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Choosing the right fertilizer for your lawn or garden

All fertilizers aren't created equal. Here's what you need to know.

October 14, 2009

Fertilizing a lawn in the fall will produce better grass in the spring.

Melanie Maxwell/The Toledo Blade/NEWSCOM/file

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You won't need a dirt doctor to tell you when the soil in your yard is ailing; the vital signs will be obvious. Grass becomes thin and crowded with weeds. Garden vegetables die back. Flowers fade before blooming. Fruit is slow to ripen.

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Probably your planting beds are starved for nutrients — some fertilizer. But what kind and how much? That's when the horticultural equivalent of a physical exam comes into play: a soil test.

"Whether you choose to buy manure or commercial fertilizer is up to you, but a soil test will determine which nutrients are needed," says Steve Heckendorn, manager of the soil-testing lab at Virginia Tech in Blacksburg. "You're not fertilizing the plant. You're fertilizing the soil that feeds the plant. In effect, you're putting food into the plant's refrigerator."

There are hundreds of different soil types in America, each with its own characteristics. A soil test rates them for many things, ranging from texture and water retention ability to their yield potential for specific crops. Nutrient deficiencies are identified along with recommendations for changes.

Used to be, shopping for fertilizer blends was a challenge in chemical code breaking, but the standardized three-digit grade labels now required on bags show at a glance what you need to know.

The first number represents the amount of nitrogen available in the mixture, the second the available phosphate, and the last is potash. If the bag label reads "10-10-10," that means a mixture of 10 percent nitrogen, 10 percent phosphate, and 10 percent potash.

"Nitrogen is associated with color, phosphorous with flowering, and potassium with growth," says Dennis Lukaszewski, urban gardens director for the University of Wisconsin-Extension. "There are other micro-nutrient blends out there for feeding specific plants, but those are the big three."

Here are some fertilizing do's and don'ts:

– Manure has been the fertilizer of choice since the first gardeners turned their first clumps of earth. But be cautious if you have access to the nitrogen-rich farmyard variety.

"Make sure it's fully composted," says Mike Goatley, the extension turfgrass specialist at Virginia Tech. "Fresh manures can burn up plants. Odors can be a problem. It may be something you want to avoid if it's at a stage where it's unattractive to the touch or smell."