Lettuce Consider Garden Diversity

As spring's passionate climax approaches, I'm thinking about how much diversity does a garden need?

My mind drifts back to 1982. As I wrote my rough proposal for a book on edible landscaping while at Oyster Bay, NY. (Designing and Maintaining Your Edible Landscape – Naturally; 1986, Metamorphic Press.) I gazed across a well-clipped estate lawn to an recently-abandoned tennis court.

After just a few seasons of neglect, every fissure in the asphalt had been filled with grasses and a wealth of herbaceous weeds. More remarkably, well-anchored saplings of the mimosa tree (Albizia julibrissan) were already several feet high and beginning to heave the tarmac. In less than a decade, those mimosas' will have completely cloaked the court's rubble with a prosperous, verdant forest. How quickly nature can reclaim what we pretend to husband or nurture. All the human effort we put into cultivated gardens is dwarfed by even the casual momentum of nature. Once untended, even the most environmentally-kosher garden soon returns to nature's bosom. Buried within this steady, powerful momentum are the seeds of nature's renewal—which are more powerful than any human garden.

I visited the site of Allan Chadwick’s Covelo, CA garden just a few years after it was abandoned. Allan Chadwick was the guru of French-intensive, biodynamic gardening. Apprentices flocked from around the world to learn from this strident and demanding teacher. Yet, the garden was a riot of weeds. The most prevalent were lemon balm and comfrey. Proof that their composting was not hot enough to kill all garden seeds. The comfrey was (and probably still is) a biological nightmare. Just a tiny piece of root can sprout become a huge plant in matter of a few years. Probably the apprentices had skimmed bed of comfrey for compost, but skimmed deep enough to gather the crowns of the plants. I used to plant comfrey, some 38 years ago during the early days of my infatuation with intercropping, companion planting, and the silica-enhanced comfrey At the time I assumed that planting it in with vegetables would allow its deep roots to bring up special minerals from deeper places than the vegetables could reach. I regret to this day that the tillage of those gardens spread unwanted comfrey throughout the beds. Now my comfrey is five feet from any tillage, is never watered, and the leaves are cut well above the crown for compost. Yet I have to struggle to remove the roots that have found the moisture of the raised bed with it’s lemon bush. Slow learner I guess. Now, in any design I do for a client there is no comfrey to be found.

A common theme in the sustainable/organic/permaculture world is the premise "diversity equals stability." I wish the continual references to "Diversity", “Climax”, and “Stability” would end. While diversity within an ecosystem allows for a complex interaction between all the elements, plants, animals, and people; it is not a panacea. A “mature, climax” forest is often the model of “stability”. Yet winds knock down trees to open up little meadows to start the whole process again. The edges often have to repeat what lead the forest to have a mixture of trees and other plants. Trees die to be replaced by some of the same progression leading up to a climax.

A climax forest is not always the natural climax. Vernal pools, sand dunes, chaparral, bogs, and other ecosystems thrive without forming a continuous canopy of trees. Too often in gardening books, what appears to be a great way to garden is based on the experience of tropical ecosystems. Using tropical diversity as a model is childlike. While the tropics often have lots of vertically-integrated plants, the temperate American landscape, with its hardwood forests, meadows, and prairies, is less vertically complex and is more adapted to the growth of annual plants than the tropics. More importantly, in the tropics the nutrients are stored above ground in the biomass. Whereas in temperate ecosystem, the nutrients are stored in the soil. Randomly-chosen diversity or complexity doesn't necessarily provide any special benefits.

A good example is the wish that beans climbing corn will feed the corn with nitrogen. However, beans don’t “share” much of their nitrogen nodules with other plants while they're growing. unless they go into severe drought, die, are mowed, grazed, and after tilled under just as blossoming begins. (See page 49 of Roots Demystified, Change Your Gardening Habits to Help Roots Thrive. 2008, Metamorphic Press.) The legume is selfish, it is building up a supply of nitrogen in its rots to move it into the formation of seed. Only then, will the nitrogen become available to other plants. But most of the nitrogen will, by that time, be in the seed, not the foliage or roots. That’s the temperate dynamics. In the tropics, nutrients cycle so fast that even some leaves falling off the older stems of the bean plants rot and release some nitrogen on the surface of the thin layer of soil.

However, in both climates it is well proven that a green manure crop of any number of legumes greatly increases the total amount of nitrogen. Crop rotations where a field or planting bed is left to fallow for a year with legumes also increases nitrogen for the next crop.

But our garden's diversity must be, to our current knowledge, composed of the proper plants. For example, the kudzu vine is theoretically a multipurpose plant with many edible parts and useful fibers. Adding kudzu would be another unit of diversity in your garden. But you better leave town before your neighbors come after you as the kudzu vines entangle everything that's moving slower than 25 miles-per-hour! Kudsu is an extreme example of exotic plant from Japan and China gone wild. Kudzu plants grow rapidly, and may extend to100’ in length at a rate of about one foot per day.

More subtly, you may think twice about nurturing edible lamb's-quarters (often treated as a weed) if you're growing lots of heirloom tomato plants because this "weed" also harbors verticillium wilt—the Achilles Heel of many non-hybrid tomato plants. Too much diversity, or the wrong kind, only promotes that universal dynamic called entropy via chaos.

Too much diversity, or the wrong kind, only promotes the universal dynamics called chaos and entropy. Nonetheless, the organic movement will only continue to grow both literally and figuratively.

In my opinion, gardeners are not as important to nature as we think, nature eventually takes back everything and we should endeavor to stay humble and in our place—relative to the grander scheme of things. As George Carlin so eloquently observed in his 1992 (a man ahead of his time) HBO special: "Save the planet!? Are these fucking people kidding me? There's nothing wrong with the planet that it can't fix. We still haven't learned how to care for one another—and we're gonna save the fucking planet? So, take care of yourself. And take care of somebody else."

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All rights reserved. Copyright 2008


The image is of a kudsu vine covering two tractors and a forest. Photo by Jack Anthony, from
http://www.yahoolavista.com/kudzu/

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