Here's an easy test to see whether you need to improve your soil. Take a round-headed shovel, place its tip on the surface of your planting bed, jump high into the air, and stomp with your feet on the blade's flat end. If you briefly lose consciousness, as well as some fillings, your soil could use some improvement.
Rock-hard soil could mean a couple of things. You could be digging in rock. Most likely, though, you're dealing with dirt that has lots of clay in it.
Clays of Many Colors
Folks in the Southeast often curse red clay, but clay comes in lots of colors--black, brown, white, and even blue. No matter the color, it is tough on plant roots. When clay is dry, it's as hard as concrete. When wet, it's as sticky as taffy. Clay drains poorly, which leads to rot, and contains little air, which suffocates roots. If you want plants to grow, you'll have to amend the soil.
What's the best way? Some people claim you can loosen clay by adding gypsum (calcium sulfate) to it. The theory is that gypsum binds clay particles together to make bigger particles, providing more space for air, water, and roots. While this works to some extent, adding gypsum alone isn't enough for most gardens. The best way to loosen and improve clay soil is by adding lots of organic matter.
Breaking It Down
Organic matter consists of the decaying remains of plants and animals. It does a good job of binding clay particles together (better than gypsum). This results in improved drainage and aeration as well as sofer and lighter soil. It also increases the soil's fertility while creating a friendly environment for beneficial soil microbes and earthworms.
How much organic matter should you work into your soil? In most cases, the answer is as much as you can. It comes in many forms. One of my favorites is the leaves and pine needles that fall from trees in autumn. I shred them with a mulching mower and then either till them into the ground or lay them atop the soil as mulch. They do a great job, and you can't beat the price--free.
Other good sources of organic matter are composted cow manure, garden compost, and ground bark (add a little nitrogen fertilizer in with the bark to help it break down). And if you need to both acidify and loosen the soil, nothing works better than baled sphagnum peat.
Soft Soil at Last
Don't expect overnight results. Because plants, microbes, and earthworms break down organic matter, you'll need to add more next year. But eventually, you'll have that rich, soft soil you've always dreamed about. And you won't lose any more fillings.
It Helps Sand Too
Sand seems like the opposite of clay. It's so loose that water and nutrients pass straight through it, leaving plants thirsty and hungry. Know how to fix this? Amend sandy soil with lots and lots of organic matter.
"Secret to Perfect Soil" is from the May 2004 issue of Southern Living.