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No, phosphorus doesn't stimulate root growth

By Robert Cox, Colorado State University Cooperative Extension agent, horticulture

No matter how often you've been told that phosphorus and phosphate fertilizers, stimulate root growth, don't believe it.

Many of us think phosphorus promotes root growth because we're taught to place phosphates in the root zone, below the soil surface where the roots are growing. There's a reason for putting the phosphate there: If we sprinkle phosphates on the soil surface, they don't leach into the soil and they can't be absorbed by the roots.

So, because we're taught to apply phosphates in the root zone, we've concluded they promote root growth. They don't -- not any more than does zinc, magnesium, nitrogen or potassium.

When you start a new lawn, landscape, vegetable or flower garden, prepare the soil well by rototilling in organic materials and phosphate fertilizers. Superphosphate and treble phosphate are much more effective under local soils than is bone meal (calcium phosphate).

Photo: Judy Sedbrook

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Date last revised: 01/05/2010