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Sunday, October 9, 2016

Banking on living soil

Have you been hearing recently about your gut’s microbiome? All of a sudden we’re recognizing the importance of microorganisms that live in our intestines for maintaining good digestion and general health.

    Similarly, we’ve recently focused on the importance of living things in soil. Instead of noticing just physical properties—sandy versus clay soil—and chemical aspects—acidity and concentrations of minerals—we’re zooming in on the rich community of organisms that live in and maintain soil. Without them, our plants wouldn’t be able to grow.

Plants depend on soil organisms to make water and nutrients available

    Bacteria, algae, fungi, nematodes, and larger animals such as earthworms and insects all help create and maintain healthy soil and build the pore spaces needed to hold water and air. Bob Schindelbeck of Cornell’s Department of Soil and Crop Science recently provided a useful overview of what these soil inhabitants are up to and how to encourage them in Fine Gardening. I loved his characterization of soil organisms as “your ‘underground herd.’” This is a new perspective, thinking of soil inhabitants as animals on our team that are worth fostering.

A large member of the herd

    Because the top few inches of the soil are full of active organisms breaking down organic material and digging tunnels, cooperating with plant roots to create a useful architecture, it’s better not to till soil or even turn it with a spade when you don’t have to. Instead, to add organic material you can just layer compost and manure on top of the soil and let the “herd” mix it in. 

An interpretive sign along a nature walk tells it all
To help them do their job, it’s good to avoid compacting garden soil by walking on it, which can collapse the pore spaces, especially when the ground is wet. I have to admit that I haven’t put enough paths or stepping stones in my garden, wanting every inch for plants. I’m going to work on that in future.

More paths would keep me from damaging soil structure
    Another living component of soil that I didn’t know about until recently is the “seed bank,” the seeds lying in the soil awaiting the right conditions for germination. Although some will germinate as soon as there's enough moisture, others stay dormant for many years.

Lotus seeds can stay viable in pond soil for 1200 years

When I used to turn my vegetable garden’s soil every spring, I was bringing those stored seeds to the surface.

Goldenrod seeds were waiting in the soil for a good growing opportunity

    I’m still seeing the results of a deposit I made to the seed bank. About ten years ago, I planted tall verbena (Verbena bonariensis), which produces a vast harvest of seeds. A few of them sprout every spring, fewer now that I’ve stopped turning the soil.

Tall verbena seeds last several years in the ground

    Another withdrawal from the seed bank is happening without my intervention. For the past few years I’ve seen heart-leaved aster (Symphotrichum cordifolium) sprouting all around the yard, even more this year. 

Dormant seeds of heart-leaved aster have sprouted around the garden

This is a species that grows in dry, sandy, and compacted soil. It’s out-competing other perennials that are more sensitive to drought and my heavy feet. Bees are foraging among the delicate flowers, so I’m glad this native aster banked its seeds.

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