Re: Bed Preperation
Patty Forster wrote:
> I need some advice on the preperation of a new bed for irises. My soil here
> in Raleigh, NC, is solid clay with boulders that I have to remove. We have
> a horse barn in the neighborhood. Should I add manure in when I till the
> bed? I will be adding well established manure, not fresh and also pinebark
> mulch for drainage.
Patty,
When I built my raised beds (because I have clay and gophers) I filled them with
a mixture of 25% topsoil, 25% sand and 50% redwood soil conditioner (shredded
redwood - we have a lot of that here) The idea was to have lots of slowly
decomposing organic matter. In your case you would want to use local materials.
I have used horse manure in other gardens and if it is well composted and a lot
of the straw/ hay/ oat seeds are dead it seemed to work well. Sometimes the feed
seeds are just a problem for a while.
Below is an article I scanned in by one of the staff at UC Berkeley on clay
soils. I hope you find it useful.
Lightening Up That Heavy Soil
Clay can be turned into decent dirt
Clay soil is the curse of many Bay Area gardens. It's sticky and mushy when
wet; hard as cement when dry. In fact, dried clay soil is so hard that people in
underdeveloped countries have: traditionally used it to make bricks for houses.
Of all soil types, clay soil is made up of the finest microscopic particles,
says Bob Raabe, professor emeritus of plant pathology at the University of
California at Berkeley. "As a result, there is very little air space between the
soil particles."
And this causes problems.
"Lack of air causes clay soil to hold moisture," says Ann King, environmental
horticulture adviser at the UC Cooperative Extension for San Francisco and San
Mateo counties. "Moist conditions and limited air at the root zone lead to root
disease." And low oxygen at the root zone also means that plants have difficulty
absorbing nutrients.
To determine whether you have clay soil, try the "sausage test," says Lou
Truesdell, president of American Soil Products Inc. in Berkeley, a company that
recycles urban green waste into compost and other horticultural products.
Roll some damp soil in your fingers to make a sausage a quarter of an inch wide
and about an inch long. Then hold the sausage at one end. If it doesn't break,
you probably have clay soil, says Truesdell. If it crumbles, you have a loamy
soil, and if you can't even form a sausage, it's sandy.
Not All Bad
Despite its drawbacks, clay‹which makes up most of the Bay Area's soil and a
good deal of California¹s does have some benefits.
³I happen to have sandy soil in my yard, and I'd much rather have clay soil,"
says Raabe. "Sandy soil doesn't retain water and nutrients like clay soil. Clay
soil needs to be watered and fertilized much less than sandy soil."
Clay soil is also bulky and helps keep large plants anchored and stable.
Best of all, if clay soil is amended on a regular basis with organic materials,
it can become a rich, easy-to-work soil that will encourage plants to thrive,
says Raabe.
"We've been amending a garden plot of clay soil at the university for the last
20 years, and its structure has really changed," he says. "Now the soil is
aerated, drains well and can be easily worked. Sandy soil doesn't change as much
when amended."
Amending with organic matter, says King, "adds air space to the soil and
promotes better drainage. It also relieves the stretching and shrinking that
occurs with clay when the ground becomes wet and dries out."
Good soil amendments include homemade or bagged compost (the favorite of most
experts), composted manure, planter mix, peat moss (in combination with other
organic matter), leaf mold, bagged shredded bark and ground up garden waste.
Some experts suggest composting ground-up garden waste until it breaks down
before amending soil with it, but Truesdell says it's often not necessary to
wait long.
"I think it's good to amend with materials that will continue to break down,
because then you get better biological activity in the soil," he says.
"Some people warn against this, because it can cause a loss of nitrogen. But I
don¹t think it¹s usually a problem. If your plants have a high nitrogen
requirement, simply add a slow-release nitrogen fertilizer or composted animal
manure to compensate."
Other experts suggest adding gypsum to clay soil to improve drainage, leach salt
from the ground and add calcium to the soil. The higher the calcium level, the
more acidic the soil. And acidic soil is better for most plants.
You wouldn't want your soil too acidic, however, warns Truesdell, or plant
growth will suffer. To determine your soil's pH and to know what amendments to
use, Truesdell advises getting a soil test. You can get your soil analyzed at a
soil agricultural lab for about . $25.
Although it seems like a logical amendment, never mix sand into clay soil, says
King. "Concrete is made of clay and sand, and concrete is what you'll get if you
mix these two," she says.
Instead, regularly amend with a lot of organic matter. One small application
won't do much. If you have a heavy clay soil, it will take years of continuous
amending to get the soil in good shape, as bacteria convert the amendment into
much smaller amounts of humus.
Digging It In
"Add as much organic matter as you can," says Truesdell, who suggests adding
one-third to one-half amendment to the top six inches of soil. Do this by
spreading two to three inches of amendment on top of the ground, then mixing it
in thoroughly with a spade or rotary tiller.
"Although this may seem like a lot, after a year, one-third to one-half of what
you added will be gone," he says. Gardeners with particularly heavy soil may
have to amend it three or four times a year to keep it in good condition.
In warm weather, the surface of clay soil hardens and cracks, which impedes the
infiltration of water and air into the soil. To combat this, experts suggest
mulching ‹spreading organic material on top of the soil. Mulching will allow
better water penetration and slow down water evaporation from the soil into the
atmosphere. Mulch also slowly breaks down and adds nutrients to the soil.
Never amend or plant in wet clay soil, as working it then will badly damage the
soil structure. When the soil dries, you'll end up with hard clods of earth that
are nearly impossible to break up.
To determine whether clay soil s ready to be worked, Raabe suggests sticking a
spade into the ground and pulling it to one side. If the soil looks glossy and
slippery, it's too wet to work. If it has a dull surface, go ahead and dig.
Waiting Period
How long you'll have to wait after rain can range from several days to a week or
more, depending on how much clay the soil has and how warm the weather is.
Be careful not to overwater clay soil; it needs less than other types. Don't
automatically irrigate when the surface is dry, because underneath it might be
very moist. Make sure the top inch or two is dry before watering.
--
John | "There be dragons here"
| Annotation used by ancient cartographers
| to indicate the edge of the known world.
Fax: | (510) 795-9723
John Jones, 35572 Linda Dr., Fremont CA, 94536
jijones@ix.netcom.com, USDA zone 8 (coastal, bay)
