Garden Guru: Plant health requires keeping things in balance
By John Porter
CHARLESTON, W.Va. — Those who have taken my classes or who read this column often will know that I can get pretty insistent and preachy on performing regular soil testing for your lawn and garden.
The reason that I talk about it so much is due to its importance in maintaining both soil health and plant health.
In “The Unsettling of America: Culture and Agriculture,” Wendell Berry tells us that “the soil is the great connector of lives, the source and destination of all. It is the healer and restorer and resurrector, by which disease passes into health, age into youth, death into life. Without proper care for it, we can have no community, because without proper care for it, we can have no life.”
Most gardeners probably don’t realize that their No. 1 responsibility is not keeping their plants healthy, but keeping their soil healthy.
Soil is more than just the loose (or sometimes not so loose) crumbly stuff where you plop your tomato plants. Soil exists as a balance between minerals, organic matter, air and water.
Soil is full of life — bacteria, fungi, worms, protists and more. Soil is chemistry — elemental nutrients, ions, cations, pH and beyond.
A gardener’s true job is as the steward of the soil, whether it be in a tilled plot, a raised bed or a container.
Why test your soil?
Plants require a number of mineral nutrients from the soil in order to thrive. Six of these are considered macronutrients, meaning that the plant needs a large amount of them to survive.
The big three are the ones that you find displayed as a set of numbers on any common fertilizer bag — nitrogen (N), phosphorous (P) and potassium (K). In addition to these three, plants also need larger amounts of calcium, magnesium and sulfur.
Calcium (Ca) and magnesium (Mg) are added to soil when lime is applied (we’ll talk about why lime is important in a minute).
Sulfur (S) can come from organic matter, such as compost or composted manure. Sulfur is also present in the mineral soil itself in most of our area, since it is found in regions with abundant carbon resources such as coal and gas (since it was formed from decomposition of organic matter millions of years ago).
Plants also require seven elemental nutrients in smaller amounts, referred to as micronutrients. These nutrients are boron (B), copper (Cu), iron (Fe), chlorine (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn).
I bet you had forgot about some of those elements since your days back in chemistry class, huh?
Deficiencies in the micronutrients are not common in the garden (though they can be in container plants), as they are found in organic material. Regularly adding compost and other organic material to the garden can supply all of the micronutrients you need. It is possible, though to have deficiencies in macronutrients since plants need such large amounts of them.
We typically add the macronutrients through traditional fertilizers, like 10-10-10 or organic applications such as bone meal, blood meal, rock phosphate, fish emulsion and others.
Calcium and magnesium come from lime, though if you need to add calcium without changing pH, you can use gypsum. You can also use a little Epsom salt to add a bit of magnesium.
Another issue affecting plant health, though, is the pH of the soil. What the pH of soil does is change the availability of the nutrients to the plant by changing their chemistry. Most of these elements exist as ions or cations in the soil, and the pH of the soil affects how they are tied up to each other and to the soil itself.
For most garden plants, we aim for a near-neutral pH of about 6.5. At this pH, most of the nutrients are available at their highest levels.
This means that the plant is able to take them up and use them at a higher rate. If your pH is too high or too low, you can add all the fertilizer you want, but the plant isn’t going to be able to take it up.
Plants such as blueberries, rhododendrons and azaleas thrive on low pH levels of around 4.5, not because they necessarily prefer the acid, but because iron is available at a greater level at that pH. Turns out that these plants are heavy iron feeders.
We most commonly use lime to raise the pH if we need to bring it up to that 6.5 level. Sulfur in some form is commonly used to lower the pH. You can buy the plain yellow sulfur powder, or use a nitrogen fertilizer called ammonium sulfate if you also need nitrogen.
Getting the levels right
There’s one way to take the guesswork out of whether you have enough macronutrients and the right pH for your plants — a soil test. You can purchase soil test kits from many garden centers, but these are not necessarily accurate or specific for our type of soil.
WVU offers free soil testing for all residents of the state through our lab at the Ag Sciences building in Morgantown. To test your soil, check out Kanawha.ext.wvu.edu/agriculture/soiltest to find directions and a form, or stop by your county extension office to pick up the form.
To test, pick one specific area you would like to test and take five to 10 samples from the area, depending on how large it is.
You’ll want to take the sample from the top 3 to 4 inches for a lawn, or a little deeper for a garden. Mix all of those samples together, removing any debris, and put about a half-cup of soil into a sealable plastic bag. Mail it to the lab with your soil test form, and you’ll have results, including fertilizer recommendations, in about three weeks. Get started now — fall is the best time, and you’ll want to be ready if you plan on sowing a new lawn this fall.
This week in the garden
n Apply nitrogen to strawberries.
n Plant bok choy.
n Keep turning that compost pile.
n Soil test for your new lawn.
n Seed turnips.
John Porter is the WVU Extension Service agent for agriculture and natural resources in Kanawha County. Follow him on Facebook, Twitter at @WVgardenguru and online at wvgardenguru.com. Contact him at firstname.lastname@example.org or 304-720-9573.