Garden publications often focus on soil fertility, defined as the levels of major and minor nutrients available to growing plants. But another aspect of soil is extremely important, especially for the home gardener: tilth, which refers to the soil's physical condition. Hard, crusted soil is an example of poor tilth.
Benefits of Good Tilth
Soil of good tilth is beneficial for both you and your garden plants. Proper physical condition allows for faster germination, reliable seedling emergence and easier root penetration. Good tilth also provides larger pore spaces that promote proper soil aeration and moisture retention. Gardeners appreciate soil of good tilth because it is pleasant to work with -- sowing, transplanting, weeding and cultivating are all easier in soft, moist, crumbly soil.
Perhaps the most common form of poor tilth in the home garden is hard, crusted soil. Several factors contribute to this problem, and it is important to determine your particular causes so you can fine tune your remedies. Soils with a high clay content tend to get hard, and so do poorly drained soils that repeatedly get soaked then baked by the sun. Excessive rototilling can break down soil aggregates, which are essential for good tilth. Soil readily becomes hard when subjected to compaction from such things as vehicles, carts and even feet.
If you have clay soil, you can add sand to your soil in an attempt to lower the overall proportion of clay. This approach is impractical for larger gardens, though, because it might take an enormous amount of sand to make a noticeable difference. The soil amendment known as gypsum (hydrated calcium sulfate) loosens clay soils and reduces crusting by promoting soil aggregation. If poor drainage is contributing to your hard soil, try planting deep-rooted cover crops such as sweet clover, alfalfa or oilseed radish. Minimize rototilling, and never till the soil when it is wet Soil compaction is sometimes unavoidable, but you can avoid the ill effects by planting in wide beds and confining traffic to the rows between beds.
In any case of hard soil, the first and most fundamental remedy is to add organic matter -- compost, manure, crop residues, peat moss and lawn clippings are all excellent. Organic matter improves tilth directly by binding small soil particles into aggregates and indirectly by feeding soil organisms that alter the physical condition of the soil. Minimize the use of pesticides, which are often harmful to these same beneficial soil organisms.