Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

Do you have additional gardening questions? Please contact us. Here's how.

Horticulture Questions and Answers

When and how do I fertilize my cool-season lawn?

Providing proper nutrition is one of the most important maintenance practices that you can do to keep your cool-season lawn healthy and attractive.

Proper fertilization provides the nutrients needed to enable grasses to survive the stresses they may incur from mowing, weeds, insects, diseases, and drought. Most importantly, it also provides that nice green color we love to see.

Improper fertilization, however, can do harm to the lawn and the environment. Too little fertilizer often results in a yellowish green, thin stand of grasses that have limited ability to recover from the stresses above.

Over fertilization of cool-season grasses, especially with quickly available (water soluble) nitrogen particularly in the spring of the year overly stimulates top growth and increases the need for mowing. Additionally, it has the potential to “burn” the roots and foliage of the grass plant, often leaving brown or dead spots in your lawn.

Over fertilization may also lead to lower drought tolerance, greater susceptibility to various leaf diseases, insect activity, and leaching of excess nutrients into the groundwater.

To avoid over fertilizing, start your lawn fertility program with a soil test. It will provide the baseline information you need to do a proper job of fertilizing. It not only tells you the soil's pH, but also the levels of phosphorous, potassium, and organic matter in the soil. See “How do I test my soil?”

Established cool-season lawns need a higher percentage of nitrogen and very little additional phosphorous and potassium.

All bags of lawn fertilizer contain a set of three numbers that represent the percentage of primary nutrients (by weight) in each bag. The first number represents nitrogen (N), the second phosphorous (P), and the third potassium (K). Additionally, the back of the bag lists whether the available nitrogen is slow release (water insoluble), quick release (water soluble) or a combination of the two.

The majority of synthetic lawn fertilizers contain a combination of the two types. Slow release types of nitrogen in these products include isobutylidene diurea (IBDU), sulfur-coated urea, and urea formaldehyde (a.k.a., urea form).  Quick release types include ammonium nitrate, ammonium sulfate and urea.

Organic lawn fertilizers that are formulated from sewage sludge (such as Milorganite), composted manures, soybean meal, and other natural materials are excellent sources of slow release nitrogen.

Try to choose a lawn fertilizer with a good percentage of slow release nitrogen. The nitrogen in these formulations is released over an extended period of time. This provides more uniform growth, grass color, and reduces the pitfalls of over fertilization.

So when should I apply it and how much should I use?

Turfgrasses should be fertilized in their most active periods of growth. For cool-season grasses such as turf type fescues, Kentucky bluegrasses, fine leaf fescues, and mixes/blends of the above, fall and spring represent these periods of active growth with fall being the most desirable time of application.

Fall applications of nitrogen provide good turf color and density without excessive shoot growth. Nitrogen applied in the fall promotes strong root growth that continues until the ground freezes. Cool-season grasses with strong roots recover better from drought stress. Some nutrients from fall applications are stored in the root system and provide early spring green-up without excessive shoot growth.

Cool-season grasses require about 2 ½ - 3 pounds of actual nitrogen per one thousand square feet per year. Calculate the amount of actual nitrogen in a bag by first multiplying the percentage of N (the first number) by the total pounds of product in the bag. As an example, a 45 pound bag of a 30-0-4 would contain 13 ½ pounds of actual nitrogen. This product, applied at the recommend rate on the bag of 3 lbs per 1,000 square feet, results in a little less than 1 pound of actual N per 1,000 square. It’s best to apply no more than 1 pound of actual nitrogen per thousand square feet in one application, especially if the nitrogen is all in the quick release (water soluble) formulation.

For cool season grasses, apply the majority of the recommended amount of fertilizer in the fall. Dividing the total amount needed into 3 equal applications is a good practice. One method is to make all of the applications in the fall and apply 1/3 of the amount in September, October, and November.

Another method is to apply 1/3 in September, November and mid May. If this method is used, the application in May is best done with an organic slow release fertilizer.

If crabgrass control in the spring of the year is needed or desired, it’s best to apply a product without fertilizer.  See "Turf Crabgrass Control."

Finally, if you want to reduce the amount of fertilizer you need to apply to your lawn by 25%, practice “grasscycling”. See our FAQ on "Should I Collect My Grass Clippings?"