|Gardens start with dirt|
The measure of a substance’s acidity or alkalinity is called pH—little “p,” big “H”—standing for “percent of Hydrogen.” The pH scale runs from zero to 14, but actually starts in the middle, at number seven, or neutral. Seven to zero is the acid end of the scale, seven to 14 alkaline, or basic. The progression between numbers is geometric: four is ten times more acid than five, nine is ten times more basic than eight. Vinegar tests out to about pH 3; chalk’s about a pH 12.
It matters because soil pH values influence how plants absorb nutrients, which translates to how well a given plant will perform in a given place. By way of illustration, let’s talk iron absorption. An essential micronutrient, iron is most readily available to plants rooted in soils with pHs between 4.0 and 6.5. If pH is higher than 6.0, iron absorption is curtailed. You can pour all the Ironite® around you want—the plant can’t take it in. Most soils contain sufficient iron, but that’s a moot point if the pH is too high. Iron deficiency frequently manifests as chlorosis, characterized by yellow leaves with green veins.
Many other nutrients are absorbed better at lower pHs as well; optimum absorption of most nutrients occurs at pHs from 5.0 to 7.0. (See table.)
|(Click on the table to enlarge it)|
Don’t believe me? Get a soil test. Get a soil test even if you do believe me. Call your local Cooperative Extension Office to find out how. They may also be able to translate for you when you get the results. (Maybe not, in North Carolina. Tim and I had to take a seminar before we were able to decipher all those symbols and figure out what they told us about our yard.)
What do you need to know in order to optimize plant performance in the soil you do have? Just because it’s more common, let’s start with sand.
|My yard: sand to China|
Despair not: both soil types make fine gardens with some amending. Both lack high (or even moderate) levels of microbial activity, but you can give the little critters a boost by adding generous amounts of composted organic materials. Why do I want to do that? you ask. Because good soil is, by definition, alive, full of organisms including the ones we can see, like worms, centipedes, ants and slugs, as well as the ones we can’t: bacteria, fungi, nematodes and protozoa.
Ewww, you say, but since I need them, where do I get them? I told you already, composted organic materials. You can produce your own, simultaneously reducing overcrowding in our landfills, by composting your food waste and yard debris. Keeping small herds of bovines, ovines or equines and flocks of chickens, turkeys or bats would be nice, too—less packaging—but many communities frown upon urban farming.
|Not all commercial composts|
are created equal:
read the label
1. When you want to create new planting beds from lawn or natural areas and don’t feel up to digging them out by hand, consider this method: place a layer of newspaper six to ten sheets thick over the unwanted vegetation. Cover the newspaper with organic mulch three to four inches thick. Go do something else for three or four seasons. (Have I mentioned that gardening is not the best of hobbies for personalities requiring instant gratification?) Light deprivation discourages the growth you want discouraged while the newspaper and mulch biodegrade, enriching the soil.
2. Be careful about amending with topsoil. “Topsoil” is a vague catch-all sort of word meaning something like “the stuff scraped off the top of something.” One lady we know wanted to transform her flat back yard into an undulating landscape, so she bought ten double-truckloads of what the seller assured her was "topsoil” and had it sculpted into a lovely rolling berm. When everything she planted the first season only survived long enough to get really ugly before dying, she had the “topsoil” tested. Well, it may indeed have been scraped off the top of something, but mostly it was home to nematodes of the most unbeneficial kind. The lady subsequently spent four years, pots of money and untold hours outside sweating and swearing under her breath to remediate the damage. Less horrendous but still not good, another friend paid good money for a load of “topsoil” that arrived chock-full of asphalt chunks. When it comes to “topsoil,” caveat emptor.
detrimental to soil bacteria
|A Southern Living garden spread|