My Definitions of Dirt
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Q. Regine from Braunschweig, Germany, the proud owner of "a productive allotment" (kind of like a community garden in Europe) writes: I'm a long time avid listener of your show: I know that you deem squirrels evil, you advise using BTI to keep mosquito numbers under control, you strongly promote motion activated sprinklers, raised beds, and shredded leaves. You love flame weeders. You always moan if listeners admit to using chemical fertilizer, herbicides, insecticides, or fungicides. You think that in marital debates concerning gardening that the wife is almost always right. I even know the names of your children! I LOVE YOUR SHOW. And I fondly remember back when you were the editor of Organic Gardening magazine.
"Here comes my question: After all this time I still don't know what the "yard dirt" you keep mentioning is. Also, what do you feel are good definitions of soil, topsoil, humus, and compost? Please explain! And please explain why you still recommend using peat moss."
A. Let's start with that last question. Whenever I discuss peat moss I try and make a distinction between European and Canadian peat. I would never recommend the use of peat moss to our European listeners, of which there seem to be more every day. (Keep those cards and emails coming!)
I don't think there's any argument about European peat; your native bogs were overharvested to such a dizzying degree that entire ecosystems were changed. But on this side of the pond, all of the peat moss comes from Canada, where through a good amount of research, I have come to believe the bogs are well managed and sustainably harvested. Not sure if peat moss from Canada is available in Europe, but if it is, I would not hesitate to use it. "Coir", a similar material made from shredded coconut husks is an acceptable lightweight substitute, but it doesn't provide the acidic conditions that plants like blueberries require.
We move on to 'yard dirt'. Have I ever actually used this term? I can't remember doing so, but I have also lost my car keys for the fifth time this year. Anyway, 'yard dirt' would be the existing unimproved soil on your property. It may be heavy with clay, light with sand or 'loamy', which is unlikely as loam is an excellent soil for growing things and few of us are blessed with it from the get-go.
In Europe, North America and pretty much everywhere else, existing soil could be contaminated with lead from post-war car exhausts and lead-based paints, which were banned in the States in 1978. Before that, most paints--indoor and outdoor--were lead based. A specialized soil test can tell if your 'dirt' is contaminated with lead or other bad actors. If it is, don't disturb it; just install raised beds over top of it, which you should do anyway.
"Soil": To combine a number of accepted definitions, soil is 'the upper layer of earth in which plants grow, containing organic remains, clay, sand, rock particles, minerals, gases and liquids'. As I often say, there is no specific thing as 'organic soil' although soil that has been free of chemical fertilizers and pesticides for three to five years is considered appropriate for organic farming by the various certification agencies.
"Topsoil". When purchased in bulk, this term has no accepted meaning. To hort geeks like me, topsoil is defined as the top five to ten inches (13 to 25 centimeters) of undisturbed soil, like the layer of 'duff' on an untouched forest floor. In sad reality, it is the soil that contractors removed from the area around your home-to-be and sold to their brother-in-law who will be happy to sell it back to you.
"Humus". This is a slippery one, with many varying definitions and opinions, but basically, it's the most organically rich component of soil, composed mostly of decayed plant and animal material. It is nutrient rich, drains well, retains moisture and is essential for natural plant growth. Most experts consider it to be more like the classic horticultural definition of topsoil and less like compost. But most sources agree that in general, the term 'humus' is poorly understood; and the word has no legal meaning in the soil trade.
Compost: Yay! I don't need outside sources for this one! Compost is a man (and woman) made material, created by combining a large percentage of 'dry brown' carbon-rich material (like my beloved shredded leaves) and a much smaller amount of 'wet green' nitrogen-rich material like coffee grounds, animal manures and/or vegetable waste.
Compost can be 'cold' ('pile it up and it will eventually rot') or 'hot', which means paying strict attention to the ratios, using tricks like placing a roll of wire fencing down the middle of the pile to carry oxygen to the center, and/or frequent turning. Once finished, cold compost is a good soil amendment, but hot compost, which can be finished in a matter of weeks under the right conditions, is a much more effective fertilizer and has the added capacity of preventing or controlling plant disease.
No matter what anyone tells you, you cannot make compost out of kitchen scraps alone; you just make a stinky mess. And beware of attempting to compost grass clippings; if they come from a treated lawn, the resulting compost could kill plants instead of feeding them.