Phosphorus Fertilizer in Your Lawn or Garden

“Why are many fertilizer bags labeled ‘phosphorus free’? I thought phosphorus was one of the three important nutrients for plants?” -Madison

You’re right that phosphorus is an important nutrient, but fertilizers containing phosphorus are a major source of groundwater contamination. Did you know that phosphate fertilizers:

• Run off into streams and lakes to create algae blooms that are toxic to humans and kill fish.
• End up in the ocean, where they contribute to oceanic “dead zones.”
• The methods to process rock phosphate cause the release of radioactive waste!

Many states now have regulations limiting fertilizers, detergents, and other products made with phosphates in an attempt to control pollution. That’s why the phosphorus number (the middle number) on your fertilizer bag is usually zero. The exception to this is so-called “starter” fertilizer, which contains higher phosphorus levels specifically to help new seeds to sprout.

If you test the soil in your lawn or garden, you’ll probably find you don’t need to add phosphorus, since most soil contains enough naturally.

I use bone meal and/or compost when planting new shrubs.

There are only two times when I want extra phosphorus for my garden:

• When planting shrubs and trees, especially if I’m transplanting something with lots of broken roots. Phosphorus helps with root growth and establishment of new plants.
• Mixed into the vegetable garden. Phosphorus helps with the production of fruits and vegetables, particularly root crops.

Here are some lawn and garden tips for protecting the environment:

• Use compost! Composted fruits and vegetables provide plenty of natural phosphorus for your garden in a slow-release, organic form.
• Adding organic matter helps the soil release natural phosphorus to your plants, making it (and other nutrients) more absorbable.
• When you need additional phosphorus, use an organic source such as bone meal, soy meal, manure, or bat guano. While rock phosphate is considered an organic source of phosphorus, the radioactive byproducts formed during production can be detrimental to the environment.
• Avoid fertilizers, dish detergents, and laundry detergents that contain phosphate. Manufacturers are catching on, and many products are now clearly labeled phosphate-free.
• Educate your community about the need for reducing fertilizer runoff.

Always choose phosphate-free products.

Further Information

• Use Phosphorus-Free Lawn Fertilizer (EPA)
• Fertilizer and Fertilizer Production Wastes (EPA)