Landscape Qualities: A Rating System

by Carol Warner and Jim Wilson

Siberian irises are superb landscape plants! Their persistently neat, stiff, grasslike foliage is an asset to the perennial border throughout the entire growing season. Individual Siberian iris varieties bloom for a period of about seven to twenty-one days. The foliage, however, should be attractive for 150 to 180 days.

The garden judging section of the Handbook for Judges and Show Officials assigns 40 points to the plant. This is divided as 15 points for garden effect, vigor, and stamina; 10 points for foliage; and 15 points for stalk, buds and branching. However, our catalogs and checklists place almost exclusive emphasis on the the flowers, with very little mention of the quality of the cultivar in the landscape. Although garden judges can and do make significant efforts to include landscape qualities in considering plants in the AIS awards system, it is often only on extended observation of a variety that a home gardener can get any idea of its specific vigor and growth habits.

A reasonable approach may be to adopt some sort of rating system. Other plant societies have set a precedent; e.g., the American Rhododendron Society rates flowers and foliage on separate 1-5 scales. Ratings have the advantage of being easily compared and the disadvantage of being taken to mean other things than they actually do. Also, providing additional information in any form always carries with it the risks of error, misjudgment, and evaluations that pertain to conditions that differ from where the plant is finally grown. Nevertheless, those of us who have gotten to know the habits of many Siberian irises have developed a body of knowledge about their behavior which could be of great value to home landscapers.

The ideal rating system should be both simple and unambiguous. Providing a single number from 1-5 would be a step forward and simple, but would not tell much about the plant and what earned it a high or low rating. Writing detailed descriptions of each plant's habits could allow thorough evaluations, but could consume extensive space and time, of both raters and readers. The system described here is based on 1-5 ratings in three areas: plant vigor and clumping, foliage habits, and bloom habits.

Plant vigor and clumping: Vigorous plants that quickly establish well-formed clumps rate a 5. Slower growing plants that may take longer to reach good form and may also go longer before division are represented by lower numbers. Some gardeners who are eager to avoid the rampant growth of some varieties may seek out those rated as 4 and 3.

Foliage habits: Clean, stiffly upright foliage is rated 5. Foliage that arches slightly but stands up well through the season is rated 4, and may be preferred by some for its grace. Lower numbers indicate greater arching, tendency to collapse in late summer, and/or greater than average susceptibility to foliage problems.

Bloom habits: Varieties that hold their flowers above the foliage, preferably on branched stalks that distribute the bloom attractively, receive the higher numbered ratings in this category.

Such a rating is not intended by any means to be complete in itself, but instead to complement the information that is already available, which usually includes AIS awards received, a good description of the flower, the height, the ploidy, the season of bloom, and whether there is a tendency to repeat bloom.

One of the most challenging aspects of reporting these characteristics is the variation that results from different growing environments. At the national convention in Portland, for example, some varieties were clearly much more vigorous than they are in Maryland. Consequently, there is a very legitimate question about whether a home landscaper would be best served by a single rating for each variety, perhaps coordinated by an SSI panel, or if it is better to depend instead on independent evaluations done by a nearby grower.

A first effort at rating 60 of the varieties in the Draycott Gardens catalog has been completed over the last two years. It is based entirely on local conditions and at present makes no attempt to include information from other regions. We welcome all levels of reactions to the experiment--if the initial ratings correspond to others' experiences, if this system could be improved upon, and if the idea is worthwhile.

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