The information for this article comes from the MSU Master Gardener Volunteer Class.
Often, when people have difficulty growing plants, they
forget to consider their soil. They
will say, “Well, I gave it plenty of water!
There’s plenty of sun! I dumped
some fertilizer on it! I don’t see any
insects! I don’t know what’s wrong...”
This person may seem to have been on the right track when
they said that they “Dumped some fertilizer on it.” But did they add the right amount or type of fertilizer? What about the soil texture? Is the soil loose enough for the roots to
grow? Is there enough living matter in
the soil? Is the soil pH right for the plant?
To have a healthy garden, the composition of the soil needs
to be right for the plants in the garden. So... LET’S PIMP YOUR SOIL!
Soil Texture:
The ideal composition of soil should be: 45% mineral, 5%
organic, 25% water and 25% air.
There are 3 basic types of soil: sand, silt and clay. Sand has the largest particle size and clay
the smallest. Sand drains well and
dries out quickly. Clay clings to
moisture and can become thick and difficult to dig through.
 | |
| Sandy, gravely Michigan soil can be seen between the rows on this Romeo Farm. |
You might think that you can improve either type of soil by
simply mixing sand and clay together. DO NOT DO THIS! You will end up with cement!
Instead, add organic matter. You
may have to do this every year until you build up a nice layer of topsoil. Organic matter is most readily available in
the form of compost, leaf mold, peat or animal manure. Combine the organic matter with the soil by
hoeing it in. You can also use a
tiller, but be careful not to over-till.
When you till, leave clumps. Do not create an even powdery soil, or the
soil will either wash away or compact back into cement. Also welcome earthworms to your garden. These invertebrates will carry organic
matter down into the native soil for you.
A healthy soil with enough organic matter will be dark in
color – almost black. It will hold
together if you squeeze it tight, but will crumble again if you gently tap it
or push at it with your finger.
Organic matter also encourages living things to make a home
in your soil. These include bacteria,
fungi, mycorrhizae, lichens, protozoa, invertebrates, and vertebrates. May of
these organisms help to keep the soil fertilized, help to break down organic
matter and some even have symbiotic relationships with the plants in the
garden. Remember, healthy soil is
living soil!
You can buy organic matter at your local nursery or super
store. You can also make it yourself by
composting. Simply keep and contain
your food scraps, grass clippings, and leaves in a bin or pile. If you want to speed the composting process,
turn the material over with a shovel or spading fork once in a while. This material will break down and will be
ready to apply to your garden when it looks like crumbly black soil.
For the sake of health safety, do not add meat, pet manure
or human manure to the compost pile.
These may contain unhealthy bacteria that can cause sickness when
applied to vegetable gardens. Pet and
human manure are not considered useful as compost until they have broken down
for at least 10 years. Most of us
cannot wait that long!
Most soils can be improved enough to grow plants well simply by adding organic material to improve soil structure. So, always add organic matter to improve the soil first. If you have tried this, and your plants are still struggling, please read on.
 |
| Dark soil under this rose is high in organic matter. |
Fertilizer and Plant Food:
Sometimes people think that fertilizing is the only way to
improve soil, and the more the better!
NOT TRUE!
You cannot just dump fertilizer on a plant and expect it to
grow. Different plants require
different amounts of nutrients. Also,
the soil contains most of the nutrients that a plant needs. It is possible that your soil is lacking in
a particular nutrient, but do you know which one?
To find out, get a soil test! You can send soil to your local extension office. They will return a report to you that states
exactly which nutrients your soil contains, and will recommend an amount and
type of fertilizer for you. If you live
in Michigan, you can send for a soil test here: http://msusoiltest.com/
There are 17 mineral nutrients that plants typically
require. These are: Hydrogen (H),
Oxygen (O), Phosphorus (P), Potassium (K), Nitrogen (N), Sulfur (S), Calcium
(Ca), Iron (Fe), Carbon (C), Boron (B), Magnesium (M), Chlorine (Cl), Manganese
(Mn), Molybdenum (Mo), Copper (Cu), Zinc (Zn), and Cobalt (Co).
When you get a bag of fertilizer, you will typically see 3
numbers listed on the front of the bag.
These represent the 3 most commonly required plant nutrients: N-P-K (Nitrogen, Phosphorus, Potassium). When you get your soil test results, the
report will tell you what levels of these nutrients your soil requires and how
much to apply per square foot. Please follow the directions EXACTLY! Adding
more is not better. When you add too
much fertilizer, it can just wash away into the water systems. This results in algae blooms that kill off
fish and generally pollute the water system. It also costs more to buy
more fertilizer than you need, and is of no benefit to the plants. In addition, over-use of fertilizer can
build up chemical salts within the soil and ultimately poison future plants. So, just as you would when taking medicine
for yourself, use the correct prescribed dose!
Remember the old saying, “Enough is enough, and too much is
poison!”
Soil pH:
pH is a way to measure how acidic or alkaline (base) your
soil is. If you recall from high school biology or chemistry class, 0 is the
most acidic on the scale and 14 is the most alkaline/base. Acids are generally sour in taste (lemon juice, vinegar), alkaline/bases are generally bitter in taste (baking soda). Acids and bases create chemical reactions together that result an a neutral substance and gasses (bubbles). (Remember building that volcano in elementary school buy mixing vinegar and baking soda together? No?)
battery acid
vinegar
water
ammonia
Lye
<------------------------------------------------------------------------------------------------------->
0 <----Acid 7 Alkaline/Base ---->
Neutral
You can test the pH of your soil buy purchasing a soil pH
test at any garden center. Please
follow the directions on the package exactly.
Most plants grow best at a pH between 6.0 and 7.0. However, there are a few others that
require different levels of pH. For
example, azaleas and blueberries require acidic soil with a pH around 5.0,
whereas alfalfa thrives at a neutral to alkaline pH around 6.5 to 7.5. It is important to research your plants and
to know what pH level they need to survive.
Some of the topsoil in Michigan is acidic, primarily in
areas where the soil has not been disturbed much. In suburban and urban areas, the soil is primarily alkaline
because it has been churned up by construction. Construction companies often remove the acidic top soil and pull the alkaline bedrock lime to the surface.
It is best to test the pH before choosing plants. While the pH can be adjusted somewhat within
a small area such as a raised garden bed or a pot, it is nearly impossible to change the pH of an entire
field for the extended period of time needed to grow a plant.
So, if you live in an area where the soil is acidic, do not
try to farm alfalfa or asparagus! If you
live in an area where the soil is alkaline, do not take up blueberry or
cranberry farming! Find the right site
for your growing needs.
To adjust the soil pH in a small area (for example a pot),
you can put additives into the soil.
- To make soil more alkaline you can add: lime, calcium oxide, calcium hydroxide, marl, slags, or wood ashes.
- To make soil more acidic you can add sulfur.
When adding either of these products, first test the soil
pH. Then, follow the instructions on
the product bag exactly. Again, more is
not better.
Also, you do not need to lime your lawn if your soil is
already alkaline. This will make your
grass less healthy rather than more healthy. Add only what your soil requires!
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