Think Like a Microbe, Act Like a Root
by Rommy Lopat

ARTICLE FIRST APPEARED: 1998 Summer

TWG Editor: I hear more weird information about soils passed around than about any other topic. The last time was when my friend said her husband's favorite activity was rototilling and then rototilling some more--even in the rain. Egad! A soil sadist! Here's a reprint of an earlier article on improving soils:

Honor What Mother Nature Bestowed: Whatever kind of soil you have--sand, silt, or clay--it has a particular structure. You may have several soils on your property, each one suited to particular plants and their roots. Gardens, gardens, and more gardens!

Do No Harm! The second you put a shovel into the ground, you are changing the structure of the soil. Do no harm! A gardener with a shovel is the same as a farmer with a plow. We want to move the soil, throw it around, bring in new kinds, add salty composts, walk on it, and plant plants with short or slow-to-decay root systems. Unlike Mother Nature, we are tidy: if a plant dies, we are quick to remove it rather than letting it stay to feed our microbial pals. Agh--easy to make the soil wetter, drier, harder, chemically unbalanced.

The Gardener's Goal is to develop a deep "prairie-like" soil (unless, of course, you are creating an alpine garden or whatever). In a prairie, organic material is distributed all the way down to the subsoils. Prairie grass has deep, deep roots: indeed, most of the prairie's organic matter is concentrated below ground. These fibrous roots spread, penetrate, and die quickly (3-5 years; a tree's roots, conversely, take "forever" to decompose, so note that forest soils are not deep) and then get eaten by microbes which die, fat and happy, decompose, and become humus. The humus--accumulating year after year--is what creates tilth: soil structure with lots of space for air and water vapor. A few tips on achieving a "prairie" soil:

• Be patient. Build the soil first even if it means your garden waits another year before being planted.

• Work a soil only when it's moist; any other time (too dry; too wet) and you are ruining its structure by compacting it or pulverizing it. If the landscaper wants to work in the rain or drought, send her home--she's a soil sadist.

• Don't overtill. 1 or 2 passes with the rototiller is plenty. Lumps are better than pulverising the soil structure. Better to let earthworms act as your rototiller.

• Tell your sub-division's developer that you won't buy the house if he removes the topsoil. If it's too late and you've already built the house, don't get mad at the landscape contractor when she says she wants to import LOTS of "garden soil mix". If you want a garden, you must provide deep soil.

• To create a garden in heavy clay, double-dig 50-60% (!) aged compost by volume into the soil or create a raised bed. Even in a raised bed, mix the old top layer with the new bottom layer before procceding to fill the bed completely. Simply layering new soil on top of old soil won't improve aeration if the soil underneath is hard.

• Dig in 1-3" of compost every year. More is not better: if you layer more than 3" on top without incorporating it, you are creating a new soil layer that is very porous and which microbes will not enter. Also, roots planted in the new layer will not go any deeper, thus defeating your goal.

• Use aged compost (over 4 months) or risk salt damage. If you must use fresh, use 50% shredded leaves and 50% new grass clippings, or fresh wood chips with nitrogen fertilzer mixed in; or alfalfa-eating-horse manure mixed with sawdust.

• Perform a soil test every four years.

• Core aerate your lawn every year.

• Sandy soils can use some clay. To lighten clay, don't add sand or gypsum unless you know the BIG drawbacks.

• High-fired calcine clay products such as 'Profile Professional Clay Soil Conditioner' are an effective way of preventing compaction while holding water and nutrients until needed. Rock gardeners (always concerned about drainage) practically eat Profile [Turface=wholesale name) for breakfast, as do football stadium groundskeepers. Great indestructible stuff, but it costs real money. Homemade compost is far cheaper.

• Grow prairie plants with long root systems as your "clay busters" [Prairie Nursery term]. Use New England Asters, Coneflowers, Stiff Goldenrod, Ironweed, Smooth Penstemon [P. digitalis],

(TOP OF PAGE)