I thought I knew a lot about garden soil until I moved to
my present home and tried to plant my first garden there. I
wandered out with a shovel to turn the soil for spring
planting, and ended up scurrying for a pick-ax to break up
the hard-packed clay. It was a far cry from my previous
garden, which had such beautiful loamy soil that I could
(and often did) harvest potatoes simply by rooting for them
with my hands.
Obviously, I needed to know more about the relationship
between clay and loam before I could turn the former into
The first thing I learned is that clay is one of three
basic soil types, the other two being sand and silt. All
three are made up of rock particles. Clay, as I learned the
hard way, consists of fine particles that turn brick hard
when dry and that cling to a shovel when wet. Sand, I knew
from my years living in the Arizona desert, is coarse,
gritty, and porous, whether dry or wet. Silt lies halfway
between clay and sand. When wet, it sticks together but
doesn’t stick to a shovel.
Loam (aha!) contains a mixture of clay, sand, silt, and
humus. Since clay, sand, and silt are made up of rock
minerals, they comprise the inorganic component of loam.
Humus, by contrast, is decomposed plant matter and is
therefore the organic component. Good garden loam contains
at least S% humus, and humus improves sandy soil by
increasing its ability to absorb and retain moisture. It
also improves clay soil by loosening it, making the soil
easier to work, and preventing surface crusting so that
sprouting plants don’t have to struggle so hard to pop
through. This is just what my clay soil needed.
An obvious source of humus is used barn bedding, worked
directly into the soil. But it was spring and I was ready
to plant. I didn’t have time to wait for “hot” manure to
decompose. Fall is the time to work manure-soaked bedding
into the soil, in anticipation of spring planting. Another
obvious source of humus is compost, but I had just moved
and didn’t yet have a compost pile. I remedied that right
away by nailing some planks into a series of
four-foot-square corrals and tossing in all the kitchen
scraps, grass clippings, and other organic matter I could
get my hands on. Kept slightly moist and aerated by
occasional turning, the “pile” would one day provide all
the compost my garden needed.
Like any other source of humus, compost improves soil
texture and makes the soil easier to work. Compost also
adds nutrients and encourages the growth of beneficial
soil-borne microorganisms that dissolve those nutrients, so
they can be readily absorbed by plant roots. But my compost
pile was growing slowly and decomposing even more slowly. I
needed lots of humus in a hurry. So I called a local saw
mill and had them deliver several truckloads of well rotted
sawdust to till into my garden. Voila! I had loam. But it
wasn’t yet fertile loam.
Clay, sand, silt, and humus all contribute certain
nutrients that plants need in order to grow and thrive.
Just what kind of nutrients loam contains, and how much of
each, depends on three things: the sources of the mineral
and organic matter making up the soil, the degree to which
the soil has been weathered and eroded, and the amount of
nutrients used up by plants previously grown in the soil.
The major plant nutrients nitrogen (N), phosphorus (P), and
potassium or “potash” (K)-are the most likely nutrients to
be deficient in garden soil. Bagged fertilizers have three
numbers on the label (5-10-5, for example), representing
the percentage of each nutrient that the fertilizer
contains. Chemical fertilizers contain only those elements.
Fertilizers derived from natural sources contain, in
addition, a variety of micro nutrients, or trace elements,
that plants use in lesser amounts. While chemical
fertilizers can be manufactured to precise specifications,
natural fertilizers vary somewhat in NPK values, depending
on the source. Any good garden book lists various sources
and their average NPK values. If you buy a bagged natural
fertilizer, such as bone meal or blood meal, the label will
tell you the NPK value for that particular lot. Compared to
natural fertilizers, chemical fertilizers appear to be less
expensive. They also dissolve more readily in water, giving
plants a quicker boost. But because they dissolve so
readily, chemical fertilizers also quickly leach out of the
soil. Natural fertilizers, on the other hand, release
nutrients over a longer period of time. In the long run,
therefore, natural fertilizers are a better buy.
Natural fertilizers are a good deal for other reasons as
well. Compared to chemical fertilizers, they don’t burn the
delicate roots of seedlings, they don’t destroy beneficial
microorganisms in the soil, and they increase a plant’s
resistance to disease. Chemical fertilizers do just the
opposite, which works out nicely for the manufacturers of
chemical products, since they sell more insecticides,
fungicides, and other chemical poisons.
When you add lots of compost to keep up the humus level of
your garden, you don’t have to worry much about NPK. Good
compost provides most of the nutrients plants need. But if
you’re in the process of building up soil fertility, like I
am, your garden plants need an occasional NPK boost.
Furthermore, applying a little fertilizer at strategic
times helps any plant reach its fullest potential.
Strategic times to fertilize are: when a plant develops
true leaves, when it begins to bloom, and again when it
starts setting fruit.
If you have access to manure, you can provide a quick
nitrogen pick-me-up for any plant that’s about to bloom by
giving it a shot of manure tea. Cover manure in water and
let it steep for about a month, strain out the solids (toss
them into your compost heap), and dilute the liquid to the
color of weak tea.
Another good source of nitrogen is dried blood meal, a
slaughter-house byproduct. A good source of phosphorus is
bone meal, a slaughter-house product made of steamed,
ground-up bones. Heating it with wood gives you a ready
source of potassium in the ashes from your stove-about 50
pounds of ashes for every cord you burn. In addition to
supplying potassium, wood ashes also sweeten acidic soil.
Soil acidity (pH) is measured on a scale of 0 to 14; 7 is
neutral. Soil that’s be low 7 is acidic; soil that’s above
7 is alkaline. Extremes in pH tie up nutrients, and most
vegetables do best in neutral soil.
The ashes of dense hardwoods like oak and hickory are best
for sweetening soil. Apply no more than 20 pounds per 1,000
square feet per year. If your soil is on the alkaline side,
you can lower the pH by working in sawdust, leaf mold, or
peat moss. Because I used lots of sawdust to improve my
soil’s humus level, I also added ashes to balance its pH.
Now that I’ve got plenty of compost, my soil’s acidity
takes care of itself, since compost tends to neutralize pH.
Despite all the sawdust, ashes, and compost I’ve added, my
garden’s soil still isn’t perfect-but it is well on its
To find out what’s in the soil in your garden, fill a quart
jar one-third full with soil and two-thirds full with
water. Shake the jar and set it aside until the soil
settles into layers: The bottom layer will be sand; above
the sand will be a layer of silt; then comes a layer of
day; and on top of the water will float undecomposed
organic matter. A good mix contains about 20 percent clay,
40 percent silt, and 20 percent sand plus organic matter.
Another way to find out what kind of soil you have is to
squeeze a moist sample in your hand. If the soil forms a
tight, sticky ball, it contains too much clay. If it feels
grainy and crumbles no matter how hard you squeeze, it has
too much sand. If it forms a loose mound when you squeeze
gently, but crumbles when you squeeze harder, you’ve got
good garden loam.
Old-time gardeners used to taste their soil to find out
whether it was acidic or alkaline. If the soil tasted sour,
it was acidic; if bitter, it was alkaline. If it tasted
sweet, it was just right. You don’t have to eat dirt to
test your soil’s pH. You can buy a pH test kit, or you can
shake a tablespoon of dry soil and a tablespoon of white
vinegar together in a jar small. Put the jar to your ear.
If it fizzes, your soil is alkaline. If the fizzing is
weak, or you hear nothing at all, clean the jar and put in
another tablespoon of soil. Add a few drops of ammonia and
fill the jar two-thirds full with distilled water (you can
use rain water if you’re sure it isn’t acid rain). Set the
jar aside for a couple of hours. If the water turns dark,
your soil is acidic.