Intermingling and the Aesthetics of Ecology

Is intermingling really more ecological? Or just the stylized look of ecology?

This summer the Highline had its four year anniversary. Perhaps the greatest testament to its massive success is the extent to which the strategy of “intermingling” plants—as opposed to solid massings of single species—has been accepted as a new ecological best practice. The traditional horticultural practice of massing plants together in solid blocks is now seen as static and old school. Mixing plants into carefully woven tapestries is the expression of the ecological zeitgeist.  Almost all of the world’s planting avant-garde (Oudolf, Kingsbury, Sarah Price, James Hitchmough and Nigel Dunnett, Cassian Schmidt, Dan Pearson, Roy Diblik) have projects that celebrate this mixed style.

Noel Kingsbury and Piet Oudolf’s latest book, Planting: A New Perspective, is a celebration of rise of a more intermingled style. Kingsbury has long been an advocate of this mixed planting style, but this latest book positions intermingling as a part of a new international movement. Intermingling is seen not only as a new design trend, but as a way of creating better ecological function. In a recent article in the journal Topos, Kingsbury writes:

Creating intermingling plant combinations, whether aesthetically driven or strictly functional, creates an ecology. In a conventional horticultural planting, plants are discouraged from interacting, but when they do, ecology starts to take over. "Trends in Planting Design." Topos, 83, 2013

Statements like these raise several questions in my mind: is intermingling really more ecological? Or is it just an aesthetic that imitates ecology? And what about function? Does intermingling plants result in more stable, lower maintenance plantings? Or does it require more intensive gardening to maintain it? 

My own experiments with intermingling have been eye-opening. I wanted to record a few of my own thoughts about intermingling and also hear your reactions to this rising trend.

Perennials to Interplant in Grasses

Of all my plant obsessions, herbaceous plants are among my favorites. Several years back, I remember walking through the woods with a colleague, a tree expert. After several hundred yards, we laughed at each other. He was always looking up at the canopies, and I was always looking down at the ground—scanning the forest floor for herbaceous plants. It is my perpetual posture: head down, scanning right to left.

Amorpha canescens

As a perpetual ground-scanner, I’ve recently had a revelation about the way many perennials and grasses are meant to grow together. This revelation has influenced the way I design.

It’s actually quite simple: many perennials from meadow/prairie ecosystems have evolved to grow within a matrix of grasses. While that is not a particularly ground-breaking concept, it does challenge the way many perennial gardeners arrange their plants. Most perennial gardens focus heavily on forbs (blooming perennials) that are scattered one by one in planting beds. Grasses, if used at all, tend to be added as specimens or accents. But if you consider the way most meadow perennials grow, this ratio should be reversed. The grasses are meant to be the dominant plants with forbs emerging through this matrix.

Consider the morphology of an Echinacea (Cone Flower). Echinaceas typically have low basal foliage and tall spindly stems which support the flowers. This very structure is designed to help the plant grow out of a lot of grasses. The low foliage first emerges in late spring before the warm season grasses emerge, grabbing sunlight to ready the plant for its flowering. Once the grasses put on their height, the Cone Flower sends up its flowers on delicate stalks. The grasses support the flower (like a stake). If you’ve ever had perennials flop over, it may be because it is missing its support system.

As a gardener or designer, this does not mean that your perennial gardens need to be mostly grasses. It does, however, provide a real opportunity for people interested in designing with ornamental grasses. I love the look of large masses of ornamental grasses in a landscape. They are easy, low maintenance, have a long season of interest (particularly in winter), and add a wonderful looseness and spontaneity to a landscape.

Dalea purpurea growing in grasses