Another issue is floral display, meaning quality and quantity of blossoms and how long they bloom. Consumers want it all, boffo flowers all summer long, and some plants do deliver. Hard-core gardeners call these overachievers "floriferous," which sounds precious but now you can pass for an insider.
The third issue Coombs and other plant testers look at is hardiness. For perennials, this usually answers the question how low can the temperature go before they croak? We think annuals, though already hardwired to die off when the weather gets cold, deserve a medal for surviving a soupy Philadelphia summer.
Issue No. 4 is disease resistance. For example, how likely is a plant to get powdery mildew? This is a fungal disease that appears with depressing frequency as a whitish fuzz on leaves. In severe cases, it causes them to drop off, but mostly it makes you look like an incompetent gardener.
Long, self-serving story short, a plant trial should answer one pressing question: Could this thing ever make it in my garden?
"Not every plant is meant to be in every garden. That's kind of the fact of the matter," says the unfailingly diplomatic Coombs, who has just completed a two-season trial of annual hybrids of the native North American coreopsis.
Colorful and compact, these sun-loving, daisylike annuals mound up nicely, as much as 18 inches tall and 24 inches wide, just right for containers and mixed beds. They also have a marketplace profile that Coombs appreciates: Coreopsis is one of the most popular plants on the market, with new varieties being developed all the time.
Why not offer consumers some unbiased guidance in choosing the best ones?
This is the latest in a series of plant trials at Mount Cuba, a 600-acre public garden on the former Copeland estate dedicated to every aspect of the Mid-Atlantic region's native flora. Other recent or ongoing evaluations in Mount Cuba's 15,000-square-foot trial garden involve native asters, coneflowers, heucheras, and perennial coreopsis.
The annual coreopsis trial is the first to include an "ecological value" component, in which University of Delaware horticulture students track how hybrids bred for a particular quality or characteristic compare in this vital function to their native-parent species.
"We want to make the tie-in that plants are not just plants," Coombs says. "They interact with the environment at large."
Students are monitoring feeding habits of caterpillars and leaf-eating insects and also bees, both honey and native, from five colonies at Mount Cuba, to determine how much pollen and nectar they consume from the various coreopsis plants, what the foods' nutritional value is, and other factors.
The data will be turned into a digital pollen library this year.
"Instead of just looking at how pretty a plant is, we're looking at how it attracts pollinators and whether this is a good, nutritious source for this pollinator," says Deborah Delaney, assistant professor of entomology at the University of Delaware and supervisor of this component of the trial.
"Owen Cass, a graduate student working on the pollinator study, believes consumers choosing plants with a high ecological premium should not have to sacrifice aesthetics.
"We hope to show people there are plenty of options," he says.
And so, while the ecological component goes on, other trial results are in. Coombs nominates these five annual coreopsis, from 27 varieties tested, for "outstanding garden performance":
"Jive:" masses of white flowers with burgundy eye and orange center. Eye-catching in containers.
"Salsa": gold flowers with burgundy eye and orange centers.
"Golden Dream": cheerful, sunshine-yellow flowers.
"Pineapple Pie": golden-yellow flowers with cherry-red centers.
"Little Penny": A pip-squeak at 10 inches tall. Cool terra cotta color.
All five have strong foliage, a long flowering season, superior disease resistance, and high pollinator appeal. What's not to like?
And, just so you can impress your friends, they were also extremely "floriferous."