Soil Improvement Tips for Healthy Garden Soil

Your soil improvement efforts will be more effective if you think of garden soil as a living web of microorganisms, not an input-output system.

| April/May 2009

Have you given due consideration to building your garden soil this season? What soil improvement techniques were you planning to use? Whether you’re filling new beds with bags of compost or tinkering with loam you’ve been nurturing for years, your first task may be to change the way you think. Sure, soil holds roots in place and helps them find moisture and nutrients. But truly superior soil goes beyond providing plants with a comfortable place to live and a seat at nature’s table. When it gets really good, soil does things we humans are just learning to appreciate.

Some gardeners think that building better soil is mostly a matter of adding the right amounts of the right organic amendments, and this is basically true. Above-average levels of organic matter are one key to developing soil that functions well as a nutrient storehouse and is a root-friendly place to be. But looking to compost or any other type of organic matter as the one thing your soil needs is like reading the first chapter of a book and saying you’re done. There is much more to the story.

Mulch More, Dig Less

Take microscopic fungi, for example. Some beneficial, soilborne fungi help some plants take up phosphorus, and others manufacture nitrogen — two of the big three plant nutrients normally provided in a bag of fertilizer. In return, the plants provide nutrients and a habitat for these helpful mycorrhizae, a general term for microcritters that live in, on, or alongside plant roots. We can’t see them, but they are down there, big time.

The group called arbuscular fungi is especially interesting, because many of them penetrate plant roots with a spider web of branched hyphae (fungus “roots”), which also spread out into the surrounding soil. This symbiotic union extends the plant’s root system, helping it gain access to nutrients and moisture that would otherwise be out of reach. In return, the fungi get a share of the carbohydrates produced by the plants. As hyphae die (the invisibly small structures live for only a few days), the decomposing tissues feed bacteria, protozoa, and all kinds of microscopic soil critters. And as this food web thrives, it releases nutrients for your crops.

The story gets better. The hyphae and spores of these plant-friendly fungi are coated with a sticky substance called glomalin, identified and named as recently as 1996 by USDA scientist Sara F. Wright. Glomalin is largely responsible for a soil’s tilth, or crumb structure, and it’s part of the soil’s nutrient storehouse, too. More soilborne fungi (producing more glomalin) lead to healthy, happy plants. Glomalin is also one of the compounds responsible for that earthy smell of fertile soils.

Each time you slather on some compost or mulch, you add starter colonies of these helpful fungi to your soil. After that, they basically want peace and quiet. Minimizing soil cultivation is the best way to host a robust mycorrhizal mob, because digging breaks up their hyphal networks. In the off-season, use of oats, rye and other grassy cover crops, on the other hand, turns your garden into mycorrhizal heaven. In nature, these beneficial fungi are always plentiful where deeply rooted grasses grow.

5/15/2015 2:06:32 PM

Thank You!

hazel Watson_2
5/9/2009 12:34:32 PM

I'm starting garden spots (mostly vegetable, some flowers and shrubs) where only grass has been grown for years. Using two methods: one, using paper, corrugated cardboard, or black plastic, I'm covering areas of the grass surrounding the new planting, with holes just large enough for the desired plants; the second is scooping all the grass away from the area, then scatter-planting seeds of annuals. Right now I'm hoping the first works better, because it's a lot easier! In both cases, I'm mulching the areas with last year's leaves and straw. I'm also building compost, some right in the gardens, and two large piles of cut weeds, grass, leaves and kitchen scraps. My intention is to spread it onto the gardens next spring.

Steve Thyng
5/8/2009 12:03:33 PM

The limited tilling concept is well explained here, but is based on the assumption that the laqnd in question is being used regularly as a garden. It recognized the fact that bacteria, etc in soil is disturbed by tilling, and therefore the processes ocurring in the soil which promote optimal plant growth are disturbed. There is more information on all this in a book entitled "Roots Demystified", by Robert Kourik, published by Metamorphic Press. The author explains that soil bacteria can be understood in terms of three fairly distinct layers: top, middle, and bottom. The top layer is only 3 to 4 inches deep, and the bottom layer starts about where subsoil begins and goes down. Each layer has bacteria, etc which is unique to it. When the soil is disturbed greatly, as I do when I til an area to 12+" deep and hoe the soil into a pile, place 2+' of leaves and brush in the area, cover it with about 5" of horse manure and then shovel the hoed out soil on top of it. Mr Kourik explains in his book that it will take awhile for the bacteria to find its place again after it has been disturbed, but that eventually it will settle in. I am expecting that my 'developed' areas will not produce well for awhile, but that they will eventually. I am "raising" areas like this to overcome a drainage problem, and am hoeing out the soil because I can't see the sense in burying good topsoil. Any comments, ideas on this method?

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