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Gardening from Alaska

...soil
by Jeff Lowenfels
by Jeff Lowenfels

email: jeff@gardener.com

Jeff is the Past President of the Garden Writers of America, a columnist with the Anchorage Daily News, Host Alaska Gardens and Supporter of Plant a Row.


June 17, 2007

Starting today in these columns you are as likely to come across hard to spell and difficult to pronounce words like “mycorrhizal,” “hyphae” or “vascular arbuscular,” as you are such familiar horticultural terms as “delphinium”, “sugar snap peas”, “dandelions”, “lawn mowing” or “birch trees.”

Why? Because up until recently we couldn’t see what was happening below ground so we concentrated on above ground activities. While many grew up reading J.R. Rodale’s Organic Gardening and Farming and have always composted and mulched, most didn’t learn anything about soil microbes other than they caused decay and the results were good for gardens.

Things changed for me last fall when a fellow garden writer mentioned he had seen mind-blowing, microscopic images of a single fungus strand protecting a root from a nematode attack, something impossible to record just a few years back.

I found the picture and many more and as a result have been spending an inordinate amount of time reading about recent advances in soil microbiology.

Had you asked me to discuss soil bacteria, fungi or nematodes last year, you would have heard tales of pathogens, mildews, root damage and plant diseases. This was before I was exposed to the science of the Soil Foodweb as it relates to growing plants.

In fact, plants produce exudates, sugars and proteins used to attract and support specific bacteria and fungi to their root zone. These microorganisms, in turn, help the host plants grow and stay healthy.

How, you ask? A teaspoon of good soil contains between 100 million and 1 billion bacteria, each full of carbon and nitrogen and very short lived. Bacteria are food for protozoa and nematodes and they, in turn, are eaten by bigger critters called microarthopods and arthropods, things like mites, beetles, springtails and millipedes. And then there are the worms.

The by-product of each of these meals is a release of nitrogen and other nutrients into the root zone in the exact forms the plant can use. By controlling production of the exudates in the first instance, the plant is charge.

Soil bacteria don’t travel very far, a few millimeters at best, so what they provide a plant is limited to what they eat or produce in the vicinity of the plant. The exudates attract fungi as well, however and like bacteria these also provide nutrition when they die. Some fungi also form a special relationship with the roots and in return for the sugar and protein exudates, they attach to a root and grow far out into the soil and bring back necessary nutrients and water the roots would never reach. Most gardeners don’t know a mere teaspoon of good garden soil contains several yards of fungi hyphae.

Together these fungi and bacteria break down organic matter, retain nutrients, fix nitrogen, bind soil grains into aggregates and, amazingly, form barriers that are impossible for pathogens and root-feeding nematodes to penetrate. In some instances, the beneficial microbes eat the bad ones. One such case recently discovered was reported just last weekend in this paper: Trichoderma atroviride, a soil fungus, attaches to grass roots and eats the fungus that causes snow molds.

Toss in worms, micro arthropods and arthropods and you have a pretty perfect system. This is why no one has to fertilize or apply fungicides to a forest. The natural system is in balance and takes care of itself.

Agricultural activities, yards and gardens by necessity, disrupt this balance. We do all sorts of things to make up for it or to keep it from getting back into balance. Many of these horticultural practices are more Art than Science. Many, like rototilling for example, are based on outdated science. Others, like the use of herbicides and lots of NPK fertilizers, are founded on advertising dollars and chemistry, not common sense and biology.

No longer. Not here. Soil Foodweb advances have a great deal of application to taking care of our yards and gardens. For example, none of our practices recognize that Soil Foodweb scientists have now shown most flowering perennials and conifers, as well as most tree fruits, ornamental trees and shrubs do far better in soils dominated by fungi. Lawn grasses, vegetable row crops and flowering annuals, on the other hand, grow best in soils where the bacteria dominates. We need to take advantage of this new knowledge.

And there are lots of new scientific discoveries outside of the Soil Foodweb that impact home yard care and gardening, like the use of red plastic mulch to speed home garden tomato production.

New tools, new methods, new reasons. It is time we take gardening out of the dark ages (where some of our practices literally originated), and substitute Science for the Art.

I am not talking about a conversion to Organic Gardening. OG tends to be blindly religious in its application, often has less than scientifically supportable tenants and has always been slow in accepting change. No, this is Scientific Gardening, SG, and while it includes many of the same tenants as Organic Gardening, it is about knowing why, testing and improving the science of gardening.

I don’t have all the answers, but I am committed to work on them. We will need nurseries to carry new products and tools, but I am convinced they will. We will have to experiment and exchange ideas to come up with new methods applicable to Alaska.

There will be mistakes as we go, but it will be fun, interesting and safe. And, I know your plants will thank you.

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