‘Tis the season of garden seminars. Recently I participated in a thought-provoking one-day seminar on the theme of bringing nature into our cities. I spoke about hellstrip gardens, but a couple of the other speakers addressed larger-scale landscapes. After seeing their photos and hearing about so many projects that are underway or have already been developed in different cities around the world, I left feeling hopeful about the direction of urban design in this country and globally.


View of the High Line, from the book Hellstrip Gardening. Photo by Josh McCullough.

A highlight was hearing Patrick Cullina speak about his experience designing and managing the acclaimed High Line Park in New York City, a conversion of an old elevated rail line into a public “promenade” with naturalistic landscaping, plenty of paths, and places to hang out in settings from secluded to central.

While showing many photos of the High Line, including some “before” and “during” ones, Cullina made a persuasive argument for the benefits of landscaping post-industrial sites (such as abandoned railways). These sites can simultaneously reference the city’s history and provide safe corridors for wildlife and pedestrians, connect neighborhoods, open up new views across and within a city (like the views of the Hudson River and down the length of major streets from above that the High Line offers), add habitat for both plants and animals, showcase public art, inject seasonal change into urban areas, be gathering spots and stages for impromptu and other live performances, help urban dwellers connect with nature, improve the local economy through tourism and by raising property values and decreasing crime, and provide large-scale space for children that is contained and separated from car traffic. Whew! Talk about multiple benefits.

The High Line has received over 4 million visitors since the project’s first phase opened in 2009. The park has already become an icon in that city of so many iconic places. It hosts public art, live performances, parties, work sessions, food vendors, classes, and tours. It includes special play areas for kids. For a sampling of what goes on there, check out this “year in review” post from 2014 at the Friends of the High Line blog.

(And for you avid gardeners who wonder about these details, we learned that the garden areas of the park have an average of 18 inches of soil depth. Though the plantings were inspired by the vegetation that grew up during its abandonment, the entire site had to be structurally fortified and the hardscape constructed before the soil and plants were brought in. Prairie plants and deciduous woody plants dominate to provide maximum seasonal variation. Seedlings rather than named varieties were used to encourage natural variation of colors and growth habits. In other words, it’s a naturalistic design in a wholly manmade environment.)

Another notable talk was the overview of green roof designs in many different countries presented by Karla Dakin, one of the authors of The Professional Design Guide to Green Roofs (Timber Press, 2013).

The science of designing green roofs has made huge strides. Simple designs featuring  varieties of sedums have given way to broad experimenting with native and other climate-appropriate plants.


A sedum-dominated green roof at the 4-H Children’s Garden in Michigan.

Counter-intuitively, roof gardens aren’t necessarily xeriscape environments. In areas with enough rainfall, they can be watered until established then left unirrigated, but in fire-prone regions they may require monthly watering to keep the plants from going dormant and dry.

But in exchange for water spent on them, green roofs do provide significant benefits in urban areas. They can mitigate urban heat by 40 to 60 degrees! They also process stormwater and filter air pollutants, making cities healthier for us all.

Dakin pointed out that roof gardens can create communities too — both as physical gathering spaces and as projects where private citizens and public organizations work together. Like the High Line, a public roof garden gets people out of car-dominated spaces and gives them a safer open space in which to gather and linger. And like other major public projects including the High Line, a substantial roof garden requires the kind of funding that can only come from cooperation between several entities (or a really excited philanthropist).

Sean Hogan, plant explorer, designer, and proprietor of Cistus Nursery in Oregon, spoke on using native western plants in green roof design. He said diversity is important to make green roofs more self-sustaining and to strengthen the ecosystem services they provide. His average green roof project contains over 100 species.

If, like me, you are curious to learn more about these ultra-urban landscapes, the Green Roofs and Walls of the World Virtual Summit is happening THIS WEEK. Check out the list of presenters, plus there will be live Q&A sessions and many vendors, all accessible from the comfort of your own home and computer.

How the heck does this virtual event work? Here’s a little explanatory video.