Like most vegetables, beans grow best in well-balanced soil that is fertile and contains sand, silt and clay. Sandy loam soils are ideal; soil that is dominated by sand or clay can be problematic for gardeners.
Adding organic matter like compost, peat moss, manure and sawdust can improve sandy or clay soils. Clay soil can also benefit greatly from fine tilling. Coarse sand can be added to clay to improve its texture; fine sand can actually be detrimental.
Beans require soil to be well-drained, so choose a site where water does not collect after a rain. Also, do not try to work with the soil until it is dry enough -- the soil should break apart rather than stick together when you squeeze a handful of it. Beans grow best in neutral to slightly acid soil with a pH of between 6.0 and 6.8.