Lawn Fertilization - A Brief Overview

Nitrogen

To maintain a healthy lawn, nitrogen fertilizer is essential¹. Conventional turfgrass management tells us that the optimal amount of nitrogen to apply is 4 pounds² of nitrogen (per 1,000 square feet). Do not bag and remove grass clippings³, as clippings return key nutrients to the soil, including nitrogren at a rate of about 1 pound per year. Thus, I apply 3 pounds of nitrogen over our 6 months of turfgrass growth in Wisconsin.

The science

Soil organisms quickly convert urea to nitrate, which the turfgrass can use. The urea applied is only available for about 4 weeks, during which the nitrogen is taken up by the plant. Excess nitrate can leach through the soil profile and end up in groundwater.

Other pitfalls of over-applied nitrogen include: diminished root growth, weakening the plant's ability to survive summer drought and heat; susceptibility to disease; and a surge of top growth, increasing mowing requirements.

Benefits of this approach

The coated urea granules release the fertilizer slowly over 6-8 weeks. This approach decreases the number of applications required, saving you money. The slow release of nitrogen from these coated granules minimizes losses to the environment, such as leaching or volatilization. Your lawn will love it, too, because the nitrogen is reliably available between the 4 applications.

Other nutrients

There's no way to get around nitrogen input requirements. Additionally, most lawn care includes the application of potassium⁴. Other nutrients, however, are usually present at sufficient levels. A soil test can reveal whether or not your soil has any nutrient deficiencies. Contact me to get your soil tested, and I will also give you an expert interpretation of the results⁵.

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Notes

1. Some soils are very high in organic matter, supplying enough nitrogen to turfgrass via mineralization. However, without fertilizer inputs, this pool of organic nitrogen will be depleted over time.
2. I don't entirely agree with the 4 pounds of nitrogen approach for home lawn care. The 4 pounds figure was determined based on maximizing corn yield (also a grass). However, it's usually not a homeowner's goal to maximize grass clippings and mow the lawn like crazy. As a pro, I know that people generally don't want to pay to have their lawn mowed 10 times a month, and weekly mowing is the closest approximation I can offer.
3. Let your grass clippings decompose back into the soil. Contrary to popular belief, grass clippings do not contribute to thatch, as the leaf tissue decomposes quickly. If you find that your mowing is leaving an unsightly amount of grass clippings, mow more often or raise the deck for a higher cut. Bag clippings as a last resort.
4. Potassium is most commonly included in "winterizer" fertilizer products. Despite the marketing you'll see, the timing of potassium application is not critical; instead, maintain a sufficient level of potassium in the soil at all times. I apply 1 pound of K₂O (potassium) in the form of potash.
5. Interpretation of soil test results is a fine art - considering the extractant used, understanding the competing methodologies, etc. I appreciate the companies that offer mail-in soil test kits, and following their recommendations can yield fine results for your lawn. However, these business models are biased toward selling products. Whereas their recommendations are not incorrect, you will probably be applying more product (and spending more money) than is necessary to achieve those results. I offer soil tests for a nominal fee, providing correct interpretation without recommending unnecessary inputs.