Cation exchange capacity (CEC) is a measure of how well a soil or growing medium can hold and exchange positively charged nutrient ions, called cations. Important plant nutrients affected by CEC include potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), and ammonium (NH₄⁺). Materials with higher CEC can retain more nutrients in the root zone instead of allowing them to leach out during watering.
CEC is influenced by the amount and type of clay and organic matter present in a substrate. Compost, peat moss, coco coir, and humus generally contribute to higher CEC, while coarse sand, perlite, and bark-based materials tend to have lower CEC. In container growing, CEC affects how frequently nutrients must be replenished and how stable nutrient availability remains between waterings.
A growing medium with very low CEC may dry and drain quickly but require more frequent fertilization because nutrients are not retained effectively. Extremely high CEC can hold nutrients strongly, sometimes slowing their availability to plants depending on pH and moisture conditions. CEC is usually expressed in milliequivalents per 100 grams (meq/100g) of substrate.
See Also
