He was rapidly joined by many other enthusiasts and professional horticulturists as Canna hybrids enjoyed rapid popularity in France, and later the rest of Europe and North America.

The phenomenon of the sap rising in early spring months helps to explain why arborists and professional horticulturists caution about pruning trees and shrubs too early in the year.

Ms. Britton has designed many roof gardens and now leads workshops on the importance of their infrastructure for Metro Hort, a group of professional horticulturists in the city.

The Bartlett Arboretum Association, which is the planning and advisory group, has 650 members and sponsors courses and programs geared to professional and amateur horticulturist alike.

Ms. von Gal cited the many plant societies, as well as Metrohort, a group for professional horticulturists, which meets at the New York Horticultural Society's home on West 58th Street.

Some are professional horticulturists; others represent environmental-action groups.

The SUPERthrive product has many adherents, not only professional horticulturists, but, according to its packaging: "US Departments of Agriculture, Army, Navy; states, cities, counties, universities."

Park Seed Company's annual Flower Day is the only day each year when the company's professional horticulturists give guided tours of the gardens.

Most professional horticulturists who saw the original plan believe that the design, as presented, is horticulturally "illiterate" and have raised serious questions about its viability as a living garden.

The professional horticulturists have divided daffodils into classes, which are segregated by the size of the flower's cup (trumpet or corona) or if the daffodil is a special kind of hybrid.