Soil has texture and structure. Texture is the size of the sand, silt and/or clay particles that make up a soil. Grand County largely has clay soils, which has a very fine texture like sticky flour. Clay soil is nutrient rich and retains moisture but drains poorly and compacts easily. Structure is how soil particles fit together. Soil with good structure is loose and crumbly and you can easily push your fingers into it. It has many empty spaces (pores) between soil particles for air, water and nutrients to circulate and for roots to easily grow. Soil fertility is the natural presence of the essential nutrients nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, zinc, molybdenum, manganese, boron, copper, cobalt, and chlorine that are needed for plant growth. Soil PH is a measurement of a soil’s acidity or alkalinity. In Colorado the majority of our soils are alkaline but are in an acceptable range for most plants. Soil also naturally contains an enormous and diverse number of living organisms including bacteria, fungi, protozoa, nematodes, insects, spiders, mites and earthworms. Let’s call them “soil critters”. They eat the dead cells and tissues from plants and other soil critters and turn them into nutrients, energy, carbon dioxide and water to support plant life. So gardeners need to feed and nurture their soil critters.
The best way to get loose, crumbly, fertile garden soil that feeds its soil critters is to add organic matter once annually in the spring. Organic matter is material from formerly living plants and animals in various stages of decomposition. Adding organic matter to soil is called “amending” the soil. Soil amendments include: compost, sphagnum peat, aged or composted animal manure (never fresh!), composted sewage sludge, chopped straw, aged sawdust, dried grass clippings and shredded dry leaves. Compost is the gold standard for adding organic matter to vegetable gardens. It is the product created by the breakdown of plant and/or animal wastes through the controlled manipulation of high heat and moisture. It can be homemade (a challenge in Grand County due to average low temperatures and moisture) or commercially produced and sold in bags at garden centers. Compost from animal manures has a high salt content so it is better to use an all plant compost or a blend of plants and animal manures. For the first 3 years of a new vegetable garden distribute 2-3 inches of compost on top of the bed and turn it into the top 6-8 inches of soil. Thereafter reduce the amount to 1-2 inches per year.
Gardeners are often confused by the difference between compost and fertilizers. A fertilizer is a soil amendment (liquid or granular) that by law guarantees the products percentage of the primary nutrients nitrogen (N), phosphate (P) and potassium (K), which if added correctly, helps plants grow. Fertilizers supplement the nutrients naturally occurring in soil. By law compost is not a fertilizer but acts as one since activity by soil critters slowly releases nutrients from the compost. Fertilizers may be organic (from natural sources) or synthetic (chemically manufactured). Plants can’t tell the difference between natural or synthetic nutrients. The difference is in the speed of nutrient uptake. Synthetic fertilizers, such as Miracle-Gro, are immediately available to plants. Organic fertilizers are slow (months to years) because they first must be processed by soil critters. However, such patience is a virtue. Relying solely on synthetic fertilizers will not help your soil develop into the healthy living ecosystem necessary for a sustainable vegetable garden. It is okay to sometimes use a combination of organic and limited synthetic fertilizers.
A few more pointers for good garden soil management are: (1) Avoid over-tilling. You disturb the work of soil critters. Turn soil once in the spring to breakup winter snow compaction, add organic matter and prepare the seedbed; (2) Do not work soil when wet! It will compact! To test soil moisture, squeeze a moist ball of soil. It should easily crumble in your hand; (3) Protect soil from compaction. Do not stand, sit, kneel, or walk on prepared soil and; (4) Raised beds require better than average soil due to plant density.