|The Dirt on Soil|
By Marie Iannotti
Soil is often viewed as the boring part of gardening. While garden soil will
never be glamorous or even as interesting as choosing plants, there is a whole
world under our Wellingtons that literally and figuratively is the foundation
for our gardens. New gardeners are cautioned to put money and effort into
improving their soil before they even consider planting, but few appreciate the
wisdom in what they are hearing until they watch their new plants struggling for
survival and demanding more and more food and water. In organic gardening, you
learn to feed the soil and let the soil feed the plants.
The soil found in a typical yard will be about 90% mineral residue and only
about 10% decayed organic matter. Yet it sustains a community of insets and
microorganisms. The reason for adding additional organic matter to your soil is
to provide food for the beneficial microorganisms that release nutrients into
the soil as they decompose the organic matter. Earthworms and other soil
dwelling insects aerate the soil as they move through it and contribute still
more organic matter with their waste and decomposition. This makes for what is
called healthy soil.
Pesticides sprayed on the plants will make its way into the soil and can kill
the insects and microorganisms living there. Synthetic fertilizers contain salt,
which can also kill the soil's residents as well as build up in the soil and
cause harm to the plants you are feeding. And synthetic fertilizers add nothing
to the soil's fertility.
What is Healthy Soil?
When discussing soil, we generally focus in on four things: texture, structure,
pH, organic matter and fertility.
Soil texture refers to the size of the soil particles.
Sand: Sand has the largest particles and they are irregularly shaped. This
is why sand feels course and also why it drains so well. Sand doesnít compact easily.
Silt: Silt particles are much smaller than sand, but still irregularly shaped.
Clay: Clay has microscopic sized particles that are almost flat. Clay packs
very easily, leaving little to no room for air or water to move about.
Sandy Loam: Sandy loam is considered the ideal garden soil and consists of a
mix of the three basic textures. However, donít run out to buy sand to add
to your clay soil or vice versa. Mixing sand and clay will give you cement.
Thereís more to the equation than just balancing soil textures.
Soil structure refers to the way soil clumps together. You can usually
determine what your texture is by testing your structure. Squeeze a handful of
damp soil into a ball in your hand. If you poke the ball lightly with your
finger and it breaks apart, it is probably sand. If a bit more pressure breaks
it, youíre dealing with silt. If it sits there despite your poking, you have
mostly clay. Do determine a more accurate reading of the percentage of each
texture in your soil, try this easy experiment. (Add link to jar test)
A good soil structure is crumbly. This allows plant roots to work their way
through it, air can pass through and water drains, but not so quickly that the
plants canít access it. If youíd like to test how well your soil drains, try
this experiment. (Link to drain hole test.)
There are two basic ways to improve soil structure and they work in tandem.
Soil dwelling insects. As mentioned earlier, insects moving about in the
soil help to aerate the soil and they add small amounts of organic matter,
the second structure improver.
Organic Matter. Organic matter improves any type of soil. Compost, leaf
mold, manure and green manures are all decaying organic matter. They loosen
and enrich soil and provide food for the soil dwelling insects.
You can loosen soil structure by tilling and sometimes this is necessary.
But tilling can over crumble soil and it kills the insects living there. So
regular tilling is not the best option.
Soil pH is a measure of your soil's acidity (sourness, a measure of below 7.0)
or alkalinity (sweetness, a measure higher than 7.0), with 7.0 being neutral.
Most garden plants prefer a pH in the neutral range. Some plants are more
specific in their requirements. Lilacs and clematis thrive in sweet soils.
Rhododendrons and blueberries like a lower pH. You can adjust the pH in
different parts of your landscape.
Generally speaking, if your plants are growing healthy and well, your pH is
probably fine. If your plants are having nutrient problems or are not growing
vigorously, itís worth it to test your pH. If the soilís pH is not within an
acceptable range for the plants you are growing, the plants will not be able to
access the nutrients in the soil, no matter how much you feed them.
You can buy many types of pH testers in a garden center. You can also bring a
sample into your local Cooperative Extension office, to be tested for a nominal
fee. Once you know what your pH is, you can begin to adjust it slowly. You add
some form of lime to raise pH and a form of sulfur to lower it. What type and
how much depends upon your soil and test results. Your Extension report and most
testing kits will tell you what to do once you get your results.
Adding lime or sulfur to alter soil pH is not a quick fix. It can take months to
register a change in the pH and you will need to periodically retest your soil
to insure it doesnít revert to its old pH. It is sometimes easier to simply
change your plants to suit your pH.
Organic matter does so many wonderful things for a garden, itís just silly not
to take advantage of it. There would be no organic gardening without organic
matter. Decaying organic matter is how plants are fed in nature. Unfortunately
weíve become very tidy landscapers and we tend to remove any dead plant material
that falls onto our lawns. It would be so much more beneficial to allow the
fallen leaves to blow off into the bushes, where they will not only feed the
soil, they also prevent erosion and mulch the soil.
Organic matter added to garden soil improves the soil structure and feeds the
microorganisms and insects. The more beneficial microorganisms your soil can
support, the less bad organisms will survive. The good guys feed on harmful
microbes like nematodes and certain soil born diseases. They also release their
nutrients into the soil when they die. So the more beneficial microorganisms
that are in the soil, the more nutrients will be in the soil. And many types of
organic matter add still more soil nutrients to the mix.
Organic matter also contains acids that can make plant roots more permeable,
improving their uptake of water and nutrients, and can dissolve minerals within
the soil, leaving them available for plant roots.
Types of Organic Matter
Compost is the poster child of organic matter. Compost is any kind of decayed
organic matter. You can make your own or buy it by the bag or truckload.
Finished compost looks like rich soil. Itís dark and crumbly with an earthy
smell. By the time the compost cooking process is complete, weed seeds, fungus
spores and other undesirable elements that may have gone into your compost
bin, should no longer be viable. Compost can be added to your gardens at
anytime, either turned into the soil or used as a mulch or top dressing.
While it is advised that you keep perennial weeds, pesticide treated material
and diseased plants out of your compost bin, most every other form of plant
material is fair game.
Garden Waster (from weeding, deadheading, pruning...)
Manure Aged animal manure is an organic material with an added bonus of soil
nutrients. Animal manure must be aged for 6 months to a year, before it is
applied to the garden. Fresh manure will burn your plants, may contain
bacteria that can cause illness from contact and it stinks. You can add fresh
manure to a compost heap and let it age there.
Cow, sheep and chicken manure are the most popular varieties, but there are
several more. The manures to avoid because of their disease potential for
humans are: cat, dog, pig and human manures.
Green Manure Green manures are basically cover crops that are grown with the
intention of turning them back into the soil. Obviously this would be more
useful in the vegetable garden or in a newly created bed where tilling will
not harm existing perennial plants.
Different green manures offer different advantages. Some, like alfalfa, are
grown for their deep roots and are used to breakup and loosen compacted soil.
The legumes, clover and vetch, have the ability to grab nitrogen from the air
and eventually release it into the soil through their roots. If allowed to
flower, clover especially is attractive to pollinators and beneficial insects.
All green manures will suppress weeds and prevent erosion and nutrient runoff
in areas that would otherwise be unplanted. And they all assist with creating
good soil structure and food for the microbes, once they are tilled in and
begin to decompose.
Popular choices for green manure include: annual ryegrass. barley, buckwheat,
clover, winter wheat and winter rye.
The nutrients in your soil are the final component in building healthy soil.
Just like people, plants need certain nutrients to grow and to fend off disease.
Organic fertilizers can be made from plant, animal or mineral sources and are
basically returning what was taken from the soil. Organic fertilizers are
released slowly, which means that plants can feed as they need to. There is no
sudden change in the makeup of the soil which might harm the microbial activity.
Building healthy soil is an ongoing process. By making healthy soil a focus at
the start of making a garden, you will have a head start on creating a
sustainable organic garden.