BOTH GARDENERS and their plants have to be more resilient than ever these days in our changing climate it seems. At the High Line in New York City, one of the best-known naturalistic gardens anywhere, that’s especially so, since it’s built on the preposterous site of a former rail line, 30 feet above street level, meaning a plant must be an exceptional performer to make the grade. Richard Hayden, the High Line’s Senior Director of Horticulture, talked to me about the plants that excel in different extremes of moisture, for instance, or in shade, or offer the most ecologically, and about how the team is using certain species to create weed-suppressing living green mulch, and also shifting their thinking about gardens as ecological communities rather than a collection of plants. Richard joined the High Line four years ago to lead the team that manages the mile-and-a-half-long stretch of gardens, with two new areas set to open this year. Also: On Saturday, May 30, the High Line is holding its first-ever plant sale with 39 different species the team has propagated from the garden—some of those top performers, that play key roles in making the High Line work aesthetically and ecologically. […]