-flowered and slightly scented species will have as company the latest flowering varieties of Rhododendron occidentale.