Greensand

Greensand is mined from deposits of glauconitic sandstone laid down in ancient marine environments. Its glauconite content carries potassium, iron, and small quantities of other elements bound within a silicate mineral, so the guaranteed potassium analysis is low and varies considerably between sources.

Principal mineral

Glauconite, an iron-potassium silicate

Potassium content

Low and variable, bound within the silicate structure

Other elements

Iron and small amounts of trace elements

Release pattern

Very slow, dependent on gradual mineral weathering

Greensand supplies potassium and iron, but only as the silicate mineral slowly weathers, so the immediate nutrient contribution is small. Its fine, porous structure can also help hold moisture and improve the workability of some soils, which contributes to its reputation as a conditioner.

• Potassium and iron are released slowly as the mineral weathers
• Immediate nutrient availability is low compared with soluble fertilizers
• Physical properties can help soil moisture retention and structure

Greensand is used mainly in organic and horticultural systems, applied to soil as a long-term, slow-release amendment rather than to meet an immediate potassium need. Because release is slow, it is incorporated and allowed to contribute over multiple seasons.

• Used as a long-term amendment and conditioner in organic and garden systems
• Contributes potassium and iron gradually rather than quickly
• Where a prompt potassium response is needed, a soluble source is more effective

Independent evidence for a rapid crop response to greensand is limited, and its low, variable analysis means large quantities would be needed to supply meaningful potassium. It is best regarded as a slow soil-building and conditioning input rather than a nutrient fertilizer with a predictable, near-term effect.