Sustainable Gardening

A woman is engaging in sustainable gardening at a Socal garden center.

Written by David S.

There are many layers of soil. In traditional gardening, the focus has been on topsoil, which is the second layer of soil. With sustainable gardening, the focus includes the two top layers of soil:

  1. The humus layer — is a natural mulch layer, such as from fallen leaves.
  2. The topsoil layer — is the broken down, nutrient-rich humus layer. 

In this article, we focus on:

  • These two layers of soil
  • What their makeup is
  • How to amend them
  • And the benefits of caring for them. 

Soil Biota — A living legacy 

Biota refers to the animal and plant life within a specific location. In the case of sustainable gardening, that location is the top two layers of soil. By animal life, we mean organisms such as earthworms, and by plant life, we stretch the boundaries of scientific definition to include organisms such as fungi. 

Within healthy soil, there is a balance of beneficial and non-beneficial organisms. That balance is part of what we care for when we practice sustainable gardening. The goal here is to build healthy soil because within healthy soil are all the micro-organisms that help plants grow. These include:

  • Those creatures that bind nitrogen to the ground so that plants can use it. 
  • Aeration experts, such as earthworms 
  • Warriors, such as nematodes that takedown plant harming organisms
  • Connectors, such as mycorrhizal fungi. 

These organisms are the keystones of healthy soil. They turn compost and leaf litter into usable nutrients that plants use. They keep the soil light and airy, so garden plants do not suffer root disease. They help to keep the soil aerobic and oxygenated. They may also allow certain plants to uptake nutrients, and they keep plant-destroying organism populations small. These are all some benefits of healthy soil and healthy populations of soil biota. 

The Humus Layer 

The very top layer of soil is called the humus layer. In old forests, the humus layer is many feet deep. In arid deserts, the humus soil may not even be present or so thin as to be barely noticeable. When we garden, we have control over both the humus layer and the topsoil layer. One of the easiest ways to improve the humus layer is to add mulch to your garden. Mulch can include:

  • Compost — commercially produced or home-produced
  • Certain types of wood chips
  • Grass clippings
  • Plant clipping — which we call chop-and-drop composting.
  • Aggregates, such as perlite or vermiculite 
  • Water absorbing material such as coconut coir.

The Role of the Humus Layer

The humus layer gradually breaks down and becomes topsoil. That process can take years or just a few months. It is the layer of soil that defines how nutrient-rich topsoil is. In a desert setting, the earth is generally very poor. The plants that live there struggle to survive for lack of water and lack of nutrients. 

On the other hand, If you’ve walked through a forest, you begin to notice all the plant life: ferns, flowers, understory trees, shrubs, grasses, etc. Those plants grow because the forest supports that life from its healthy production of humus that accumulates on the ground. Humus includes fallen leaves, branches, dead plants, and the beneficial aspects of animal feces. Those are all things that makeup part of the humus layer of a forest. In the desert, much of those items are missing. Those stark comparisons show us how vital humus is to soil health. 

Another aspect of the humus layer is water retention. A healthy humus layer helps prevent or slow down the evaporation of water from the soil. In short, it helps keep the soil moist for longer. That process is suitable for your plants and better for the soil biota, which prefers moist soil to dry clays — Forest vs. desert. 

What You Can Do to Address and Amend the Humus Layer in Your Garden

Mulch is an easy Fix — One of the critical components of improving soil heal is mulch. Bagged wood chips, specialty mulches, coconut coir, and even small stones. All these top dressings break down except for the stones, and as they do, they improve the nutrient load in the soil. 

Compost is also a good fix — Generally, we talk about compost as a soil amendment, which is an excellent amendment. In this case, we are discussing A top dressing. You can use bagged compost or several other options. Those include:

  • Lawn clippings spread them thinly, so they do not become a habitat for garden pests, such as slugs. 
  • Vegetable cuttings — There is a method of mulching using vegetable clippings called Chop-and-Drop. When you take out old plants, chop them up into small pieces and spread them around the soil where newer plants grow. 
  • Bagged Compost is mainly broken down, but it will leach nutrients into the topsoil and down to the plant roots. Good bagged compost should be organic. It can also have organic biota, which will help to kickstart the nutrient cycle. 
  • Coconut Coir — is the fibrous fringe of ground-up coconut shells. It is a beautiful soil amendment as it helps to let the soil breathe and hold water simultaneously. As a top dressing, coconut coir is excellent. It will break down slowly and become topsoil. As it does, add more.
  • Fresh Compost — Some gardeners add fresh compost to the tops of garden beds, especially if those beds are empty. It is essential to realize that fresh compost can become a pest magnet and become anaerobic — very smelly and potentially toxic. 

Why Humus Is Important 

The humus layer is essential for many reasons. Many of those are listed above; however, the last important point is this: The humus layer helps keep beneficial microbes near the soil’s surface. That is a significant boost to plant health. The humus layer holds water in the earth so that those organisms can thrive. Healthy soil should be moist, not wet or soggy. It should drain. As water passes through the earth, it draws down new supplies of nutrients from the humus layer. 

Healthy soil is the first step in sustainable gardening. As you build soil health, the garden improves. The more your garden improves, the bigger the crop yields become. If you are gardening in a small space, larger crop yields are essential. 

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