Underfoot, Lofty: Good Soil for Healthy Plants (P. 1/3)

Let’s talk about soil. I made this pitch last spring and since then, I’ve learned more about soil and noticed a lot of interest in it in popular media. (See links below.) So I’m recharging my appeal this year: before we get into our gardens this spring with shovels, stop and consider the soil in your plot and how to protect and make good use of it.

Organic

A simple rule in our organic community garden is that we don’t use any agricultural chemicals. This one’s easy. We all know that products such as Roundup and Sevin aren’t healthy for us or the environment in many ways.

But organic gardening is more fundamentally about supporting nature and working with it. With regard to our soil, even the act of digging into it can mess up its natural beneficial processes. In some ways, less is more. Stop disrupting your soil, and it will thrive and work better for you.

Home Soil

Last fall when I dug a shallow trench to plant my garlic, I felt bad about displacing a handful of earthworms. Those critters were just the obvious living organisms in my garden. A teaspoon of good quality soil is populated with more microorganisms than people on earth. That’s billions of algae, fungi, bacteria, yeasts, protozoa, nematodes, and more. Scientists are only beginning to understand the complex ecosystems in soil and how they support plant life.

Here’s a simplified description of the relationship between your plants and microbes:

  • Plants take in carbon dioxide and through photosynthesis, use the carbon atoms to form sugars.
  • Some sugars are released into the soil through the plants’ roots, providing food for microbes.
  • These microbes, in turn, provide important nutrients right to the root zone of the plant.

Microbes act like home delivery food service. Sounds good, right? Here’s another point to understand: good soil with organic matter holds together in small clumps (aggregates) separated by open pores. Microbes thrive in this kind of environment; in fact, they depend on good soil structure for critical functions. Taking a shovel to it is like bulldozing their natural habitat. And destroying their home means your plants are going to be deprived of the little guys that nurture them. Your plants themselves like good soil structure for other reasons, too.

Soil Care

How can you tell if your soil has good aggregation? A handful of well-aggregated soil has the pebbled texture of cottage cheese. Soil that is poorly aggregated, in contrast, doesn’t hold together at all, or if you gently squeeze it, forms into larger chunks that don’t crumble nicely into pea-sized pieces.

Other bad consequences come from churning up your soil. For example, “tilling soil causes pore spaces to collapse and seal over, causing more rain to run off than sink in.” Your plants aren’t getting that water and worse, water run-off carries away your garden soil. Tilled soil is also lower in organic matter.

I like this description, relayed by Sharon Gensler, the Soil Carbon Outreach Coordinator at NOFA/Mass. “Poor soil is like a mound of flour, which sheds water poured on top rather than absorbing it. On the other hand, water poured over a stack of sliced bread is easily and quickly absorbed. The bread has crumb and texture, with many pours available to absorb and retain the moisture, while the flour is dense with very little porous space for absorption of air or water.”

Last summer, I took over a plot that another gardener couldn’t use. The plot had grown

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Once I pulled all of the purslane from this garden, water pooled on the surface and ran off rather than being absorbed by the soil.

“weedy”  with purslane (an edible plant, though not my favorite), so I set about clearing the entire plot. My thinking went like this: I’d clear the purslane so it wouldn’t compete with my garden plants for water and nutrients, and then I would cover any bare areas with compost and mulch to protect and build the soil.

Once all of those plants were cleared, however, I found I was left with dry, dusty soil that didn’t hold water well. Have you ever had a problem with hydrophobic soil? You might have experienced it when you let a flower pot filled with a peat-based mix dry out. No matter how much I watered the cleared garden, the soil seemed to repel, rather than absorb the water.

I went ahead as planned and covered the soil with compost and wood mulch–which helped with the watering problem, eventually–but I would not have had to remediate so extensively if I had selectively left some of that purslane in place. In many cases, a living root is better than compost and mulch. To be clear, I’m not advocating for letting any weed run rampant in the garden; certainly some weeds will outcompete garden plants. But in this case, I should have thought of that purslane itself as a garden plant–not only because it was edible, but also because it would have been a good friend to my garden, protecting the soil from erosion, supporting microbial life, and helping to retain water.

Bottom Line?

Start with soil! Make friends with the billions of organisms living underfoot, and they’ll do a lot of heavy lifting for you and your plants. Setting the shovel aside is just one way to keep your soil zoo happy. I’ll talk about what I’ve learned about no-dig and other soil-building methods, but up next in Part 2: Good Soil for a Healthy Planet.


For More Info…

From Green America, understanding the complexities of soil.

Interesting fact sheet from the USDA on soil health.

The Zoo Beneath Our Feet, from the Washington Post.

What is humus? From National Geographic.

Got worms? Earthworms can be an indicator of soil health. From MSU Extension.

How to Turn Dirt Into Soil From Yes! magazine, home gardeners share their experiences.

A deeper dive into soil aggregation. From the Soil System Sciences (SSS) Division of the European Geosciences Union(EGU).

 

 

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