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Report from Soil Biology School

by John Rice

One of the things I love about winter is that I get to meet with scientists, professors, and researchers and learn more about the ever-changing landscaping world. To use the tools, the microscopes, etc. that they have and to see the microscopic world is just fascinating.

One of the things I am consistently reminded of in the studies and in my professional experience is: don’t routinely fertilize your shrubs and trees every year. Do not do it. Here’s why:

If you do fertilize every year, you will almost always have to spray the fertilized plant material for pests and disease later that year. It is vicious cycle. Fertilizing a plant stimulates it to grow too fast, weakening the plant’s natural defenses to pests and disease. The fast growing plants cannot protect themselves after being stressed from over-growing; the fertilizer weakens rather than strengthens them. (Think athletes on steroids.) Fast growth and weakened plants means you end up having to spray the plants for the disease and pests that many healthy plants could have fought off on their own.

The bottom line? You almost never want to fertilize the roots of your plants, especially with a liquid fertilizer.

The inside details? When you fertilize, the roots of your plants with a rapid feed fertilizer the plants grow fast and look happy – usually very happy, with a nice flush of growth. But, the roots don’t keep pace. Instead, the roots take up the fertilizer that we have given them and get “lazy,” waiting for more fertilizer. Also, the root fertilizers have salts in them that leach the natural nutrients out of the soil. Consequently, the soil around the roots becomes more infertile as time goes on, and lo and behold, you need more fertilizer. Finally, worms don’t like the corrosiveness of salts so they often leave or die. In this way, you lose the benefit of all the castings and aeration that worms provide.

Many relationships existbetween soil food web plants, organic matter, and birds and mammals. Image courtesy of USDA Natural Resources Conservation Service.

Many relationships existbetween soil food web plants, organic matter, and birds and mammals. Image courtesy of USDA Natural Resources Conservation Service.

Building Your Soil

What you do want to “fertilize” is not the plant, but the soil. More correctly stated you want to build your soils so that the soil biology is healthy. You do this by setting up practices that build your soils naturally and with as few inputs as necessary. The foundation for most growing things is the soil. How can that soil be as healthy as possible?

Provide organic matter: Life in your soil is all connected by a food web. Organic matter is at the bottom of the soil food web and contains the bacteria and fungi which are attracted to and consume plant root exudates. Fifty percent of the energy a plant puts into its roots is released into the soil as exudates. These released exudates feed the bacteria and fungi around the roots. This results in beneficial microbes creating a type of shield around the roots, protecting the plant from disease. So a plant inherently is trying to protect itself. Pretty cool.

When your plant grows at a healthy pace and is attacked by an eating or sucking insect, the plant can send toxins into its leaves to ward off the pest attack. When is roots are healthy they also send out pheromones to attract bugs it needs help from; bugs that will feed on the pest attacking it. Amazing what is going on that we don’t know.

In turn, the bacteria and fungi attract and are eaten by bigger microbes, the protozoa and nematodes. Anything they don’t need is excreted as wastes, which the plants roots readily take up as nutrients. All this takes place in the rizosphere, the site of root nutrient absorption.

The protozoa and nematodes that feasted on the bacteria and fungi attracted by the plant exudates are, in turn, eaten by the arthropods (e.g., spiders and insects). Soil arthropods eat each other and themselves, and are food for birds, snakes, and other animals. These arthropods are what eat any ticks that go in your lawn.

Simply put, the soil is one big fast food restaurant. Organic matter feeds this system and keeps your soil healthy. Compost, decaying plant material, some mulches, and compost tea are all examples of organic matter.

Lawns and Soil

How does this apply to lawns?

Typical lawn roots will go 24-36” inches deep if they have good healthy loam to grow in. That is not a misprint. When you fertilize lawns synthetically the roots grow about 2”-3” and wait for the next fertilizer application. How much do you think a strong, healthy root system could save you on your water bill?

Thirty-nine percent of water use is for landscaping, much of it for lawns. How much could you save on water if your lawn roots were just 6+ inches deep? If you can live with 5% weed pressure, you can have an organic lawn. Do you remember when you were kid and robins use to run around your lawn picking up worms? An organic lawn can bring that back to your property

Compost Tea? What’s That?

Compost tea is a water extract of compost. Compared with compost, compost tea has additional ingredients such as humates, kelp, and molasses that are often added as food for microbes in the tea and become additional nutrients to the soil. Compost tea has millions and sometimes billions of beneficial microorganisms in it that encourage plant growth.

Compost tea is not the magic bullet many people wanted it to be. It cannot bring back dead soil. Over time, however, it is a useful tool in building healthy soil. I have been testing it on my property and am very encouraged by the results.

Compost tea will typically be either bacteria or fungi dominant depending on what it is being used for. The ratio between bacteria and fungi is the most important thing to know about your soil. Once you know what the ratio is in your beds, you can adjust it with the right nutrients so that your plant are healthy and happy.

After a winter of workshops and education, I’m ready to apply all that knowledge in the landscape.

About the Author

John Rice owns Inspirational Gardens, an organic and ecologically based landscaping company located in Acton, MA. John may be reached at