Understanding Soil & Its Function

The function of soil is to anchor plant roots and provide water, air and all nutrients to plants to support growth.

The function of soil is to anchor plant roots and provide water, air and all nutrients to plants to support growth. Soil is made up of weathered rock and mineral particles, like clay, sand and silt, and organic matter which is composing animal and plant material plus microorganisms.

The addition of organic matter, like compost, improves the structure and workability of any type of soil. Instead of a compacted soil with small-sized pores, the addition of organic matter creates larger clumps that form large-sized pores for better water and air movement. Organic matter improves sandy soil by helping it retain water and nutrients for plant roots.

Pore space is the area between the solid particles in soil. These spaces are either water or air-filled and allow the roots to grow. The larger the mineral particles, the more large-sized pore spaces there will be. Thus, sandy soils have lots of large pores and clay soil has smaller pore spaces. Soils need a balance of large and small pore spaces. Large pores let water flow through and tend to be air-filled, while small pores hold water for plant roots to access.

Soils are classified by the type of mineral particles they are made of. There are 3 types of soil particles: sand, silt, and clay. Soils are usually a combination of two or more of these types of mineral particles. Sand has the largest particles and large pore spaces. Sandy soils drain quickly and have low soil nutrition. If you look closely at a sandy soil, you can see the individual particles. On the other hand, individual clay particles are microscopic. Clay soils have particles that pack together tightly, so they have small-sized pores. It drains poorly and holds a lot of water. Silt soils have particles and pore spaces that fall in between sand and clay.

You can quickly and easily figure out your soils texture by doing the feel test. Moisten a tablespoon of soil and roll it into a small ball. If the ball packs together and is moldable, your soil contains clay. If you can form a 2-3 inch ribbon with your ball of soil, you have a high clay content. If the ribbon falls apart, or feels gritty, you have a mix of clay and sand. If the soil ball will not hold together regardless of how much water you add, its a sandy soil. It will feel gritty.

A favorable soil texture will hold its shape when gently squeezed and will only crumble if squeezed hard. Even if your soil has a favorable texture, it will still benefit by mixing in Miracle-Gro® Soil Improvements, because adding organic matter can further improve even ideal soils.