With Saturday being Earth Day and all, I thought this might be a good time to talk about earth. Not the planet Earth; just plain ol' lower-case earth.

Have you been treating your dirt like dirt? So many of us never give the earth beneath our feet a second thought. Admittedly, it's not a terribly glamorous topic; in fact, soil gets little or no respect in the media, often being portrayed as something bad, or "dirty."

And that's just unfair. Because if we didn't have dirt, who would grow our fruits and vegetables and flowers for us? It's a dirty job, but somebody's got to do it.

The soil feeds the plants that feed us. Ideally, we return the favor by adding compost, manure, and other natural soil amendments to the dirt to maintain its fertility.

Why, you ask, does it matter whether or not we replenish our soil with organic matter? I'm so glad you asked, because that's a really important question.

In Collapse: How Societies Choose to Fail or Succeed, Pulitzer Prize-winning author Jared Diamond cites abuse of the soil as a precursor to a civilization's collapse. It's a form of ecocide.

Relying on chemicals may seem like an efficient way to boost plant production, but in the long run, it depletes the soil and launches a vicious cycle in which plants require endless doses of synthetic fertilizers to make up for the soil's lost fertility. Plants grown this way are also more vulnerable to pests and disease than organically grown plants.

Healthy soil is a living, breathing thing, full of tiny microorganisms. When you douse the earth with chemicals, you're actually killing off these beneficial creatures. In other words, you're severing a link in the food chain, which throws everything out of whack, eventually.

I knew nothing about all this when I first started growing a few flowers and tomatoes on my Manhattan roof. I bought the same fertilizer that everyone uses, the one that's most widely sold; the ubiquitous Miracle-Gro.

I used Miracle-Gro faithfully on my plants, and the results were sufficiently miraculous. Matt and I marveled at the strong, sturdy-stemmed cosmos and prolific tomato production that Miracle-Gro gave us.

At some point, though, I started to wonder; should the stems of my cosmos be as thick as a baby's forearm? The more books I read about gardening, the more I realized that I was making a terrible mistake.

In retrospect, the color should have tipped me off. Miracle-Gro is a deep turquoise-colored powder. This is not a color found in nature.

A good, all-natural, 100% organic fertilizer should be brown, really; the color of manure. After all, that's what the best fertilizers consist of. There's cow manure, chicken manure, rabbit manure, even a brand of fertilizer called ZooDoo, which combines giraffe, zebra, elephant, bison, antelope, llama, rhino, hippo and camel manures. Their motto? "Number 1 for Number 2's."

My first choice, however, is Jamaican bat guano, because it's naturally high in phosphorus, which promotes flowering and fruiting. So it's perfect to give your annuals and tomatoes a boost and keep them blooming and producing all summer long.

If you're growing greens, you'll do better with Mexican bat guano, which is naturally high in the nitrogen that greens need. If you want a single guano that's high in both nitrogen and phosphorus, you could try Peruvian seabird guano. There's a guano for every kind of garden.

So toss the Miracle-Gro, and get yourself some guano. It won't save the planet, but it will spare your own patch of earth the indignity of being drenched by turquoise-colored toxins.

Jamaican Bat Guano

Why We Like It: An all-natural boost for flowering & fruiting plants

Cost: 2.2 lbs $7.95

Where to Buy It: Amazon