To: "homestead AT lists.ibiblio.org" <homestead AT lists.ibiblio.org>
Subject: [Homestead] Garden soil: it's much more than dirt
Date: Thu, 03 Mar 2005 08:02:53 -0700
The Push Is on for Good Clean Dirt
By ANNE RAVER
Published: March 3, 2005
I'd been an organic gardener for years before I really looked at pictures
of soil under a high-powered microscope.
Mites were feeding on springtails. Fungi were swirling like strands of
spaghetti around plant roots. Nematodes shaped like torpedoes were grazing
on fungi. Everything was eating everything else.
Fascinated, I began talking to soil scientists and compost experts,
learning that plants are not just taking up nutrients. They are exuding
carbohydrates through their roots, feeding the bacteria and fungi that in
turn break down nitrogen, protein, phosphorus and many other elements into
forms the plant can absorb. For the first time, I began to grasp what I was
dealing with in the soil of my garden: an underground city more complex
than the infrastructure that powers Manhattan.
For the last 30 years, even as organic gardening grew from a fringe
movement to a mainstream pastime, the science of soil has remained the
province of microbiologists and plant pathologists, along with a few
gardening geeks. But now there is an increasing awareness, even among
casual gardeners, that soil has a huge effect on the success, or failure,
of their gardens, and those gardeners are spending more money every year on
soil-enriching products. Between 1999 and 2003, according to the National
Gardening Association, the number of American households buying organic
fertilizer nearly tripled, to 11.7 million.
And as everyday gardeners face a growing profusion of such products - from
Peruvian seabird guano to compost tea brewing machines, from micorrhizal
fungi to beneficial nematodes - they are trying to figure out which ones
are valuable, which are little better than snake oil, and whether their
gardens need any of them. For those who have found the right mix, the
rewards can be considerable. "I had some pretty sad geraniums, but now the
whole greenhouse is full of color," said Carol Magadini, a garden designer
in Mendham, N.J., who has started using a compost tea on the plants. And
after she started using a natural fertilizer on her moonflowers, which were
"iffy," she said, "they had 50 blooms a night."
For gardeners who want to start taking soil seriously, the best way to
begin is by taking samples and having them tested.
State universities usually offer testing services or will direct you to a
reputable private laboratory. Ask for a textural analysis, which will
indicate the percentage of clay, silt and sand in your soil, and how well
it drains. And ask for a complete nutrient analysis as well, which will
give you ammonium levels, elements and micronutrients. Such tests can range
in cost from $15 to $75.
[I use a simple way to see the textural mix of my soil. I fill a quart jar
about one-third full with dirt, add water nearly to the top, screw on a
tight lid, shake vigorously for a minute or so until all soil is dissolved,
and place the jar on the window sill in front of my kitchen sink. The next
day the mix is obvious. The clay is on the bottom, the sand is next, then
the loam, and the light humus is at the top. Serious gardeners also may
want to buy their own soil test kits. --Gene]
Eric T. Fleisher, the director of horticulture at the Battery Park City
Parks Conservancy, also recommends a simple percolation test. Dig a hole
about a foot deep and half as wide, and scarify the sides with a garden
fork or hand cultivator. Put two inches of sand or gravel in the bottom,
fill it with water and note how quickly it drains. It should drain at least
an inch an hour.
Most gardening problems have to do with poor drainage, said Mr. Fleisher,
who manages 36 acres of organic gardens.
"Simply adding compost to heavy clay won't help, if you're not improving
drainage," he said. So, depending on the density of your soil, you may have
to dig down, with a pick ax and spade, 18 to 24 inches, just to break up
that compacted clay. Then use a garden fork to mix in coarse washed sand,
compost, aged leaves and aged manure.
Once you have workable soil, use that spade as little as possible. And put
the tiller away. Every time you churn your soil into fine-grained cocoa,
you are slicing through earthworms and killing beneficial organisms,
toppling the delicate city that these organisms are building underground.
Professional analysis can also reveal problems with nutrients in soil,
nutrients that, even if they are present, may be unavailable to plants for
any number of reasons, from a lack of oxygen to an excess of nitrogen.
Excess calcium, for instance, can inhibit the uptake of magnesium, boron
and potassium, elements all crucial to plant growth.
"People often see browning on leaves and think it's a nutrient deficiency,
when actually it's an excess of calcium or magnesium," said Dr. Olaf
Ribeiro, a plant pathologist who runs the Ribeiro Plant Lab on Bainbridge
Island in Washington.
Dr. Ribeiro has rallied failing 200-year-old Douglas fir trees in Olympia,
Wash., he said, by applying compost full of micorrhizae, or beneficial
fungi, which colonize tree roots, transporting nutrients and protecting the
tree from disease. He has solved problems in citrus groves and vineyards by
applying compost tailored to the needs of the soil and the particular
plants being grown. And he sprays his own roses with sea kelp, which
inhibits powdery mildew, he says, and makes the plants vigorous, the leaves
a dark green.
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But gardeners who are unaware of the chemistry of their soil can often make
problems worse, Dr. Ribeiro said, for example by pouring on fast-acting
synthetic fertilizers. The extra nitrogen in such treatments may green up
plants, but, he said, it also "helps pathogens to increase rapidly."
And poorly made composts or mulch full of pathogens can also cause serious
damage, if not more, said Dr. William F. Brinton, the president of Woods
End Research Laboratory in Mount Vernon, Me. "I would not buy any product
sight unseen before knowing where it came from and what's in it," he said.
"There is a lot of E.coli in compost that is improperly made."
Dr. Brinton, who has a doctorate in environmental science, is certainly not
opposed to compost. He founded Woods End in 1975 to help companies make
compost out of yard waste, crab shells, chicken manure and a myriad of
other waste products.
"I thought compost would save the planet," Dr. Brinton said. "But compost
is turning into a sleazy big business. There is a powerful waste lobby
making money processing waste into compost," he said, without regard to
what pathogens might be carried in the material.
Dr. Ribeiro also pointed to problems with mulch, or composted yard waste.
"Up here we get a lot of wood chips, which worries me, because they could
be from diseased trees," Dr. Ribeiro said. Phytopthera, which can attack
1,000 species of plants, from potatoes to oak trees, is often spread
through contaminated mulch.
So if you are buying mulch, get a printout from the company or municipal
group providing it, listing everything in the material. "That means
microelements to major elements," Dr. Ribeiro said. "You can have too much
nitrogen in compost, or high levels of micro-elements like lead and cadmium."
And what about all the claims of miracle cures with compost tea? The
ancients, from the Romans to my grandmother, just steeped manure in a
bucket of water. But over the last few years fancy brewing machines that
aerate compost mixed with water have become the new Cuisinarts of the
garden. The resulting teas are supposed to cure everything from powdery
mildew to potato blight. There are testimonials from potato and citrus
growers, golf course superintendents and public garden directors. But so
far these testimonials haven't been backed up by scientific studies.
Scientists warn that the teas can be infected with pathogens if they are
improperly made.
Dr. Brinton was one of 13 scientists on the Compost Tea Task Force
organized by the Department of Agriculture's National Organic Standards
Board, which completed a study of the efficacy of compost teas in 2004.
"We came to the conclusion that with the uncertainty of compost quality out
there, there's considerable risk," he said.
The best way to know what you're getting, of course, is to make your own
compost, and local botanical gardens can teach you how to do it. Cities and
counties often give away composted yard waste. And don't bag up those
leaves for the trash collector. Let them decay right under your tree, to
feed the soil. Or put them on your compost pile.
[Shred leaves with your mower before putting them on the compost pile.
Unshredded leaves make a thick, slimy impervious layer and take forever
to break down. --Gene]
I've been making my own compost for 30 years. I've raised red worms and
spread their castings on my house plants. I've mulched my garden with
seaweed gathered along the bay. But I've only just begun to discover the
secrets of the soil.