Just as the human body requires vitamins and minerals to function properly, grass needs about 16 known nutrients for growth and survival.  However, lawns need higher amounts of certain nutrients than what are naturally present in the soil.  This raises three commonly asked questions about fertilizing:
1. What type of fertilizer should I use?
2. When should I fertilize my lawn?
3. How do I apply fertilizer?

The Right Food for Healthy Grass

Nitrogen (N) is, by far, the most abundant element found in plants and also the one most supplemented.  Phosphorous (P) is second, followed by potassium (K).  Each is critical for plant growth, development and recovery from injury.  Excessive or deficient amounts of these nutrients can lead to unwanted problems, so proper timing, amount and application techniques are critical.

Vast differences in climate, soil type and grass species make it impossible for a single fertilizer program to cover all types of lawns.  However, a few generalities can be made surrounding these questions. (For a more comprehensive guide, check the "Grasses" section on yarddoctor.com.)

Nitrogen comes in two forms:  Soluble in water (quickly available to the plant, or "fast release") and insoluble in water (slowly available to the plant, or "slow release").  A heavy dose of soluble fertilizer can sometimes cause unwanted growth spurts and burn the yard.  Conversely, if only slow release nitrogen is used, the yard may respond more slowly during favorable growing conditions and unpredictably during times when the lawn is subject to stress.

Therefore, the ideal solution is usually a combination of fast and slow release nitrogen.  This is the idea behind most high quality lawn fertilizers – meet the daily needs of the plant for an extended time frame (generally six to 12 weeks).  Fertilizer labels typically outline a guaranteed analysis and break down the types of nitrogen the product contains.  The fertilizer is highly suspect if this information is not present.  Also note that slow release nitrogen products are more expensive than their quick release counterparts.

Optimal Fertilizing Time

Simply stated, fertilize when the lawn is actively growing; leave it alone when it is not.  Fertilizer cannot make a lawn grow when environmental conditions (temperature, water, light) aren't right.  The active growth times for cool season grasses are when temperatures are between 60 degrees and 80 degrees.  For northern climates, this usually means the most growth occurs in spring and fall with growth slowing in prolonged hot temperatures.  Meanwhile, warm season grasses grow best when temperatures are above 80 degrees.  Therefore, apply fertilizer during active growth times to build roots and strengthen the plants so they can survive periods when growth is not as active and there is greater potential for stress.

Those who live in the Northern U.S. with cool season grasses can employ the "holiday calendar" fertilizing schedule.  As the name implies, the applications center around four U.S. holidays:  Memorial Day, Fourth of July, Labor Day and Thanksgiving.  These dates can be adjusted based on different geographical regions and climates.  Consult the Yard Doctor Web site's "Yard Care Calendar" for specific schedules.

Applying Fertilizer Like a Pro

Fertilizer does not lie about where it has been applied.  Those dark green streaks (that may turn to an ugly brown) are a dead giveaway if a mistake has been made.  The goal of any fertilizer application is to put down the amount you want, where you want it.

The three most common application methods are liquid sprayer (usually out of a garden hose), drop spreader, and rotary, or broadcast, spreader.  While a liquid sprayer is quick to use, it is challenging to achieve an even application.  A drop spreader makes it easy to set the application rate, but the whole yard will need to be covered, just like a mower.  The rotary spreader is by far the most efficient and accurate device for fertilizer applications because it quickly distributes the fertilizer to a broad area.

Following label directions is very important when considering how much fertilizer to use.  As a general rule, apply up to one pound of soluble nitrogen per 1,000 square feet.  (Fertilizer products aren't pure nitrogen, so the actual application of product may be several pounds.)  Because insoluble fertilizer products have less potential to burn the lawn, up to 2 pounds per 1,000 square feet may be applied.

For Best Results, Follow These Tips:

1. Buy a quality spreader.  Inexpensive ones will break down while a good quality spreader will last a lifetime if cared for properly.
2. Always wash the spreader after use.  Because of its salt properties, most fertilizer is very corrosive.
3. Apply fertilizer during ideal conditions.  The best conditions combine freshly mowed grass, no wind and light dew still on the ground.  This will keep the spreader accurate over a smooth ground with its tracks visible.
4. Know the spreader's capabilities.  Most rotary spreaders cover a swatch 6 to 8 feet wide.  Keep the wheel tracks at least that far apart on every pass for best results.  For added confidence, set surveyor flags at the ends of your yard, 8 feet apart, to provide reference points for an even application.
5. Avoid skips in the fertilizer by cutting the amount in half and traveling in two directions.  This trick, used by the pros, is the biggest reason why you don't see streaks caused by too much fertilizer at golf courses and baseball diamonds.
6. Start walking before turning on the spreader and shut it off before you stop walking.  This trick will prevent over-applications.  Keep the spreader off when turning around.  Instead, make one pass around the perimeter of the yard to even out the application.
7. Use the spreader setting guidelines on the fertilizer label.  Remember that there will be variations among various models of spreaders.
8. Avoid using products with large particles in rotary spreaders.  Products with larger particles are better suited for drop spreaders.  Sufficiently applying fertilizer with a drop spreader requires overlapping each pass by at least the width of the wheels.
9. Water the lawn.  Improve the fertilizer's efficiency by watering the lawn soon after an application.  Better yet, try applying fertilizer just before it rains.

Finally, it's easy to be environmentally conscious when using fertilizer.  Try these tips:
• Leave your grass clippings on the lawn.  This simple gesture saves 1 to 2 pounds of nitrogen per year.
• Consider adding a liquid fertilizer application to lawn irrigation systems.
• Keep fertilizer out of waterways.  Use a drop spreader for accuracy around sensitive areas.
• Clean up spills and sweep up driveways and walks to prevent runoff.

Trey Rogers, Ph.D.
Briggs & Stratton Yard Doctor

For more of The Yard Doctor read previous installments of this column in our magazine archives.

The Yard Doctor - Trey Rodgers, Ph.D

Profile of The Yard Doctor Dr. Rogers’ interest in lawn care began early, while he was working as a golf course groundskeeper during his teens in his hometown of Fort Smith, Ark. He earned the nicknames “Sultan of Sod” and “God of Grass,”...

See The Yard Doctor website for more tips from Trey Rodgers, Ph.D.

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Lawn Care Tips by The Yard Doctor

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