What Does Phosphate Do for Grass?

Starter Fertilizers

• Phosphates play an important part in the early development of the grass plant. Starter fertilizers--which are applied when a lawn is started or planted--have higher levels of phosphates than other lawn fertilizers. But phosphorus is generally the least abundant item in the normal nitrogen-phosphorus-potassium fertilizer mix. Phosphates are necessary for the photosynthesis process in which plants convert carbon dioxide and light into sugars and oxygen.

Root Development

• Grass and other plants seek phosphates in the soil. If the level in the soil is too low the roots expand their surface area to seek phosphates. This can lead to grass plants overdeveloping their roots, at the expense of the above-ground portion of the plant.

Grass Clippings

• Phosphorus that's absorbed by the plant ends up in the grass leaves and stems. Each time the grass is cut the phosphates stored in the leaves are lost to the plant. This can amount to as much as a third of a pound per 1,000 sq. ft. in each growing season if the lawn clippings are removed from the yard. These phosphates must be returned to the lawn through fertilization each season.

Runoff

• Naturally occurring phosphate or applied fertilizer phosphate sometimes is washed from the lawn into streams or ponds. High phosphate levels in water leads to excessive growth of algae and other aquatic plants. This can damage the water for fishing or recreational uses. Homeowners should prevent grass clippings from decaying on streets or in storm sewers. The decay of the clippings releases the phosphates, which wash through the sewer system into streams or lakes in most communities.