Rhododendron Winter Damage and Prevention
Frost causes considerable damage to leaves, stems, buds, and flowers of some rhododendrons. On damaged plants leaves will be distorted, curled, and may grow only on one side of the main vein. Part or all of a winter-damaged leaf will be brown-colored. If too unsightly, remove the damaged leaves.
Some rhododendrons protect themselves from winter dehydration by drooping and curling their leaves as temperatures decrease. Leaf movement occurs rapidly and it is reversible as temperature warms.
Frost also will cause the bark of affected stems to split longitudinally near ground level...even peeling away. This typically happens in early fall or late spring when the plant is not fully dormant. Often these symptoms are overlooked and damage only noticed at a later date. If noticed recently after the injury and before the bark has had time to dry out the area can be wrapped with galvanized wire or a non-sticky wrapping. Check the wrapping monthly and remove the wire when the repair is successful.
Cold weather may cause branches to appear to be dead. Wait until late spring then scratch the bark on dead-looking branches. If there is green wood underneath, the branch is still alive, leave it in place. If it's brown underneath, the branch is dead and can be pruned off.
Cold weather can kill flower buds. Dead buds are brown-colored and easily break off. Often rhododendron buds are less hardy than other parts of the plant. Choose varieties that are bud cold-hardy for your area.
Because rhododendrons roots are very shallow, it's important to use a thick layer of mulch to provide protection from the cold. It'll also slow water evaporation from the ground, helping plants to stay hydrated. On warm days water your plants so they have a chance to survive cold periods.
A windbreak made from burlap, lattice or a snow fence can help prevent damage from winter's drying winds.
Finnerty Gardens has one of Canada's best collections of rhododendrons. Located on the University of Victoria grounds the spectacular garden contains over 4,000 different trees and shrubs with more than 1,500 rhododendron and azalea plants, including 200 collected rhododendron species, and a wide range of companion plants artistically displayed on a 6.5 acre site at the southwest corner of campus.
The Gardens were developed in 1974 when the estate of Mrs. Jeanne Buchanan Simpson of Cowichan Lake was left to the University. She and her husband George, beginning in the 1920's, built up a notable collection of rhododendron species at their Lake Cowichan home. Many plants were grown from seed obtained directly or indirectly from famous plant explorers of the day. Theirs was the largest rhododendron collection in British Columbia. The University decided to move many of the rhododendrons to their campus where they would form the nucleus of a new garden that was created on nearly three acres of land at the south end of the campus.
After the death of her husband, Mrs. Simpson had been unable to maintain the garden properly. The rhododendrons had to struggle for survival without the benefit of summer watering and in competition with the invading "jungle". The Simpson plants were up to 50 years old and presented a challenge to the transplanters. You will recognize these sometimes distorted giants in the Garden today. Most of them are R. decorum or R. fortunei.
The gardens have been carefully planned and developed to provide a rich and changing array of colour, scent, form and texture all year round. In April and May, you will see the rhododendrons at their best. For a plant identification guide and map of the gardens, download a self-guided walking tour pamphlet. For more information about Finnerty Gardens visit their website.
Little Sweetheart Rhododendrons
Much as I love the big, bold, beautiful Rhododendrons, I have a small garden so I grow mostly small species and hybrids. Some of my all-time favourite species are R. pruniflorum, R. sargentianum and R. campylogynum. As container specimens, all have been reliably hardy for me in the Victoria area for many years and all are easy growers.
I started with small well-rooted cuttings, originally grown in 4 inch pots and over time, have moved the plants up to larger containers. The current pot size capacities are, more or less, 3 gallons. My potting mix is coarse peat, perlite, some coarse sand and if I've got it, a bit of garden compost. I do want a well-drained mix, so there's no more than about 40% peat in the mix. I know many people are cautious about fertilizing some Rhododendron species, but I give my container-grown plants a light application of slow release fertilizer in the early spring. Since they're in pots, there's considerable leaching so I think some fertilizer is appropriate. Some of our local growers just top dress their potted rhododendrons with Seasoil (a form of composted fish fertilizer) once each spring, and this works well for them.
I keep my plants in a location where they get full sun in the morning, but by about 1 pm, they are in the shade. Good light is needed to set flower buds, so if you have some of these smaller species and they're not blooming for you, perhaps a bit more light is in order. I water freely on an as needed basis, and I make sure the drainage holes remain open since there can be problems with containers if they're sitting directly on the soil surface where the holes may gradually get plugged. I like to have some sort of top-dressing on the soil surface to prevent too much surface compaction from all the watering I do. A good layer of orchid bark makes an attractive mulch, but sometimes I use turkey grit, or small-sized pea gravel. However, if you like to show your plants, most show judges prefer to see bark mulch used as a top-dressing as they often think write comments that they think gravel isn't aesthetically suitable for rhododendrons. Personally, I like the look of gravel or grit and it lasts longer than orchid bark.
Rhododendron pruniflorum has thimble-sized bell-shaped flowers of a dusty plum colour. It's absolutely adorable in bloom. The leaves are small, a nice dark green on top and white underneath. My 6-year old plant is about 18 inches tall and 18 inches wide. Many of us grow R. campylogynum and there are several forms available - all of them are very nice. But, my favourite (and I have a couple of forms) is R. campylogynum Leucanthum. Again, the thimble-sized flowers are bell-shaped, but in this case they are white in colour. Rhododendron sargentianum has small, ball-like trusses of white to ivory coloured tubular flowers. The tiny leaves are a nice shiny green and if crushed, give off a scent. The scent isn't unpleasant, but it makes me sneeze. I have a plant of the straight species, but recently acquired a plant of the selected variety 'Liz Ann' which is stunning in bloom as it just covers itself in pure white flowers. These plants are also about 18 x 18 inches and range in age from 3 to 7 years old.
A very similar looking plant to R. sargentianum is R. primuliflorum, but, with primuliflorum, the tubular flowers range in colour from white to soft pink and even yellow. It also has scented foliage. I've just recently been given a pink flowering form of R. primuliflorum and I'm looking forward to seeing it in bloom next spring.
One of the advantages of growing plants in pots is that I can move them onto the porch when the plants are in bloom, so while the plants and their flowers are small, I can get up close and personal with them easily. You know the adage, great things come in small packages, so if you only have a small garden, consider growing some of these lovely little sweethearts.
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.