A soil amendment is any material added to a soil to improve its physical properties. The goal is to provide a better environment for roots. After all, gardening is all about plants that are supported and fed through their roots.
On clayey soils, soil amendments improve the soil aggregation, aeration, drainage and rooting depth. On sandy soils, soil amendments increase the water and nutrient holding capacity.
Soil amendments are typically animal or plant based. Animal-based amendments contain manure and are readily available bagged or in bulk. These should be used with caution, limiting the application rate, due to the possibility of high salt content, which can burn roots. Application rate for animal-based amendment is 1/2 to 1 inch. Caution should be used with edible crops.
Plant-based amendments may be applied at a higher rate, up to 3 inches. All amendments should be thoroughly mixed into the soil at root level (6 to 8 inches deep.) In the soil, macro and micro-organisms decompose the amendment, using it for energy and reproduction Plant nutrients are produced and taken up through the roots of the plant. Decomposition of soil amendments requires water, so in drier soil, decomposition occurs more slowly. For more information about soil amendments, go to https://extension.colostate.edu/topic-areas/yard-garden/choosing-a-soil-amendment.
In contrast, mulch is spread on the soil surface, much like a blanket. It is useful in reducing evaporation and runoff and inhibiting weed growth, as well as making the garden look nice. It can also regulate soil temperature and compaction.
Bark mulch is sold in different sizes. The larger the particle, the longer it takes to decompose and will not need to be replaced as often. The smaller particle mulch, such as a light or dark humus, will decompose faster.
Rock can also be applied as a mulch. Some plants thrive from the heat created from the rock. Ice plant seems to thrive under rock mulch. You can count on weed seed germination in a rock mulch environment.
For mulch to be effective, it needs to be 3 to 4 inches deep. Whether you plan to purchase soil amendments or mulch at a local landscape yard, you’ll need to know the square footage of the area you want to cover and the depth of the application. This will be translated into the proper bulk amount to be purchased.
In the vegetable garden, you might use dried grass as a mulch. It will achieve the same result and will eventually decompose into the soil. There are many types of mulch and as many situations in which they are used. For more information about mulches, go to https://extension.colostate.edu/topic-areas/yard-garden/mulches-for-home-grounds-7-214.
The El Paso County Extension is operating remotely due to COVID-19. Submit gardening questions by email at firstname.lastname@example.org.