The Rural Voice, 2003-02, Page 34Gardening
What makes good potting soils?
Rhea
Hamilton -
Seeger and
her husband
live near
Auburn. She
is a skilled
cook and
gardener.
By Rhea Hamilton -Seeger
Choosing a potting soil mixture is
almost like choosing the best cake
recipe. Ask any gardener about what
they use to start their seedlings and
you will get such an assortment of
answers you will wonder how anyone
ever decides what to use.
Different plants require different
soil mediums depending on their
natural environments. You wouldn't
start a tropical house plant in a soil
meant for an alpine rock lover. There
is a wide selection of potting
mediums available, so why would
you mix your own? Probably for the
same reason you bake a cake from
scratch instead of buying a mix.
So what is available for mixing
and what can it do for my seedlings?
A potting soil mix is preferred over
straight soil because it is relatively
free from pests and diseases and is
light and well-aerated. Specifically
made seed soil mix is moisture -
retentive, fine textured, and low in
nutrients (because mineral salts can
harm seedlings.) If you use your
basic garden soil then it should be
screened to remove sticks, coarse
stones etc.
There are some packaged soil
mixes on the market. Some are
labelled as sterile
but growers
30 THE RURAL VOICE
often recommend that you should
sterilize it again. I have heard about
sterilizing soil in your oven to reduce
or eliminate fungus and harmful
bacteria — I just couldn't bear to put
soil onto one of my cooking sheets. I
am glad I hesitated. Apparently, the
whole process can leave your kitchen
reeking and will haunt you long after
the seedlings are out in the garden.
Another suggestion is to sterilize
your soil by heating it on a cookie
sheet on a backyard barbecue to 180
degrees for 30 minutes (use a meat
thermometer). The purpose is to burn
off harmful fungi and bacteria that
cause dampening off. Some
gardeners advocate that there are
some beneficial organisms and
bacteria in the soil and sterilizing is
more detrimental than beneficial.
You could treat the soil with a mild
fungicide before starting your seeds.
On the plus side, soil is heavy,
which can help anchor wobbly
seedlings. Soil based mixtures
contain trace minerals which help
nourish your plants and reduce the
need for excessive fertilizer.
Soilless mixtures are lighter,
cleaner, less expensive and easier to
use than soil. On the flip side, they do
not provide the minerals required so
therefore new seedlings will need
more frequent fertilizing. If allowed
to dry out, you can have a real
problem trying to get the soilless
mixture moistened again.
A soilless mixture may contain
any of the following ingredients. Peat
moss is the compacted, partially
decomposed remains of reeds,
mosses, and grasses. It improves a
soil's ability to retain moisture and
air but it does not add any nutrient
value and once it dries out you will
have a "dickens" of a time getting it
moistened again. I have developed
an almost political stance on peat
moss. It is classed as a non-renewable
resource and companies are tearing
up bogs around the world to feed the
rapidly growing demand for peat
moss. There are alternatives for our
potting mixtures that we have to seek
out. There, that is my condensed
diatribe for today. Please seek out
peat substitutes.
Pumice is a crushed form of
volcanic rock. It is the same as the
pumice stone that you would use on
your feet. It will absorb five times its
weight in water and, like perlite, adds
aeration and drainage and lightens the
weight of the mixture.
Perlite is a light, white, round
aggregate derived from volcanic
glass. It absorbs very little water but
does hold some in its surface nooks
and crannies. It acts like a coarse
sand. It helps provide aeration,
increase drainage and lighten the
weight of the potting mix. Look for
the horticultural grade (size). It is so
light it will float to the surface when
a pot is watered.
Vermiculite is that shiny, metallic -
brown material that is made by
heating particles of mica in a furnace
at more than 1,000 degrees. Like
perlite, vermiculite provides the air
spaces necessary in a growing
medium. Unlike perlite, vermiculite
absorbs as much as 16 times its
own weight in water. It is also
chemically active, binding and
releasing minerals. But vermiculite
will compress with time and have to
be replaced. There is one thing that
disturbs me and that is the amount of
energy that it must take to produce
this material. We are an energy .
hungry society and while trying to
"get back to nature" we are still
sucking up energy in gross amounts
to produce products that we could do
without if we ever gave it a little
consideration. I only hope this
material is a by-product
of something else.
A basic, all purpose potting
mixture is one third sand, one third
compost and one third clean top soil
topped off with a light treatment of
fungicide. Use a coarse sand, not the
fine aquarium sand that will clog
up your soil. You can add bonemeal
as a slow release fertilizer.
Cleanliness counts and making
sure that your pots, containers, and
tools are clean will help cut down any
problems you may have when
starting your seeds. Happy
gardening.0