One of the oldest and most reliable soil-building amendments in organic gardening. Greensand is glauconite — an ancient marine mineral formed from the compressed shells and sediment of sea creatures millions of years ago. It contains potassium, iron, silica, and over 30 trace minerals in a slow-release form that feeds soil biology and builds long-term mineral wealth in the ground.
 
The defining characteristic of greensand is patience. It releases nutrients slowly — over years, not weeks — through the action of soil acids, moisture, and microbial activity. That makes it the wrong choice for a quick mid-season potassium fix, but exactly the right choice for gardeners building a raised bed or planting perennials where a deep mineral foundation will pay dividends for years. Apply it once and it keeps working long after faster amendments have been exhausted.
 
Best applications:
Raised bed establishment — work into the top 6–8 inches when building or refreshing a bed
Perennial plantings — blueberries, fruit trees, asparagus, native meadow plantings, and any crop staying in the ground for multiple seasons
Long-term container plantings — fruit trees and shrubs in large fabric bags where the mix will persist for several years
Paired with compost and worm castings to create a fully mineralized, biologically active bed
 
Not the best choice for:
Grow bags with annual crop rotations — the growing season is too short and container biology too limited for meaningful release
Mid-season potassium correction for fruiting crops — use soluble kelp extract powder for fast-acting potassium when tomatoes, peppers, or squash need support during fruit set
 
Application rate:
New raised bed: 2–4 lbs per 100 square feet, worked into the top 6–8 inches
Established bed top-dress: 1–2 lbs per 100 square feet annually
Container perennials (20-gallon+): 2–3 tablespoons per bag at planting
 
Greensand does not expire or lose potency — it is a mineral, not an organic compound, and is as stable as the rock it came from. A bag stored for years is identical in value to a fresh one.
 
OMRI listed for certified organic production.