The ideal garden soil is deep, friable, well-drained and high in organic matter. Proper soil preparation provides the basis for good seed germination and subsequent growth of plants. Managing soils for optimal plant growth is an ongoing process that consists of proper tillage, adding amendments, and proper fertilization and irrigation.
Soils in Idaho vary widely due to topography, climate, and origin. In southern Idaho, most soils have a high pH (alkaline) and contain very little organic matter. These soils may need extra applications of phosphorus and micronutrient fertilizers and should never be amended with lime or wood ash.
Northern Idaho soils can have a relatively low pH (acidic) and contain considerable organic matter. Some of these soils may need the pH adjusted upward with lime.
In either location, soils can vary in texture from sand to clay. The pH of soil is important in determining which nutrients will be readily available to plants (see illustration at left). Sandy soils need constant addition of organic matter, frequent and light applications of water, and constant fertilization. Clay soils may need to be amended with organic matter and/or soil amendments to improve water penetration. It is important to know the characteristics of your soil in order to design an appropriate management plan.
Regardless of soil type, careful use of various amendments can improve soil and provide the best possible starting situation for your plants. The best amendments provide organic matter and consist of manures, composts, peat moss, crop residues, grass clippings, green manures, bark, wood chips, straw, or any number of other materials. The type of amendment chosen is dictated by availability and cost.
Before fertilizing or tilling, it is best to get the soil tested for nutrients, pH and organic matter. Several labs, both university and private, will test your soil for a fee. Once you determine fertilizer needs, broadcast fertilizer evenly on the soil surface and till it in. Make sure the soil is not too wet during cultivation to avoid compaction.
It is important to understand that most plants’ nutritional needs are supplied by the soil. Consequently, proper soil preparation will go a long way toward achieving a successful garden.
For more information on soil preparation, see the brief, but excellent Utah State University publication, Preparing Garden Soil.
Washington State University provides a comprehensive guide to soil management.