The what and why of organic soil amendments and soil food

What’s the secret to rich, productive soil? Food! Soil has to eat…just like us and every other living thing out there. Our most important garden job is feeding the soil. When we do this, the microbes, fungi, worms, and other critters in the soil ecosystem do what they do best: eat and procreate. In the process, they take care of plant nutrition, pest control, water conservation, and tillage. Well-fed and active microbes lead to a garden that feeds you, naturally.

But let’s back up a minute – why feed soils at all? In nature, soils feed themselves. Soil doesn’t start and stop at the ground level. Soil is intricately connected to the plants growing in and up out of it. Soil extends to the highest sun-reaching leaves and the deepest seeking root tips. Soil is the leaves that fall from the trees to decompose and feed microbes; it is the dead roots that stay in the ground as carbon reserves.

Soil doesn’t start and stop at the ground level. Soil extends to the highest sun-reaching leaves and the deepest seeking root tips. Soil is the leaves that fall from the trees to decompose and feed microbes; it is the dead roots that stay in the ground as carbon reserves.

In other words, soil grows its own food. Nature doesn’t rake away fallen leaves or rip up plant roots. Nature leaves grass thatch on the ground to create productive prairie soils. Occasionally, a fire may burn through to clean out debris, but it leaves nutrient-rich ash behind to fertilize and refresh.

A leguminous nitrogen fixer in an Indonesian forest
A leguminous shrub in a multi-layered forest feeds the soil with nitrogen from litter fall and roots.

When we garden, of course, we always remove something from the soil – our harvest, weeds, prunings, and clippings. Our first step, then, in feeding the soil starts with following nature’s lead. If there’s not a good reason to remove soil food (in this case, plant litter), I leave it in place to decompose and return to the soil.

To make up for the rest, I use organic soil amendments to feed the soil. What are organic soil amendments? Organic matter refers to anything that was once alive. When we add it to the soil, it breaks down into carbon, nitrogen, and other building blocks that feed and fuel the bustling activity below ground. As soil organisms digest and transform the soil food, they release nutrients plants need to grow. See more on this in my next post, which clarifies the difference between using fertilizers and amendments for soil fertility.

Because organic amendments encourage organism activity, they are also used to improve soil condition. Soil condition is the general texture, structure, and feel of a soil. How easy it is to dig; how well it holds water; how it crumbles in your hand – these are all aspects of soil condition. As organisms burrow, secrete, and excrete they soften and aerate soils, while creating the crumbly texture of gardening dreams.

So that’s the long and short of it. Gardens need soil. Soil needs food. The closer we can get to nature, the easier our job becomes. Otherwise, we need to add organic amendments to feed and nurture an active living soil. In the process, we build up a pool of organic matter and create bustling cities of soil organisms that fertilize our plants, create soft crumbly soil condition, hold water, drain well, and keep pest and disease in check. Remember the fundamental rule: we all have to eat.

The next few posts will explore the wealth of soil amendments available, how to judge amendment quality, and how to choose the best soil food for your garden.

Feed the Soil, Part 1: What are Organic Soil Amendments
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