Biodiverse Gardens

A few years back, I attended a garden conference in Ohio where I sat in on a lecture about biodiverse gardens. I had always designed gardens using a broad palette of plants because, well, I like plants. I like both the individual characteristics of specific plants–the arching effect of ornamental grasses, for example–but I also enjoy the way grasses interact and combine with other plants–large leafed plants, for example, to form groupings. Indeed, there are a number of good books published on the art of grouping plants together, books that talk pointedly about “companion plantings” and so forth, which should be of great interest to designers and gardeners alike. It’s a pleasure, or should be, to think about the way plants set one another off in the landscape, or contrast with one another for a desired effect.

Okay, back to the lecture. One of the surprising things I learned during that talk was that, in biodiverse gardens or in nature, plants don’t compete as directly for the same water and minerals in the soil. The reason for this is that when a diverse set of plants live side-by-side, their corresponding root zones have varied depths and spread out in different directions in the subsoil. In this way, many more diverse plants are able to live in the same square-foot area, as opposed to monoculture plantings. Plants are smart, in other words, and survive by forming their own root-spaces in and around neighboring root-spaces. This is one of the reasons why, in a string of shrubs planted in a hedge, like Japanese boxwood or Indian hawthorne, often a few of the shrubs die randomly in the hedge and need to be replaced. Essentially, the monocultural hedge is competing on the same horizontal root-zone with every other plant in the hedge. Eventually, a stronger shrub dominates and thereby weakens its neighbor, especially if they have been planted too close, which is often the case.

Biodiversity is, of course, one of the keys to survival in nature. Plants, like animals, survive in many ways by their intricate relationships and dependencies, in some cases, with other species and their environments. Many more plants are allowed to live in a smaller area in real biodiverse gardens and landscapes, a fact that has been directly linked to reducing harmful plant pathogens in the soil and curbing soil erosion, as well as supporting microbial life and the development of water-storing humus. In the end, biodiversity gardens are healthier and less subject to destruction from diseases and insect infestations. They also become habitats for butterflies, birds, and other wildlife. A visit to the Ladybird Johnson Wildflower Center’s demonstration gardens will drive this point home. In one section, they’ve installed two gardens side-by-side: a biodiverse garden and a monoculture garden. The biodiverse garden is swarming with life: butterflies and bees spring through fall, birds chirping. There’s things in bloom, fragrant plants, etc. The other garden is largely absent of the same life, except for the occasional squirrel passing though it on the way to its next nut.

I just finished reading David Kline’s wonderful book, Great Possessions. It’s an Amish farmer’s journal/essays on simple living, farming and paying attention to the small things. In one essay, “In Praise of Fencerows”, he mourns the loss of the old fences between neighboring fields (Kline lives in Ohio) where birds and animals congregate, nest and burrow, and create whole ecosystems from their daily efforts. Fruit and nut trees, including blackberries, raspberries, wild cherries, hickories, elderberry, sassafras, and mulberry are allowed to grow and cover the fences over time. The birds and animals do all of the “planting” of these gardens on their own, i.e. nothing is “planted” and they provide food for the community as well as enjoyment (Kline is a big birdwatcher, as I am). As farming becomes more and more industrialized, many of these fencerows are being removed and it’s a loss. According to Kline, one of our greatest “possessions” is our duty to preserve nature and its biodiversity, our ability to live together and sustain life. I agree.