Re: CULT: sand as soil amendment



amyr@jump.net wrote:
> 
> > Message: 20
> >    Date: Sat, 30 Dec 2000 11:01:04 -0800
> >    From: "Loberg" <loberg@jps.net>
> > Subject: CULT: Adding sand as soil amendment
> >
> >     Although I've heard several threads talking about amendments, pros and
> > cons... most recently about the Humor in OK, one thing I've not heard much
> > talk about... does anyone add sand or equivalent in large quantities to
> > their iris garden beds?   Not just a covering, but till it in?   I don't
> > need to because my soil already drains well, but as I think about those who
> > say they have clay or heavy clay, I'm just wondering if adding huge amounts
> > of sand (or course builders sand as Rosalie once said) would help.    Not as
> > a substitute for other nutrients, but to lighten the soil and make it drain
> > better.    Anyone with reports on using sand?
> > Kitty Loberg
> > northern Calif.
> 
> You can only use sand *if* you also add plenty of organic matter,
> as the fellow who replied to you used peat moss, else you will
> end up with concrete bricks!  :-)  Once you have done this, you need
> to keep adding as top dressing or tilling in more organic material
> as the original stuff breaks down and decomposes, unlike the clay
> and sand.


This is an excellent example of how we must be cognizant of the fact
that no two areas or environments are the same and what works well in
one area may not in another and that experienced iris growers local to
one's area are one's best source for information.

It is also the reason we ask everyone to include their USDA Zone or some
other description of their environment so others have a better idea of
how to intrepret your comments. Most mail programs (except notably AOL)
allow you to specify a signature file that can be added automatically to
the end of each message.

Concerning clay:

In the archives, Louise Parsons wrote:
_______
For clay soils:

"it is a good idea for all to seek local advice from your Extension
Agent, Soil Conservation Service and/or a local club concerning soil
prep. There are reasonable ways to deal with clay soils, but clay
chemistry is highly variable. For example, gypsum works well in some
clays, but is a total waste of time in others. In some clay soils, fine
builder's sand is a good amendment, in other types of clay, you will
unwittingly create concrete! This is why local advice is important.  You
have lots of garden clubs and wonderful sources of info in the Raleigh
area, so don't break your back or give up on your soil.  Clay has some
good aspects to it.  In general Bearded Iris like a lean mineral-rich
soil and too much fluffy organic material will promote rot."

I had an article from the University Of California at Berkeley that I
scanned in:

"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, clayÐwhich 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 Ðspreading 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.
________________________________________________

USDA zone 8/9 (coastal, bay) 
Fremont, California, USA 
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Director, Region 14 of the AIS
Director, American Iris Society
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