Selecting Rhododendrons For Your Garden
Over 30 years ago I purchased my first rhododendron for a Mother's Day present. I still have a vivid picture of proudly presenting it to my mother on Sunday morning, after selecting it the day before from a local nursery.
Like most beginners I was looking for a big plant with lots of blooms that didn't cost any more than a 16-year-old boy could afford. However, with the passing of time I now realize I was fortunate to have purchased a quality plant without really knowing what I was doing. Today, when I purchase a new variety, several criteria come to mind before I make my purchase. The following general topics are not necessarily in any specific order...but seem to be worth consideration prior to selecting a plant.
Learn about climate. Get knowledge of local climatic conditions, with special attention to the most extreme winter temperature in the past five years. This extreme cold temperature is critical as most rhododendrons sold are rated for hardiness. The hardiness rating is a generally accepted temperature that the plant will endure and survive. Notice: I said the plant...and not the flower buds. The rationale behind plant hardiness is that you can afford to lose the buds on a given year, but not the plant.
Talk to local gardeners. Talk with neighbors and rhododendron club members about varieties that they have had for several years. Discuss with them how frequently the plant flowers, when it blooms, and where in their yard they have it located, i.e., in partal shade, in full sun.
Read about rhodies. Background reading about rhododendrons on the world-wide web or in one of the reference books is helpful. Several of the books have many excellent color pictures. Would recommend any of the following authors as good resources: Van Veen, Greer, and Cox. Each of the authors provides good description of flowers, plant habit, bloom period, and hardiness in a very understandable form.
Visit nurseries. Visit several local nurseries, if available, to view their selection of rhododendrons. Find a rhododendron knowledgeable sales person and seek opinions about varieties that do well locally. Generally, retail nurseries tend to sell "tried and true" varieties that have stood the test of local time. Frequently, your choice will be quite limited in the number of different varieties that are available.
When you have all of the general information identified and are ready to make your selection...that one plant to be located in that special place in your yard...suggest you have the following in mind:
Ultimate Size. How large will the plant be at 10 years of age. Standard varieties are about 6 ft. at 10 years. Semi-dwarfs are about 2 to 4 ft. at 10 years, and dwarfs are about 1.5 ft. at 10 years of age.
Plant Age. Know the plant size you want to purchase. Are you after instant landscape...or are you willing to strat small and allow the plant to go over time.
Location. Know the variety you want meets the conditions of your location, i.e., full sun, semi-shade, etc.
Plant Health. When you make the final choice, the foliage of the plant you select should be green and healthy looking. It should not have burned or spotted leaves. Burned leaves generally result from inadequate water in the summer, or excessive cold in the winter. Leaf spotting typically results from some disease condition. Stay away from lopsided or crooked plants. The leaves should be free of insect damage. Notching around the border of the leaves generally indicates weevil activity. Other insect damage is evidenced by irregular holes in the leaves. If you want the plant to bloom in the coming season, look for large flower buds on some of the branch ends.
Personally, I realize that initially all of the above takes a great deal of time...but your labors dramatically increase the chance of purchasing an excellent rhododendron. All too often we buy the plant with the big open flowers, only later to realize, it was a mistake.
Growing Media pH
What is pH, and how do I obtain the proper pH for my rhododendrons?
The term "pH" refers to the acidity of a material. Technically, it is a measurement of the hydrogen ion content. The pH scale ranges from 0 to 14 and pHs of 0 to 7 are acidic - pHs of 7 to 14 are referred to as being basic or alkaline. A pH of 7 means the material is neutral.
The experts indicate rhododendrons prefer an acidic medium. The preferred pH should be between 5 and 6.5.
It is almost impossible for a layperson to determine the pH of the potting medium they use. There are pH meters on the market...but in my experience the ones that cost less than $100 are practically worthless. I have yet to try one that is better than plus or minus 1 pH.
But...all is not lost. It is actually fairly easy to get your pH in the desired range. Fir or hemlock bark is almost always in an acceptable range and, therefore, an ideal medium to use. It is best if the bark has decayed or mulched for six months prior to use.
The reason pH is important for plants has to do with the intake of minerals and nutrients. If the pH is too low, yes, soil can be too acidic, the plants have difficulty taking in the nitrogen and phosphorous they need for growth.
The foliage will not be the rich green that you expect. Adding lime to the medium or the soil will raise the pH and help this condition. Too low pH can occur when soil has been fertilized heavily for years. The fertilizer frequently increases the acidity of the soil...that is...it lowers the pH.
If the planting medium of soil is too alkaline, i.e. the pH is too high, it usually causes iron and/or manganese deficiencies. These deficiencies result in chlorosis - a condition where the veins may remain dark green - but the spaces between the veins will be yellow...the leaves are said to be chlorotic. To remedy this condition sulfur is often applied for a quick fix. Good mulching will also help in the long run. A decomposed mix that would not use up the nitrogen in your fertilizer is best.
In summary, pH is important but your plants will tell you if you have a problem. Generally, it is always best to use bark in pots and bark or pine needle mulch as an additive for your soil...and you will rarely have a problem.
Companion Plant: Viburnum bodnantense
The winter-flowering Bodnant viburnums are tall, fairly narrow shrubs which have bunches of tubular pink flowers on leafless stems. They bloom in late winter and have frost-resistant blooms which stay for weeks and are quite fragrant.
The species name 'bodnantense' refers to Bodnant Gardens, North Wales, where the hybrid was raised in 1935. The Bodnant vibumum grex (a grex denotes all the offspring of a particular cross) is a cross of the Chinese viburmum farreri with the Himalayan viburnum grandiflorum and, includes the cultivars 'Dawn', 'Charles Lamont', and 'Debian'.
'Dawn'...often called 'Pink Dawn'... is commonly grown and is widely available. 'Charles Lamont' has dark pink flowers which are somewhat larger than 'Dawn'. 'Debian' is tall and has a stiff habit with slightly fragrant whitish flowers which turn red with age.
'Dawn' is a deciduous upright shrub, 2-4 m. (6-12 ft) in height. It blooms in Fall and Winter after the leaves have fallen. Before they fall, the leaves turn a burnished bronze color. Red buds open to fragrant pink flowers that fade to white flushed with pink as they age. Wet weather and frosts may limit flowering display. Branches can be forced inside for a winter bouquet. The fragrance indoor may be somewhat overpowering.
Photo by Giraffenigel
'Dawn' is not particular as to its location, liking sun, but also doing well in partial shade. It enjoys acid, well-drained soil, but does well enough in other soils. It is fairly cold-hardy...but requires a protected placement where the chilliest winds won't hit it at temperatures below zero degrees F. Overall, this hybrid is very adaptable.
Since the plants are fragrant, grow them near a path you are like to use frequently. You will be rewarded! Otherwise, you won't appreciate the scent at a time of year when you're less inclined to go down a damp cold garden to smell it. The flowers have a pleasing perfume. The new leaves get so large that the blooms occurring the rest of the year can pass unnoticed. The leaves smell like citrus if crushed or bruised.
Fertilizer Nutrient Elements
A bag of fertilizer has three numbers prominently featured on the label...something like...5-2-0. It's important to know what those numbers mean because the wrong combination can do more harm than good. The numbers indicates the amount of three major plant nutrients: nitrogen, phosphorus, and potassium, abbreviated NPK.
One way to remember what those things do, and keep them straight is the phrase "up, down, and all around." Nitrogen is needed for green, leafy growth...the up. Phosphorus helps produce healthy roots...the down. Potassium is important for overall plant health and resistance to water or insect stresses, so it's...the all around.
Plants need anywhere from 14 to 18 plant nutrients for best health and production. Magnesium and sulfur comprise the macronutrients along with NPK. The micronutrients include: iron, manganese, boron, zinc, copper, molybdenum, and maybe chlorine. Testing your soil is the way to determine what is needed.
Success With Heathers
The singular species, Calluna vulgaris, inhabits large portions of Europe and northern Africa, from Siberia to Morocco, in vast tracts of open land and hillsides. The predominant flower color is purple...but it sports out in pink, red, and white. For well over 100 years, avid plants men have made over 500 selections of form, bloom, and foliage variations, and some of them are real eye-poppers!
Now, if you are one of those people that think that they always look so ratty, I am about to show you the error of your ways. Site selection is probably the most important factor. These are ericaceous plants...in the same family as rhododendrons...and like them, we should take our lessons from Mother Nature. Full sun is an absolute must and some slope to the ground is very beneficial. Soil should drain well, but retain some moisture, especially in summer during bloom time, anywhere from July to November depending on cultivars. An acid, humus-rich soil with no manures or strong fertilizers is necessary...a lean media keeps the growth compact. If you cannot engineer even a bit of a slope, then be sure that the soil is deep and loose. And then...prepare to PRUNE!
Ok, ok, and ok! I know no busy band of elves prunes on the moors, but truth be told, if you took aside only one or two of those million of plants, they probably would be ratty...but there's safety in numbers and distance. We do not have that advantage in our gardens...so get out the hedge clippers. March is a good time to do this...trim just to the bottom of last year's flower spikes to make a somewhat mounded shape. Now, was that so hard? Once a year is all it takes, and a spring pruning still lets you enjoy all that wonderful winter foliage on the colored forms.
Choosing varieties for your garden will be by personal preference. With that many to pick from, it is like roses or rhodos...grow the ones you like to look at. I can only give guidelines of the forms that are available. The flowers can be single or double on long or short spikes. I have taken full open spikes of 'Peter Sparkes' and 'H.E. Beale' and hung them to dry, and they make wonderful bouquets...unfortunately, not too durable...but so easy you can do new ones every year. Colors range from white and pale pink to bright pink, crimson, and purple. There are varieties like 'Marleen' that seem to bloom forever since the blossoms don't ever actually open, just show outer color.
The foliage on some is so spectacular that even if they didn't bloom, no one would notice. Red-gold ones like 'Firefly', 'Blazeaway', 'Boskoop', and 'Sir John Charrington' are bright all year round. Silver ones like 'Jan Dekker', 'Silver Knight', and 'Grey Carpet' will gleam against dark backgrounds. Some like 'Spring Torch' and 'Spring Cream', have colored foliage on new growth only...almost like an early bloom...and then the proper flowers come later. Very dwarf ones can be used in troughs or rockeries, as 'Foxii Nana', 'Dainty Bess', 'Humpty Dumpty' and 'J. H. Hamilton'.
The list is endless...but this should give you an idea of the lovely ones there are to choose from. Visit gardens and plant centers in summer when they are in bloom. I only wish I had more room in my garden to have an entire bank devoted to them...in drifts of all year color.
Rhododendron williamsianum, introduced to horticulturists of the western world in 1908 by Ernest "Chinese" Wilson is at once one of the most recognizable and one of the most enchanting rhododendrons. Its unique combination of almost orbicular, mid-green leaves, spreading and somewhat rounded or dome-shaped habit, and disproportionately large, candy-pink, campanulate flowers make it easy to recognize and well-adapted to gardens both large and small. Its densely mounded shape often has a somewhat brooding appearance, a bit like having a very large toadstool in the garden...but its solid presence makes a good anchor to a plant grouping, and can provide an effective screen, if needed.
Although never thought of as a large rhododendron, it can in time become quite massive, spreading up and out in large billowy curves that are certainly beyond the reach of vertically-challenged gardeners.
Photo by Chris Klapwijk
It was a species that has so captured the imagination of rhododendron fanciers that a veritable frenzy of hybridizing ensured. After all, there were so many positive characteristics to try to attach to other rhododendrons: small, tidy, glabrous leaves, with lovely bronze new growth, well-shaped, pretty pink blossoms that were large in relation to the leaf size, and a spreading compact habit that keep the blossom down where people could easily admire them.
Looking through Salley and Greer's book Rhododendron Hybrids, I gave up counting at the end of the C's, having reached something over 55 hybrids. Each decade seemed to bring on a new wave of williamsianum crosses:
- Rothschild in the early 30s, including the iconic hybrid 'Bow Bells'.
- Lord Aberconway in the late 30s and early 40s, with a whole series of hybrids beginning with "A" ('Adrastia', 'Adrean', 'Amata') as if he were trying to get in first in the Yellow Pages, but also developing the wonderful 'Cowslip', a williamsianum x wardii cross.
- Hobbie in the mid 40s, with his 'Gartendirektor(s) 'Glocker' and 'Reiger'
- all the way up to Weldon Delp and Hans Hachman's more recent hybrids.
- Even J. C . Williams of Caerhays Castle used this namesake rhodo in his inspired 'Hummingbird' cross with R. haematodes.
R. williamsianum is truly endemic to Sichuan, China, being found only there, and even within that province its distribution is very limited. However, it is now in constant and widespread production and cultivation all over the world.