Phosphorus Not Dangerous If Used Right Says LSU AgCenter Horticulturist

Thomas J. Koske  |  7/2/2005 2:04:43 AM

News You Can Use For July 2005

Phosphorus (P) is an essential nutrient for plants and soils, but is often eyed as an element of concern. High levels can spark algae blooms in waterways and decrease water quality, according to LSU AgCenter horticulturist Dr. Tom Koske.

Phosphorus need not be a threat if best management practices are followed. For example, never dispose of lawn clippings or plant materials in storm drains or on drainage banks where nutrients can wash into surface waters.

Also, avoid spreading fertilizer on impermeable surfaces like walks and drives. If they receive some granules, sweep or blow them back into the lawn.

Koske says to avoid spreading fertilizers, or most chemicals for that matter, near ponds, bayous or drainage ditches. Leave these areas as buffer strips to catch and process nutrient amendments.

"You didn't want to mow much right up next to the waterway anyhow, so don't promote that growth," the horticulturist advises, adding, "Be sure your mower discharges clippings back into the lawn and not into the street or waterway."

Test the soil every several years to see if available soil P is too low. You still deserve good plant growth. It's just that most mature plants are very content with moderate soil P levels.

Some P fertilizer is needed to maintain medium soil P levels. Replenish the soil with at least 1/2 pound P fertilizer per 1,000 square feet once per season if clippings are returned and twice per season if clippings are bagged. Fertilizer P is listed as % P2O5 by weight, so if you need a pound of P2O5 from a 0-6-0 analysis, you spread 16.7 pound of the fertilizer.

Phosphorus is very important for seedling growth and spring reestablishment of warm-season lawns. Apply l pound P2O5 per 1,000 square feet at establishment or sodding on fertile soils unless a soil test advises more. Always start the spring green-up season with a complete (containing all three numbers) fertilizer. This is usually mid- to late March or April depending on your area of Louisiana.

"Following BMPs for P fertilization should yield adequate growth, color and pest resistance without harmful pressures on our water’s quality," Koske says.

For related topics, click on the Lawn and Garden link at the LSU AgCenter Web site,


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Source: Tom Koske (225) 578-2222, or

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