Cut Greens (and the Roman Connection)

a pile of cut greens (mostly pine branches) discarded by the street

“One man’s trash is another man’s treasure,” or as Lucretius put it back in Roman times, “What is food to one would be bitter poison to others.” (Ut quod ali cibus est aliis fuat acre venenum, On the Nature of Things, Book IV, line 637) That’s practically the translation of the Japanese version: “Some insects eat water pepper and like it,” or, “there are even bugs that eat knotweed,” an expression that refers to the plant Persicaria hydropiper and the fact that livestock won’t touch it. Then there is the keen principle on perspective coined by Rufus Miles, Jr. in the late 1940s: “Where you stand depends on where you sit.” If you’re a gardener, you already know your nature is to view the world with eyes that differ from the rest!

a pile of cut greens (mostly pine branches) discarded near the road as cars drive bySome people still observe old pagan customs such as decorating for the winter solstice. After the holiday ends, the cut evergreens they discard still have value. It’s just not decorative value any longer: it’s functional.

Experienced gardeners know some plants benefit from a light winter mulch, the kind cut branches can provide. These plants include strawberries, heather, peonies, and helianthemum, but overall, most perennials in general. Winter cover like this can make the biggest difference not in our coldest areas, but in places like Missouri and Arkansas where it gets cold without snow on the ground.

Gardeners also know soil left bare in the winter can erode, or weeds can start to grow there since most weed seeds need exposure to light. So that bed where you had petunias, geraniums, and cannas is best put to bed if you didn’t install hardy annuals such as alyssum, calendula, forget-me-not, wallflower, ornamental kale, snapdragons, and pansies.

Since strawberries and petunias prosper in slightly acidic soil, you might believe this branch cover for winter is just what they need in more than one way. When it’s time to remove the cover, which is early spring, some people may put the cut evergreen branches under and around acid-loving trees and shrubs such as holly, gardenia, boxwood, magnolia, blueberry, azalea, and rhododendron, believing the acidity this material provides (and other factors) will help them flourish.

There seems to be some contention as to whether pine needles in particular, or evergreen branches in general, would lower soil pH. Under some conditions, the answer appears to be no. In other conditions, the answer is yes, but on a long time scale: over decades, not years. Other types of leaves can give quick results. But the dominant factor–surprise!–is how much calcium a mulch has, not whether it is leaves or needles. Clayton Butterly has done a lot of research looking into how soil pH can be affected by amendments and crop residues.

a wintry scene of a farm, with a fence, pond, and buildings in the distance

Phil Nauta warns against holding a simplified view of pH as merely a number to get right. He reminds us that pH is important primarily because it indicates what nutrients may be available–and may not. A study done in England in 2009 has shown that soil microbes vary with pH, so soils that differ support different communities of microbes, which in turn affect plant growth. If all this seems confusing, the point is that a holistic view of soil is more appropriate to a gardener than a simple, reduced one, and the best perspective considers the many nutrients soil can provide and the many microorganisms that can live there.

For more about mulches and soil pH, see here.
For more about soil itself, see here.

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