Organic soil amendments improve the ratio of organic matter in the garden bed. Microorganisms, insects and earthworms feed on organic matter, improving soil texture and nutrient availability. Plants readily access water, air and nutrients from soils rich in organic matter. Test soil pH levels in your garden before choosing soil amendments.
Well-rotted herbivore or poultry manure is safe to use on food crops when it is thoroughly composted to kill pathogens. Allow 40 lbs. of composted manure for every 100 square feet of soil surface. Dig into the soil to a depth of 6 to 9 inches. Avoid composted manure in garden soils already high in salt levels.
Sphagnum peat is grown in renewable bogs in the northern U.S. and Canada. Its low, or acid, pH levels lower alkalinity and improve water-retentive qualities of sandy soils. Apply peat over the bed in a 1- to 6-inch layer and dig in deeply. The higher amount requires deepest tilling. Peat moss left on the surface prevents water penetration.