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Plant Evaluation Notes

PEN: from the Green Roof

The first study of its kind in the nation
Green roofs. In plant science (and gardening), the new frontier is overhead rather than underfoot.

On the 16,000-square-foot Green Roof Garden at the Daniel F. and Ada L. Rice Plant Conservation Science Center, associate scientist and plant evaluation manager Richard Hawke has conducted a grand experiment, the first of its kind in the United States. In a five-year study of more than 40,000 plants installed in three different soil depths (4-inch, 6-inch, and 8-inch), Hawke evaluated plant performance in this most challenging of growing environments. (The rooftop is beautiful—check it out in our video.)

The results are in. Of 216 taxa tested on the roof, nine top-performing plants have been rated “five-star,” with an additional 69 plants earning a “four-star” rating. Which plants proved themselves hardiest, most adaptable, most pest-resistant, and still beautiful? You may recognize some of the top performers (creeping phlox, prairie dropseed) on our Smug Mug gallery here.

Hawke’s PEN (Plant Evaluation Notes) give an extraordinary overview of the plants and the process of evaluation in this unusual environment. This is Hawke’s 38th plant evaluation study—each report is a rich resource of information, with comparisons of beloved garden plants like shrub roses, geraniums, clematis, coral bells, and so many others. The Plant Evaluation web page lists all of his work to date for our USDA zone 5 climate zone.

Share our infographic on the top nine rooftop plants with the gardeners, breeders, nursery growers, and plant buffs you know!