Q. Some seed packets say to plant “as soon as the soil can be worked” in the spring. How can I tell when that is? What happens if I start too soon?
A. Besides the danger that some seeds planted in cold soil will rot rather than grow, starting “too soon” actually poses a greater risk to the soil in your garden than to any seeds you plant early in the spring. Digging, tilling, and walking on soil that is still wet from melted snow or spring rains can damage its structure in ways that will haunt your efforts for the rest of the growing season.
Working wet soil destroys the pore spaces between soil particles that allow air and water to move through the soil. Large, compacted clumps of wet soil become impermeable, concrete-like clods that resist penetration by roots and moisture. Instead of soaking in, water runs off or sits on the surface of compacted soil, while a lack of air spaces limits root growth.
Take a hands-on approach to judging whether garden soil  is too wet, too dry, or just right for digging: Pick up a handful of soil and squeeze it gently into a ball. Then apply light pressure to the ball with a finger from your other hand. If the ball breaks apart easily into loose pieces, the soil is dry enough to dig. If pressing on it flattens the ball or breaks it into large chunks, the soil is too wet—wait a few days and test it again.
Soil that won’t hold together when you squeeze a handful is too dry. Working dry soil also damages the structure by reducing it to dust. If your soil is too dry to form even a loose ball, set a sprinkler to soak it deeply and thoroughly. Then wait a couple of days and test to see if it has dried enough to be safe to work.
Originally published in Organic Gardening Magazine, April/May 2012