That's a no-brainer, to be sure. But consider this. In an era when levels of hazardous pollutants are rising alarmingly worldwide, our Arizona soil continues to maintain a shockingly healthy profile.

It must be all that dry heat. Or the fact that the soil in Phoenix is composed mainly of clay, with large deposits of calcium carbonate, which makes it highly alkaline and, therefore, generally great for planting. That's the good news; the bad news is that calcium carbonate also forms layers of rock-hard caliche, making it impossible to dig a hole in many parts of town. (Ever wonder why there's so little underground parking here? Or why so few houses are built atop basements?)

Plants don't care about parking, though; what they really want is water. Because our lower desert soil is often high in iron (a chemical typically unavailable to plants, which like a drink that's lower in alkalinity), and our water is fairly alkaline and salty, it's not a bad idea to mulch the heck out of your topsoil before planting a temperamental tiger lily (or whatever), to create a better-balanced soil that quenches a plant's thirst for lower-pH water.

Because Phoenix's dense clay soil packs together tightly, becoming like soup when it's wet and preventing proper soil aeration, green thumb gardeners recommend making the soil around a plant more permeable to air with a bagful of large-grained sand to improve aeration. Ironic, isn't it? Adding sand to the soil of the desert. But there you go — another thing about Phoenix that doesn't make a heck of a lot of sense.

To see an illustrated infographic of caliche, visit www.phoenixnewtimes.com/bestof2011.