Cold Hardy Camellia Families
Cold Hardy Camellia Families
With the development of cold hardy camellias, gardeners are enjoying camellias in regions where they've never grown before! Growing camellias beyond the Camellia Belt requires decidedly different cultural practices than those recommended in the south.
Growing Camellias in the Northern Landscapeby William L. Ackerman
Growing camellias beyond the Camellia Belt requires decidedly different cultural practices than those recommended in the south. I have emphasized in both my camellia books, that where Northerners follow traditional southern practices, they invite disaster. The bulk of this article will explore the do’s and don’ts for the Northern gardeners with explanations of the differences.
The southern grower’s concept of what constitutes hardiness primarily centers on the hardiness of the flower buds, and much less on that of the plant. This is natural because their greatest concerns are with the occasional freeze immediately before and during the blooming season. On the other hand, the northern growers are concerned primarily with plant survival, with flower damage being of secondary importance. Selecting camellias based on flower versus plant hardiness can lead to very different results.
Planting camellias in the fall in Maryland and northward (a frequent practice) is a risky business at best. If the first winter is mild, one may succeed; if it is not, it can cause the death of the plant. Soils can cool rapidly after mid September and new root development is usually minimal. Yet, every Camellia book I have ever read (written exclusively by authors living in mild climates) recommends fall planting. A popular time in the South is at the time of leaf fall of the local deciduous trees. The logic here is to allow the plants to get established during the anticipated mild winter in preparation for the stress of the southern hot summer that will follow. This is absolutely the worst time of the year for northern camellia growers. In contrast, northerners need to rely on the relatively mild summers to prepare the plants for the stress of their first winter.
Unfortunately, some northern nurserymen further this concept by promoting the fall flowering cultivars while they are in bloom and most salable. This problem could be moderated if they cautioned their customers about providing winter protection the first winter. We, in the North, have recommended spring planting for many years, preferably between mid-April and late May. We also recommend using Microfoam (or burlap) shields around camellia plants during the first winter. In selecting a suitable site for a new planting, the gardener will undoubtedly need to make compromises. Few of us are blessed with an ideal location. Avoid planting near shallow-rooted trees such as birches, beeches, some maples, and other moisture robbers, such as privet. These usually win in any competition for moisture. We need to make the best choices of the various sites and exposures available to us. However, in some cases, we can overcome local problems through the use of strategically-placed fences, hedges, and/or wind-breaks.
The following is a general description of those characteristics one should strive for, and those that should be avoided if possible. Contrary to popular opinion, the best location for camellias in northern regions is a north or northwestern exposure with protection from the prevailing winds. This can be accomplished through shielding by one or more buildings, a substantial wall, or a conifer hedge (like fast-growing Leyland cypress). Here, the plants will, hopefully, go into a state of dormancy in the autumn and tend to stay that way. Plants exposed to wide fluctuations in temperature do not reach their optimum potential dormancy. It is the sudden change to sub-freezing weather that can be devastating. In northern areas, it is generally accepted that exposure to very early morning winter sun can be detrimental to plant health by causing leaf burn, or even plant death. The rationale here is that when the surrounding temperature is well below freezing, the sun shining on dark green foliage can create a microclimate over the leaf surface that is as much as ten to fifteen degree above that of the surrounding air. With the low relative humidity that frequently exists during cold winter mornings, moisture is drawn out of the leaves, creating desiccation. If the ground is frozen, the plant cannot readily replenish this moisture from the root system. Thus, under extreme conditions, the foliage will turn a pale greenish white and become as brittle as corn flakes.
Basically, nature has created conditions similar to what we know as freeze drying. As a result, the leaves are killed and the plant will suffer partial or complete defoliation. The solution here is to provide some shade protection during the winter months. The degree of plant dormancy directly before a sudden drop to sub-freezing temperatures can make a life or death difference. More a problem in the South, we are also susceptible in Maryland and northward. During the second week of January 1985, temperatures held in the mid 50oF range (10oC), followed by -10oF (-23oC) in the third week of the month. Plants with southern exposures had more leaf burn than a comparable group of cultivars in northern shade. Apparently, the first group had begun to lose some of their dormancy. These same plants had been subjected to comparable low temperatures in previous winters without injury. It has been found that the seventy-two hours prior to a severe drop in temperature can be most critical. Plant dormancy is also influenced by the use of high nitrogen fertilizer late in the season.
Studies with fruit trees have indicated that low nitrogen and high potassium and phosphorus can decrease winter injury by increasing the soluble salt content of plant cell sap. One does wonder whether there is a relationship between this phenomenon and the observation that often individual heavily blooming branches on fall flowering cultivars tend to be more severely winter-damaged than their sparse blooming companions. Could the drain on plant nutrients in that branch make it more vulnerable? The greater susceptibility of some grafted plants to winter injury compared to those grown on their own roots may depend upon the degree of compatibility between stock and scion. Any graft union that tends to inhibit the free flow of nutrients and water between the plant’s roots and top may be less capable of withstanding environmental stress. Similarly, a plant’s ability to replace water lost from transpiration can have a direct effect on its capacity to withstand stress. Light sandy soils have a limited capacity to hold moisture, while heavy clay soils can reduce root development. Neither condition is conducive to healthy plant growth. Also, the amount and frequency of watering can be very important. Less frequent, but thorough watering encourages deep root development, while frequent light watering increases shallow rooting. Naturally, the latter plant will be less capable of dealing with environmental stress than the former.
Camellias prefer a well-drained, slightly acid soil (from a pH of 5.5 to 6.5), and will tolerate more acid conditions, but go into a slow decline under alkaline soils. The soils around newly constructed buildings or near new concrete sidewalks, walls, driveways, or patios, can produce high lime runoff causing decline and death of nearby camellias. Where there is a slope, plant near the TOP, not the bottom, of the incline. Also, avoid a low frost pocket where the surrounding ground on all sides is higher. On still nights, cold air being heavier than warm air, flows down hill like water and accumulates wherever it is obstructed from its downward movement, be it a wall, building, or compact evergreen hedge. I once observed frost damage in a peach orchard while it was in full bloom. The rows of trees contoured along the slope. Blooms on the lower rows were all killed up to a middle row where the blooms on the lower half of each tree were killed. However, blossoms on the upper half of those trees and on the trees up the slope were uninjured.
Growing camellias in the northern landscape, as emphasized in this article, is not without risk. However, there are also some advantages. We have not been plagued with such diseases as petal blight, dieback, canker, among others. Yet, we should not brag too soon. Last year, I observed petal blight in our outdoor plantings for the first time in more than 40 years. Prior to that, I had only experienced it in the greenhouse – the result of contaminated container plants purchased from a California nursery. My unofficial conclusion – globular warming. This may, in addition to the greater hardiness of the C. oleifera hybrids, partially explain why we now have camellias growing in Nova Scotia and Toronto, Canada, and most recently Norway. One inspiring trait of camellias is their unique ability to rebound after a bad winter! Never give up hope! Many camellias will sprout from the trunk as late as June after a bad winter. By the end of the second or third season, they will have regained much of their former size and vigor. A true resurrection!
This all leads to a greater incentive to grow and cherish this most beautiful of ornamentals. Breeding camellias for the northern landscape is an on-going process. In my own case, if I think back to the late 1970’s, we started with two C. oleifera introductions, “Lu Shan Snow” and “Plain Jane”, both with single white flowers. These were hybridized with a large group of standard cultivars, which were tested for many years and resulted in the selection of 34 fall blooming and 15 spring blooming, deemed both cold hardy and of high quality flower and plant characteristics, to be registered.