Soils
TWG Editor: Parts of the following are paraphrased, with permission,
from the book entitled,Where the Sky Began [IA State University Press, 1995] by the late
author, John Madson. Please read his chapter, “Prairyerths”, for yourself. Then
devour the rest of the book, which is available by calling (515) 292-0140.
The best way to figure out how to create a good garden soil is to imagine
your property as it was 200 years ago before a white man came along. Imagine that on your
property was a prairie or a forest or a floodplain. Imagine that those lands received
adequate sunshine and the effects of a temperate climate (still pretty much the same
today) in which the rate of plant decomposition is relatively slow and steady, unlike
Canada (where organic matter is too cool to decay quickly) or Florida (where it’s so
hot that organic matter will decay even before humus can be formed). There was balance.
If your land was part of the grassy prairie, your property once had the
best soils on earth. Virgin prairie soils are several feet deep, with high levels of
nutrients and a wealth of organic material distributed all the way down to the subsoils. A
permanent sod of prairie grasses has deep, deep roots, and so most of the prairie’s
organic matter was concentrated below ground. This structure allowed the plant to survive
fire and have enough energy to spring up afterwards. A prairie grass’s long, fibrous
roots spread, penetrate, and die quickly (maybe in 3-5 years), and then get eaten by
microbes (bacteria, fungi, ants, earthworms, etc.), which die fat and happy, decompose,
and become humus. The humus—accumulating decade after decade—is what creates the
fine structure of soil: soil with lots and lots of space for air and water vapor. Soil
that bounces like a sponge. Soils which have tilth.
Contrast the prairie with the forest, where little humus is created
because the organic matter of trees is concentrated above ground, in their leaves rather
than their roots. Tree roots decay (compost) very slowly, so your most fertile soils are
right at the surface where the leaves fall. Forests lack those deep roots creating deep
soils, although they may have good tilth if there are earthworms around. Even so, forest
soils probably won’t have the mineral content of lands enriched by grasses. Grasses
simply return more calcium, potassium, and other bases to the soil than trees do.
Lastly, the floodplain soils, or “bottomlands”. Here is where
soft-wooded trees grow rather than grasses and forbs, so leaves are the only regular
source of humus. But they are washed away frequently before they decompose, and the water
creates heavy, poorly-aerated soils. Even earthworms can’t survive, so the soil
becomes very heavy although fairly rich in organic matter.
Now, understand that most of us gardeners are exploiting the land just as
sure as if we were farmers with big plows. We want to dig up the soil, move it around,
bring in new soil, throw on tons of acidic, salty commercial compost which hasn’t yet
become stable humus, and plant turf, violets, and trees. What do most of these ornamentals
have in common? NO GREAT BIG ROOT SYSTEMS! No roots to hold the soil and its minerals in
place, no roots to turn the soil naturally, no roots to decay and create humus, no roots
to feed the microbes that convert nitrogen in the soil into food for the plant. The
bacteria have gone dormant, waiting for a long fibrous root to arrive with a good meal.
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TWG Editor:My thanks to Kevin Zanzinger of the Chicago Botanic Garden,
Jim Fizzell of Jim Fizzell & Associates, and Ellen Phillips of the DeKalb Coop. Ext.
Service for reviewing these ideas on soils. The opinions herein are TWG’s.
HOW TO HAVE GREAT SOIL!
1) Honor what Mother Nature gave you as your soil. Whatever kind of soil
you have—sand, silt, or clay—it has a particular structure. You may have several
soils on your property, and you must consider each one as a different “garden
type” suited to particular plant types or root types. As soon as you put a shovel in
the ground, you will be changing the structure of the soil. Beware!
The goal of the gardener is to develop soil that not only has lots of
organic material, but also has an active microlife that constantly eats the organic
matter. The microbes determine the amount of nutrition available each day to the
plant’s roots. When clay soil becomes compacted, there are fewer large pore spaces.
While air is still exchanging and water is still present, they have ‘slow going’
through the soil. The microbes don’t eat, the organic matter doesn’t decompose,
and the humus (which creates the soil structures that in turn create the tilth that guards
against compaction) is not formed. Compaction is easy to do: nature’s everyday wear
and tear on a soil can reduce plant growth by 10 percent (USDA report). No amount of
fertilizer or additions of mycorrhizal fungae can compensate for lack of air: you’re
suffocating the roots and the microbes!
A few more suggestions:
2) Work a clay soil only when it’s moist; any other time (too wet;
too dry) and you are back to ruining its structure by compacting it or pulverizing it.
Don’t demand that your landscaper work in the rain or extreme drought; indeed, insist
that she go home unless she never leaves the stepping-stones.
3) To create a garden in heavy clay, you can double-dig 50-60% aged
compost by volume into the soil or create a raised bed of same. Dig the aged compost in as
deep as possible: adding aged compost to the surface won’t improve the soil’s
aeration if the soil underneath is hard.
4 Add aged compost every year. Best to dig it in but mulching with it in
amounts of 1-3” will be ok. If you add more, make sure you dig it in deeply. Simply
putting a thick layer on top of the soil every year is extreme: you are creating a new
soil layer that is very porous, and the microbes will not travel up into it. Also, roots
planted in such a delicious mix will never leave it to go deeper. But without aged compost
added every year, the soil will revert to its old self.
5) Make sure the compost you use has been aged for about 4 months and is
no longer hot or you risk salt damage. If you’re using fresh organics, try 50/50
shredded leaves and grass for perfect balance. If using fresh wood chips, sprinkle some
nitrogen underneath first.
6) Have soil tests performed every 4 years so that you understand the
nutritional level of your soils.
7) Plants with great big root systems are the best “clay
busters”, a term coined by Neil Diboll of Prairie Nursery. Black-eyed Susans,
Liatris, New England Asters, Joe Pye Weed, Big Bluestem, Little Bluestem, Purple
Coneflowers, Beebalm, White False Indigo, Canada Wild Rye, Indiangrass, Switchgrass,
Culver’s Root, and Ox-Eye Sunflower do fine in clay and help mix it. They are Mother
Nature’s answer to clay soils. But don’t expect even the prairie plants to do
the impossible: you must help open up any concrete-like clay first.
8) Builder’s sand added to clay will change its texture and help
maintain its large pore spaces, but only in very large amounts. [Consult the UofI
publication, “Amending Soils with Sand”, (217) 333-2007, before trying this
yourself.]
9) Incorporate high-fired clay products like ‘Profile Professional
Clay Soil Conditioner’. An anti-compactant that also holds water and nutrients until
needed, Profile is being used in the new TWG garden.
10) Core aerate your lawn every year.
11) Create a earthworm “catcher” (a large rock with moist soil
underneath). somewhere in the yard. Go harvest the earthworms on a regular basis, and put
them in your garden. They are Mother Nature’s rototillers. I’m told that the
earthworms you buy through the mail are a waste of money. Native worms, not
“exotics”!
12) Don’t overtill. 1 or 2 passes with a rototiller in the garden is
plenty. Better to have a few lumps than to pulverize the structures in the soil. Balance!
Balance!
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SOIL TEST LABS
There are many labs located in the region. These are just four. Contact
your county's Coop. Extension Service.
A&L Great Lakes Lab 3505 Conestoga Drive Ft. Wayne, IL 46808-4413
(219) 483-4759 ‘Beyond the basics’ tests at various prices.
Green Gems PO Box 6007 Healdsburg, CA 95448-6007 (800) 431-SOIL This is a
mail-based testing kit which is also sold in garden centers. The actual lab work is
performed by A&L Great Lakes (see above).
Woods End Research Lab PO Box 297, Old Rome Rd. Mount Vernon, ME 04352
(207) 293-2457 In April, Woods End will debut a home-test kit for soils similar to one
they have for measuring the maturity of compost piles.
Ag Source Coop Services (aka The Soil Doctor) 106 N. Cecil St. Bonduel, WI
54107 (715) 758-2178 The tried & true basic test. This is the one the IL Cooperative
Extension Service will probably refer you to, but it's quite elemental.