The following is an article from the UT Extension Service:
Begin soil preparation by removing old plant supports, plastic mulches, excessive vegetative residues and other debris from the garden area several weeks before plantingto allow the soil to dry out. The amount of plant residue that may be turned under depends on how large the pieces are, how the garden will be turned and how long before thearea will be worked.
Long cucumber or tomato vines, for example, maybe spaded or plowed under but may tangle on the tines of a rototiller. Cover crops and thick mulch or crop residue should be turned under six weeks or more before planting.This will promote decay and reduce nutritional and insect and disease problems in the garden. Adding three pounds of ammonium nitrate per 1000 square feet of soil surfacebefore turning organic materials under will speed decay considerably.
Turning under significant amounts (an inch or more) of plant materials such as compost, organic mulches, leaves or cover crops annually will gradually increase soil organic matter content and improve most garden soils. The moisture-holding capacity will improve, as will the soil structure and nutrient-holding capability. Root penetration will improve on clay soils and soil crusting will be reduced. Garden soil should not be worked when it is too wet. Pick up a handful of soil and roll it into a ball. If the soil sticks together and does not crumble when dropped, it is too wet to work. Soil worked too wet forms large, hard clods which are difficult to break up and are completely unsuitable for a seed bed.
Soil should be worked to a depth of at least 6 or 7 inches and smoothed before planting. Seed should be planted only in moist, finely aggregated soil. Soils worked into a powdery condition are more likely to crust. Small seed planted in cloddy soil usually dry out and germinate poorly.
Source: Growing Vegetables in Home Gardens. UT Extension Service.
