The factor most commonly evaluated in plants is their ability to survive cold temperatures, as many ornamental plants originate in mild-winter climates. Roses can be very roughly broken into three groups as regards cold-hardiness: those that will tolerate rather cold temperatures, at least 10 degrees or more below 0° F; those that tolerate temperatures down to 0°F; and those that can be killed by prolonged periods below 20°F. This is a broad simplification, but one with general merit, and allows us to look at a breaking point in the USDA zone chart of Zone 6, where average minimum temperatures range from minus 10°F up to 0°F. Many roses which will thrive in zones 5 and 6, and with careful covering of the plants with an insulating blanket of mulch, many more will survive. However, temperatures below -25°F are too cold for many roses which will grow in zones 5 and 6. For gardeners living in those colder climates we suggest you read the following brief article by James Sagmiller, who grew many hundreds of roses in his garden in Montana for years. And as a general guide we offer a basic table which groups the classes of roses in this catalogue (very roughly) by the three groups of cold hardy types discussed above. Some complex groups like the Modern Shrubs include a very wide range of hardiness/tenderness and cannot be easily generalized.
The zero-degree Fahrenheit point is a significant breaking point for roses, which is why the Brownells of Rhode Island nicknamed their group of hardy hybrids Sub-Zero roses. Many breeders since the Brownells have worked toward breeding very hardy roses. The hardiest species have been used, particularly the repeat-blooming Rosa rugosa. To avoid the suckering habits and thorniness of the Rugosas, some breeders, like Kordes in Germany, have worked from Rosa wichurana, whose less thorny stems and smooth foliage are more akin to the qualities found in the popular Hybrid Teas. Creating a garden of roses in a very cold climate can be a challenge. For those who brave this challenge we offer a few additional pointers. Among the Modern Shrubs are many very hardy roses. We particularly recommend you try those introduced by Buck, Kordes, Lens, Noack, Poulsen, Svedja, and Tantau, many of which are likely to withstand the rigors of very cold winters. There are few very hardy climbing roses, but among once-blooming Ramblers are a few groups worth investigating: the Ayrshires, Multifloras, Setigeras and many of the Wichuranas. These you will find enumerated on page 181 in our catalogue.
Old Roses for Cold Climates
by James Sagmiller
Many of the old roses are extremely winter-hardy and of great value in colder areas of the United States. They are easy to grow and do not require winter protection. Most of these very hardy roses bloom once in a season, for about three to four weeks, in summer.
Of the Species, the following are extremely hardy: Rosa cinnamomea plena, Rosa californica plena (pictured here)and the ancient hybrid we know as Rose Pavot (G).
The Spinosissimas, Gallicas, Mosses, Centifolias, Albas, Hybrid Eglantines, and Rugosas are very cold hardy. All will surely bloom after a -25°F winter, and the Spinosissimas and many Rugosas will bloom after a -35°F winter.
The Damasks, Hybrid Chinas, Hybrid Bourbons, Damask Perpetuals, and repeat-flowering Mosses are semi-hardy and should be able to bloom after a 0°F winter without protection. If you are in an area that gets colder than this, you can plant them next to a south or east wall. Be sure to allow for mature plant size: put them at least 18 inches away from the wall, and do not plant beneath an overhang where soil will be very dry. The Damask Perpetuals and Mosses can be soil-mounded for the winter and thus grown easily where temperatures drop to -40°F or even lower.
Hybrid Perpetuals and Bourbons are hardier than Hybrid Teas but should be winter-protected where temperatures go below 10°F. Hybrid Teas, Floribundas, Climbers, Chinas, Miniatures, English roses and Hybrid Musks should be winter-protected where temperatures go below 15°F.
A good way to protect roses for the winter is to mound soil about 12 inches high over the crown of the plant, leaving no air spaces. Do this after frosts begin in the fall, but before the temperature drops below 15°F at night. Water the mound to dispel air spaces and soak the plants before winter. Remove the soil mound gradually in the spring, about one inch a week until the last bit is removed after the last frost. Prune away dead wood about midway through soil removal, before buds break.
Remember that if you give your roses the best spot you have, full sun, rich deep soil, plenty of water, and protection from wind, they will grow better and withstand cold winters more easily.
Heat & Humidity: Roses for Southern Climates
Heat is a factor that affects roses perhaps as much as cold, as many a gardener in the southern United States will attest. In California we observe a remarkable difference between the performance of a rose grown in the northern part of the state and the same variety grown in the southern part, and the degree of summer heat often provides the greatest difference. Nowhere is heat a more significant factor than in the Deep South where heat combines with humidity to stress many roses in the extreme. Southern gardeners have long recognized the uniqueness of their climate, but in recent years, with the revival of old roses, they have also come to recognize those classes of roses that truly thrive in their hot, humid summers. Hybrid Teas are difficult to grow to perfection without constant protection against disease, but the old repeat-blooming classes thrive, particularly the Teas, Chinas, Noisettes, Tea-Noisettes, Musk roses, and the Banksias (pictured here).
Lack of cold can be a part of the problem in some southern climates, where the old once-blooming Gallicas and Centifolias can perform very poorly because they fail to experience a dormant season. Those Old European types can be enjoyed in the form of the Hybrid Chinas, crosses between Chinas and Old Europeans which look like Gallicas, Damasks and Centifolias, and which do not require the enforced dormancy of winter chill to bloom well.
Roses which are derived from the Chinas or Teas often perform well in the South, as do a number of species which originate in the mild climate of southern China, notably Rosa banksiae, Rosa bracteata, Rosa brunonii, Rosa gigantea, and Rosa laevigata. Some, like Rosa laevigata, have been so successful that they have escaped into the wild and become ubiquitous. Two hardy species from the Orient, Rosa wichurana and Rosa multiflora, are very hale and healthy in the South, and R. multiflora has even become a major weed pest, seeding itself all too freely on the edges of woodlands. Hybrids of these two rambling species are well worth growing, particularly those hybrids between Tea roses and Rosa wichurana, which were bred in France in the early twentieth century.
For those who want to garden with roses in hot, humid climates, and do not want to work hard to make them thrive, we recommend these tried and true old roses of the South. But we encourage you all to stretch the boundaries, and not to give up on roses you may want to grow. Our friend Rosemary Sims of New Orleans showed us that many old Hybrid Teas thrive in that steamy climate, and challenged the claims of some writers who said that Rugosa roses could not be grown in New Orleans. She brought in some dozens which grew and bloomed beautifully. And in Charleston, Ruth Knopf continually raises the bar, growing roses that others have not succeeded with, and doing it with a minimum of fuss.
The Perfect Rose for Every Climate
Every year new roses are introduced with an expensive fanfare of mass-marketing to our nation of gardeners, as though one rose will survive the rigors of all climates. Few of them succeed in even a handful of American climates, yet the purveyors of new roses keep trying to convince us with their new introductions. There are perfect roses for every climate, but they are different roses for each climate in America. All we need do is look to the past, to the old roses that survive at old homesteads, and on roadsides, in neglected cemeteries and springing from the pavements where we live.
All plants live by the elements, though sometimes gardeners forget that and allow themselves to believe that all that roses require are “systemics.” If we truly ask the question, “will this rose thrive in my garden,” we must look beyond cold-hardiness. Their needs are simple, and we can usually find the right roses to suit the conditions at hand in our gardens.
Of prime importance is soil. From it a plant derives many of its needs. Soils may be rich or poor in organic matter, and the gardener’s job is to supply organic nutrients when they are lacking, and again when the plant has used them up. We recommend a healthy application of organic mulches to the soils on a yearly basis. Alfalfa pellets can be added to mulches to contribute enzymes that stimulate growth in roses. Soils may be alkaline or acid, and roses show their preference for acid or neutral soils by becoming chlorotic or yellow-leaved when grown in too alkaline a soil. The “salty” or mineral-rich conditions in an alkaline soil can be counteracted by leaching, or drenching the soils with acid to neutral water. In recent years the addition of epsom salts (magnesium sulfate) to the soil has been recommended by some writers to encourage the production of new basal canes on roses. The wise gardener will test her soil before adding anything to it, but particularly before adding mineral salts that will move the soil pH toward the alkaline side. A soil test, moreover, will provide a clear picture of the invisible makeup of the soil you are gardening in, making your job a much simpler one.
Air is as important to plants as it is to us. The process of photosynthesis requires carbon dioxide. An open, well-ventilated site will do much to allow roses to thrive. Conversely, crowding roses, walling them in against houses and fencing, can create the very conditions that diseases thrive in. Crowded plantings of roses provide the ideal situations where diseases will rapidly move from one plant to the next. We suggest spacing your roses, combining them with other plants including perennials, bulbs, and other flowering shrubs. Not only will the roses benefit but they will be joined to a more beautiful and natural garden scheme. Air in its most palpable form, wind, can wreak havoc on a planting of roses. We recommend providing shelter when possible through windbreaks, as well as selecting roses that are more resilient in the face of wind, particularly the old roses and the species, and especially the many forms of Rosa rugosa.
The energy of sunlight is the source of fuel for all plants, and roses require a good 5 to 6 hours of sunshine a day to be healthy. Exceptions to this rule do exist, and we invite you to read the next section to learn more about roses for shady conditions.
All plants need water, a requirement that is often misunderstood. In our summer-desert climate in California we have no rain for a space of 4 to 6 months each year. Despite that annual drought, roses thrive in neglect once they are established. Like many woody shrubs, roses can bury their roots very deep in the soil, accessing hidden moisture through the summer and fall. We encourage gardeners to grow some of their roses completely without summer water, particularly those that are once-blooming, once they have begun to achieve a mature size. In contrast, some gardeners are faced with soil conditions that are extremely wet, particularly during rainy seasons. Few roses tolerate growing in soils that are constantly wet, but many will survive annual flooding, as long as the soils drain within a few days. The swamp rose, Rosa palustrus, thrives on the wet bank of a pond or stream.