Basically all types of soil will benefit from the addition of organic matter. Check out the following tips to learn about adding nutrients to improve your soil and ultimately encouraging better plant growth. Add a thick layer of mulch and let it rot to improve the soil of existing gardens. Minerals, released as the mulch is degraded into nutrient soup, soak down into the soil and fertilize existing plants. Humic acid, another product of decay, clumps together small particles of clay to make a lighter, fluffier soil.