So you broadcast those fertilizer granules from the bag as directed. What happens next?
How your lawn reacts depends on a lot of factors, including the air and soil temperature, how damp the soil is, what kind and how many microbes you have in your soil, and especially the type of fertilizer you use in the first place.
All of these add up to reasons why it’s important to pick the right fertilizer for the right situation and apply it at the right time in the right way.
That all-important ingredient: nitrogen
Vitalii Petrushenko / iStock / via Getty Images
By far, the most important nutrient that a lawn needs regularly to maximize growth is nitrogen. This element determines your lawn’s growth rate, density, and color.
In traditional fertilizers, nitrogen comes from compounds containing ammonium, nitrate, and especially urea. These dissolve readily in water, so once wet, they quickly break down into ammonium nitrate – the form of nitrogen that grass plants take up and use.
The advantage of these “quick-release” nitrogen sources is that they’re fast to “green-up” a lawn and are relatively inexpensive to produce.
The downsides are that they can burn a lawn when spilled or over-applied, they generally break down completely within about eight weeks, and they’re prone to losing nitrogen into the air and through leaching when rain carries the dissolved runoff into streams.
The slow-release approach
To address the above downsides, fertilizer companies have developed so-called “slow-release” and “controlled-release” fertilizers that 1.) virtually eliminate the chance of burning a lawn, 2.) spread out the working window from eight weeks to 12 or more weeks, and 3.) reduce the levels of nitrogen running off and potentially polluting the water.
One way to do that is by coating the nitrogen compounds, usually with sulfur or a polymer. Soil microbes and moisture gradually erode or work their way through these membranes in order to release the nitrogen inside, resulting in a longer and more gradual feeding time than uncoated quick-release nitrogen sources.
Warmer temperatures and damp soil speed up the release rates. Cool, dry conditions slow them down, especially for sulfur-coated products, which are more dependent on soil moisture and microbial activity than polymer-coated products.
This is why it’s a good idea to apply granular fertilizers just before a rain – or to water them in soon after applying.
Nitrogen release rates also are affected by how well each granule is coated and how much cracking or breaking has occurred after manufacture.
Although coated fertilizers hardly ever burn, they occasionally produce some spottiness in lawns when there’s enough variability in the breakdown factors.
The methylene urea approach
The second main slow-release technology is using a nitrogen source called methylene urea, which is made by combining urea with an organic aldehyde compound (most often formaldehyde). Soil microbes gradually break down methylene urea at a predictable rate that’s also influenced by temperature and soil moisture (i.e. faster release when it’s hotter and wetter).
One advantage of this approach is that it retains its slow-release rate even if the granules are cracked, chipped, or crushed.
Another plus is that methylene urea’s breakdown rate varies in concert with a lawn’s need for nitrogen. In other words, the release rate naturally slows in cooler weather when grass-growth needs are less and speeds up when the weather warms and grass-growth rates increase.
GreenView’s Fairway Formula Lawn Fertilizers derive about three-fifths of their nitrogen from methylene urea with the remaining amounts coming from quick-release urea sources.
The result is a product that both quickly greens up lawns (from the straight-urea component) but is also slow to burn and effective for 12 weeks per application (from the methylene urea component).
That means lawn-owners can fertilize just twice a year instead of four times, using Fairway Formula 27-0-5 Lawn Fertilizer in mid-spring and Fairway Formula 30-0-12 Fall Fertilizer in early fall.
The fall version contains slightly more potassium and slightly less sulfur than the spring version.
Potassium is usually supplied in the form of muriate of potash or sulfate of potash, and like slow-release nitrogen compounds, breaks down gradually in the soil. It plays a key role in a lawn’s drought tolerance, cold-hardiness, and disease resistance.
Sulfur aids good growth and color and shows up as yellowing blades when deficient.
A third option...
Organic fertilizers that come from by-products of plant and animal processing offer a third approach to slowing down and spreading out a lawn’s nitrogen use.
These fertilizers break down gradually and naturally over time, but their nutrient rates are relatively low – typically a third or less than the nutrient rates of the above coated and methylene-urea products.
For those leaning organic, GreenView offers a blend of natural organics (feather meal, soy protein, and meat and bone meal) with methylene urea for a product that boosts nutrient levels while avoiding burns, limiting runoff concerns, and lengthening the release time of nitrogen.
Turf Nurture Natural Base Lawn Fertilizer has a nutrition breakdown of 15-0-7 and can be applied spring, summer, or fall whenever the lawn isn’t frozen or dormant.