When to work the soil
Working the soil too early is a mistake. When the earth is still saturated with melting snow or spring rain, it is easily compacted by treading across it, or even worse, driving heavy equipment on it. In addition, large clumps of wet soil turned over at this time will only bake into impervious clods that will be very difficult to break up later. Plant roots grow best when there are some air spaces between soil particles. Heavy, wet soil doesn't break up into the loose, air-retaining texture that is best for plants. Its clumpy texture is also likely to trap pockets of air around plant roots, and that is just as bad as no air.
How can you tell whether your garden has dried out enough to be worked? The truest test of soil condition is that age-old gesture of the gardener—fingering a handful of soil. Pick up about half a cup of earth in your hand. Now squeeze the soil together so that it forms a ball. If the ball of earth can readily be shattered by pressing with your fingers or dropping it from a height of 3 feet or so, it is dry enough to dig. If the ball keeps its shape or breaks only with difficulty into solid sections rather than loose soil, it still contains too much water. Clay soil that is too wet will feel slick when rubbed between thumb and forefinger. If it is very wet (75 to 100 percent moisture), the mass will be pliable, and a ribbon of earth can be drawn out and pressed with your finger. Working soil that wet can spoil its texture for the whole season.
Heavy clay soil will form a ball even when moisture content is less than 50 percent. Soil that is somewhat coarser, a sandy loam or silt loam, tends to crumble when moisture content is low but will probably form a ball at about 50 percent. At 75 to 100 percent moisture, it will be dark, pliable, and may feel slick between the fingers. Coarse-textured sandy soil will not form a ball if moisture content is below 50 percent. At 75 to 100 percent moisture, it can be pressed into a weak ball, but even then it shatters easily. Coarser soil, of course, may be worked at a higher moisture content than fine-particle clay.