Sorry, this item cannot be posted to a PO box address. Suitable for organic gardens. The high CEC makes zeolite particularly valuable in holding and slow releasing valuable nutrients to plants, mainly ammonium nitrogen (NH4+), potassium (K+) and magnesium (Mg+), calcium (Ca+) and trace elements. Zeolites are complex hydrated alumino silicates, which can occur as a natural mineral or may be synthesised artificially. There are over 40 species of natural zeolites. Zeolites have very open frameworks characterised by networks of channels or pores. This gives the mineral a very large surface area. The structure has a net negative charge and with its large surface area has a high cation exchange capacity (CEC). This high CEC enables zeolite to absorb and freely exchange positively charged cations, such as Ammonium Nitrogen and Potassium. The addition of zeolite into potting mixes regulates the uptake of nutrients by absorbing excess nutrient from growing mix and storing it within the structure of zeolite. When the particular nutrient becomes deficient in the solution around the root zone, it is released from the zeolite and made available to the plant. This greatly reduces leaching of excess nutrient and ensures more efficient use of applied fertiliser. In general plant health and colour are improved with the use of zeolite and the life of applied nutrients in the mix is extended. Zeolite is best applied when preparing gardens so that it can be incorporated into the soil.