|The same rules that create impact and drama in art can be applied to perennial planting.
My last post set up my proposition that perennials and grasses—the most dynamic plants a gardener can use—ought to not only be used more often, but used in as a larger percentage of our built landscapes. It’s time to liberate perennials from the confines of the British border and embrace a new aesthetic inspired by the patterns and palettes of our native vegetation.
First, let’s understand the context we’re discussing. Perennials in a landscape setting (parks, civic landscapes, large residential) are inherently different than a flower border. They are larger in area, typically set farther away from the viewer, and are not gardened as intensively. So the rules of composition must address this context.
|Larger massings of sedges and perennials in a biofiltration garden for an office park. The lines between the species create a pleasing composition. Design by Ed Hamm for Rhodeside & Harwell. Photo by Thomas Rainer.
The European ‘New Wave’ style made popular by designers like Piet Oudolf, Noel Kingsbury, Michael King, and other celebrated designers tends to interplant perennials in smaller clusters to create highly textured tapestries. I am personally a huge fan of this look, particularly to see it executed on large public projects like the Highline and Lurie Garden in Chicago (even Oudolf masses plants together for effect). These designers use repetition rather than massing to give their compositions visual coherence. However, in my experience, the main drawback of a mixed meadow approach is that it requires quite a bit of maintenance, particularly in the heat and humidity of the eastern U.S.
Massing reduces maintenance. By placing plants of the same species together, you group them by their cultural requirements. Everything within that block needs the same care. It also makes weeds much easier to identify. In highly mixed plantings, identifying a weed from a young perennial or grass requires a trained gardener—a luxury not available in most landscape settings. Massing also makes it easy to re-plant if a perennial dies or struggles. Every project I’ve ever worked on required re-planting anywhere from 3-10% after the first year or two. With large masses, it’s very clear what needs to be replanted.
|A nicely interplanted moment, but with five species in just a few square feet, the perennials are already competing for light and nutrients. To keep this composition together would require quite a bit of maintenance.
Massing plants of the same species together also reduces competition between perennials. Any time you mix species, the plants compete for light, water, and nutrients. All of my early experiments with interplanting perennials went poorly as one plant often “ate” another. The composition grew together, the more aggressive plants eliminated their more demure counterparts, and the end result was a total mess. On one project where I interplanted about ½ acre of perennials, I went back a year after it was installed and had to un-interplant the entire garden. The garden had grown together in this awful mess. Anything that was mixed together was pulled out and separated. The correction worked. I’ve visited it several times in year two, three, and four. The masses are more readable, the maintenance staff can easily identify weed from desired plan, and the garden is more stable.
Since then I’ve had a good bit more success with interplanting perennials, but it requires much more planning, horticultural knowledge, and care with plant selection than I initially understood. I’ll discuss some simpler strategies for interplanting later. Even though I interplant quite a bit now, it is still within the context of larger masses.
|Two images of a garden designed by Wolfgang Oehme that feature large
perennial masses appropriately scaled for the residential setting.