13 Feb 2006
SELECTING A ROSE PLANT (CULTIVAR) YOU CAN LOVE
By Joel Ross M.D., ARS Consulting Rosarian
Karen Dardick quoted Tom Carruth, Director of Research for Weeks Roses, in a column published in The San Diego Union-Tribune on February 5, 2006: “There are thousands of rose varieties available, all with varying combinations of color, style, habit, fragrance, disease resistance, hardiness, usefulness and panache”. The enormous variety of rose plants that are commercially available currently makes it impossible for most of us to be really familiar with any large number of them. As a result, we make selections from catalogs, bare root bins and early growth canned specimens without ever having seen the mature plant. In doing so, we boldly venture into the UNKNOWN. Venturing into the unknown is not necessarily bad, but we must adopt some realistic expectations before doing so. Purchasing rose plants without researching them (on a whim) is a bit like trying out an unfamiliar candy bar. When doing so, we realize that we might make an INAPPROPRIATE CHOICE. Nevertheless, we take a chance, pay our money, and try it. If we like it, we buy more and if not, then we dispose of it or give it to a friend (another rose society member). Some uncharitable Rosarians might characterize venturing into the unknown as the “willy-nilly” approach. If “willy-nilly” strikes you as unacceptable, then your only recourse is to develop more extensive rose expertise (READ ON).
It should be obvious from Tom Carruth’s preceding statement that it will be difficult for you to find a perfect plant for every situation. You will need to decide WHICH characteristics are the most crucial to your particular requirements. Rose Exhibitor’s make bloom form and plant disease resistance their principal concerns. Home Gardiner’s make plant habit, style and hardiness their essential considerations. Romantics make fragrance and color their primary interests. Furthermore, your own needs and expectations of the plant vary with your intended use of it (covering a fence or wall versus providing sweet fragrance outside your bedroom window). NO ONE rose plant can possibly satisfy all of your needs simultaneously.
The alternative to the “willy-nilly” approach to rose selection requires preparation by directly inspecting, reading about or discussing rose plants BEFORE YOU PURCHASE THEM. For a discussion covering bloom color, fragrance and appearance, the reader is referred to the previous article in this series. Here we will consider plant habit, form and hardiness. All of these considerations are of critical importance in your selection of a suitable rose plant. Habit refers to plant appearance: upright, trailing, climbing or creeping. Plant height (or length of canes if not growing vertically) and width is also taken into account here. You need to know these features in order to know how to correctly place plants in your garden; whether they require external supports (pergolas or other means to tie up weak branches); whether they will properly fill or overgrow the space allotted; and whether they become unruly or invasive (ramblers can grow to 20 feet). Style refers to types of plant. Oversimplified general rule descriptions are as the follows: hybrid teas (mostly 1 bloom per stem on 4-6 ft tall plant), grandifloras (hybrid teas> 6 feet tall), floribunda (multiple smaller blooms per stem on 4-6 ft tall plant), polyanthas (parent of floribundas with multiple blooms on 2-3 foot tall plant), minis (size refers only to the bloom, plants can vary from 18 inches to >6 feet tall), mini-flora (minis bred for larger than usual blooms), climbers (taller than 8-10 feet), and ramblers (overzealous plants with up to 20 foot canes which can become invasive). This list of styles is not exhaustive. You need to know about plant style in order to create a harmonious effect for you garden. If you are uncertain as to either the style or the habit of a plant that you have already purchased, DON’T put it into the ground until you have consulted a reference or found an experienced Rosarian or Nurseryman to help detail these for you. Hardiness refers to a plant’s ability to thrive in the intended habitat, its ability to withstand the extremes of heat, cold, humidity, shade, soil conditions and available water that it will encounter in your garden. You need to have this knowledge as well if you expect to avoid disasters.
The importance of one aspect of hardiness, that relating to natural disease resistance CANNOT BE OVER EMPHASIZED. Roses vary by cultivar as to their disease resistance. Disease resistance is relative, NOT absolute and does vary even in a single cultivar by the specific disease. Rust is a fungal disease creating disfiguring brown-gold gritty spots on the undersurface of leaves caused by multiple Phragmidium species. Powdery Mildew is a fungal disease creating a white powdery fluffy growth on the top of leaves caused by Sphaerotheca pannosa. A great number of different fungi create black spots that are seen on the leaf surfaces. Only one of these many fungi, Diplocarpon rosae, actually causes the dreaded disease called “Black Spot”. The actual disease “Black Spot” has 1/20th inch generally circular black spots with yellow margins and a feathery edge. This disease is a threat to the plant’s life because it can cause near total defoliation. ALL the aforementioned fungi invade the leaf substance rather than just being cosmetic surface blemishes. There one major fungal disease of the plant’s vascular system, Downy Mildew, is caused by Peronospora sparsa. It appears as purplish blotches on the leaves and a red-purplish discoloration on the canes during wet cold weather periods. It also can threaten the plant’s life by near total defoliation. As the growing season wears on, the vascular injury to the canes by Downy Mildew is either controlled by plant defenses (cane re-greens to some extent) or progresses until the canes become devitalized (cane blackens and dies). New and more recently introduced commercial rose plants (sprouted since the mid 1990’s) that are susceptible to these fungal diseases are destroyed in the greenhouse germination sheds regardless of other redeeming characteristics. Unfortunately, older roses already in commerce are more likely to be susceptible to these problems. Current Rose Horticultural practices for preventing and treating these diseases include a variety of organic and chemical sprays as well as attention to the proper care and maintenance of the soil ecology. Rose disease problems have in large part been responsible for dissuading gardeners from raising roses but newer cultivars are beginning to make disease control MUCH EASIER AND SAFER.
Knowledge of the above-mentioned characteristics of cultivars that you are considering adding to your garden allows you to make better choices. You will be more likely to purchase plants that will serve their intended purpose. However, since it is imposible to avoid the occasional “mistaken purchase”, the next article in the series will detail how to identify and rid you garden of the “losers, mistakes and dogs”.
* Note from the Ross Garden Director, my wife, Linda: Despite the above logical method of choosing rose plants, I continue to use the “willy-nilly” approach.
Joel Ross M.D., ARS Consulting Rosarian