Ecology Blog
Ecomyths

Feeling Fertile?
Myth: All fertilizers are good for plants and for the environment

Myth Explored
When you walk into your local lawn and garden store you’d like to think that they’ve done their homework. The products they’ve put on display will all be perfect for your region, everything will perform as expected and none of it will stir up any environmental mayhem. And what could be more worry-free than fertilizer? You’re just feeding your lawn or garden.

Unfortunately, those folks at the garden center are as busy as you are. They’ve got a business to run, they stock and sell hundreds of different items, and they probably haven't invested the time it takes to research and evaluate every single one. There will be things on the shelves that waste your money, damage the environment and don’t even perform their intended functions.

The Situation
It would be nice if your grass stopped growing when it was exactly two inches tall and dandelions tasted like homegrown tomatoes. But Mother Nature has ideas of her own. Weeds sprout and spread, lawns develop bare patches, and -- though aficionados do exist -- eating dandelions is most definitely an acquired taste.

Fertilizers seem like an easy answer. They’ll make your grass and garden thrive, or at least that what it says on the label. What could be wrong with that?

Plenty, if you’re using the bagged, store-bought stuff. Let’s talk about that.

The Problem
We home gardeners mean no harm when we use fertilizers. We’re merely trying to make our own little corner of the planet bright and beautiful. Unfortunately, most environmental scientists agree that chemical fertilizers create significant environmental problems. A lot of the fertilizer that we put down gets washed into our lakes and streams, where it promotes algae blooms that cover the rocks and shore with algae slime and devour the oxygen supplies needed by the fish. Killing off the fish wreaks havoc with the birds and animals that depend upon them. The area’s ecosystem begins to collapse.

There’s an area in the Gulf of Mexico that demonstrates the problem on a grand scale. The Missouri/Mississippi river system collects agricultural runoff from 31 different states and pours it into the Gulf, where the resulting algae bloom kills or drives away the marine life in an area that can sometimes cover more than 7000 square miles. Called the “dead zone,” it’s a larger version of what happens to our local waterways when we’re careless with our fertilizers.

(Read about the dead zone: http://www.gulfhypoxia.net)

The Solution
“If you feel that you absolutely must use lawn fertilizer, at least be sure to buy a phosphorus-free version,” says Bob Kirschner, Director of Aquatics for the Chicago Botanic Garden. “Our local soils contain all the phosphorus that your lawn really needs. When you buy lawn fertilizer that contains phosphorus, you’re purchasing and distributing an unnecessary pollutant.”

Fertilizers are not all identical, and they’ll list their ingredients on the bag. In many cases the three main ingredients will appear as a row of three highly visible numbers: the percentages, by weight, of nitrogen (N), phosphorus (P) and potash (K). On bags that make these numbers prominent the phosphorus content will be the number in the middle. Look for a fertilizer that lists the phosphorus content as “0”.

Sometimes you’ll have to look for that number in the fine print on the back. That’s especially true when you’re using products that combine things like fertilizer, weed killer and grass seed in a single bag.

Sometimes they’ll make it easy for you by splashing “Phosphorus Free!” across the front of the package. In some places they make it even easier yet -- in Wisconsin and Minnesota they’ve passed laws that essentially ban the sale of lawn fertilizer containing phosphorus. Municipalities like Highland Park, Antioch, Vernon Hills, Lindenhurst, Long Grove, Annapolis and Ann Arbor have done them same. But in most of Illinois we still have to read the bag.

Just remember that you don’t want -- or need -- phosphorus in your lawn fertilizer.

(If you garden with native prairie and woodland plants you’ll want to avoid using any kind of fertilizer at all. Native plants will actually be healthiest in soils with lower nutrient levels.)

There are alternatives to bagged fertilizer. Whether we know it or not, we Americans throw away free lawn fertilizer every season. We bag our leaves and grass clippings, pile them by the curb to be hauled away, and never give it a second thought. It’s pure folly.

Do you want more nitrogen in your lawn? It’s easy -- just leave your grass cuttings on the lawn. The grass you’re cutting still contains the nitrogen that helped it grow. If you keep a sharp edge on your mower’s cutting blade it will chop the grass into small particles that will decompose right back into the lawn. It’s an eco-friendly, slow release nitrogen fertilizer -- and it doesn’t cost a nickel.

And leaves are absolutely magical. Trees sink their roots more deeply than many other plants, and they pull all kinds of nutrients up into the leaf structure. Then -- come autumn -- the trees drop the bounty right into your lap. For lawn fertilizer, let the leaves dry out a bit and then pulverize them with your lawn mower. For a natural mulch and weed control, pile some up. A decomposing leaf is both fertilizer and mulch at the same time.

Any mulch will keep the weeds down and help your garden soils retain water. But when you mulch your garden with a few inches of last year’s leaves you accomplish several things at the same time: You’re making life miserable for the weeds. You’re shielding the soil from the sun and wind and keeping it from drying out as quickly. And the bottom layer of your mulch is slowly and steadily decomposing into compost and high-grade fertilizer; fertilizer that won’t easily run off into the lakes and streams.

What You Can Do
Bag the bag! Let your mower put the nitrogen-rich grass clippings right back into your lawn. And if you keep your grass just a bit taller -- three inches or so -- it will be much healthier. Weeds will have a harder time competing with it and your lawn will need less water.

You can’t beat leaves. They’re natural mulch and natural fertilizer at the same time. And they’re free.

If you must buy lawn fertilizer, only buy phosphorus-free products. Your lawn doesn’t need phosphorus unless you have a brand-new lawn or very unusual soil.

Don’t let applied fertilizer scatter on driveways and sidewalks where the rain will wash it into the storm sewer and off into our lakes and streams.

If you like that “off-the-grid” feeling, buy a push mower. They actually do the job, are great exercise, and they never need a drop of fuel.

Consider avoiding the use of chemical fertilizers altogether. Better yet, plant a prairie in your front yard and avoid both fertilizing and lawn mowing!

Next Month: Mulches
Teaser: Never purchase cypress mulch. Cypress mulch is no longer made with mature trees that have developed the natural resistance to rot that once made cypress so popular. Instead, it’s made with immature trees that lack that resistance. These days, buying cypress mulch does nothing but contribute to the demise of our ecologically important cypress groves.

Resources
Duluth Streams.org: Lawn Fertilizer Doesn't Just Fertilize Lawns http://www.duluthstreams.org/understanding
/impact_fertilizer.html

Louisiana Universities Marine Consortium: Learn about the dead zone in the Gulf of Mexico: http://www.gulfhypoxia.net/

National Wildlife Federation: What’s wrong with using cypress mulch?
http://www.nwf.org/News-and-Magazines/National-Wildlife/Gardening/Archives/2006/Cypress-Distress.aspx

University of California: What’s so great about grass clippings?
http://cecalaveras.ucdavis.edu/grass.htm

Texas A&M University: Why save your leaves?
http://aggie-horticulture.tamu.edu/extension/
homelandscape/dontbag/dontbag.html

University of Illinois: Spring Lawn Care Guide http://web.extension.illinois.edu/regions/
lawnandgarden/SpringLawnCareGuide05.pdf
 


 


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