Phosphate Rock

~11.5% to 17.5% total P. Lasts 3 to 5 years. Use up to 9 lbs (22/s qt)/100 sq ft. Very slow releasing.

6. Note: grow biointensive no longer uses many organic fertilizers because of disease, pesticide residue, or heavy metal toxicity challenges.

Soft Phosphate (Colloidal)

~8% total P; ~2% available P. Lasts 2 to 3 years. Use up to 18 lbs (22/s qt)/100 sq ft. Clay base makes it more available to plants than the phosphorus in phosphate rock, though the two are used interchangeably.

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Organic Gardeners Composting

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