Is soil texture important?

Soil Excerpted from Chapter Three, Indoor Marijuana Horticulture, The Indoor Bible

Soil

Soil is made up of many mineral particles mixed together with living and dead organic matter that incorporate air and water. Three basic factors contribute to cannabis root’s ability to grow in a soil: texture, pH and nutrient content.

Soil texture is governed by the size and physical make-up of the mineral particles. The proper soil texture is required for adequate root penetration, water and oxygen retention and drainage, as well as many other complex chemical processes. Clay or adobe soil is made up of very small flat mineral particles. When it gets wet, these minute particles pack tightly together, slowing or stopping root penetration and water drainage. Roots are unable to breathe because very little or no space is left for oxygen. Water has a very difficult time penetrating these tightly packed soils, and once it does penetrate, drainage is slow. Sandy soils have much larger particles. They permit good aeration (supply of air or oxygen) and drainage. Frequent watering is necessary because water retention is very low. The soil's water and air holding ability, as well as root penetration, are a function of texture.

This cut away drawing shows how roots penetrate soil. Note there must be enough air trapped in the soil to allow biological activity and absorption of nutrients.

To check soil texture, pick up a handful of moist (not soggy) soil and gently squeeze it. The soil should barely stay together and have a kind of sponge effect when you slowly open your hand to release pressure. Indoor soils that do not fulfill these requirements should be thrown out or amended. See “Soil Amendments” below.