Is nitrogen always bad?

When -- and when not -- to fertilize the lawn

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📬 Ask Jessica

DEAR JESSICA: What is wrong with weeds? You keep recommending nitrogen while our waters are suffocating because of the overuse of fertilizer. Is a green lawn more important to you than the health of our water and the animals who depend on it? —Ed Bickard

DEAR ED: Absolutely not.

But amending the soil with nitrogen fertilizer isn't problematic when it's warranted; nitrogen is a soil nutrient that's vital to all plant life. When it’s deficient, plants simply won’t thrive.

Problems arise, however, when nitrogen is applied at higher rates than needed, or too often, or at the wrong time of year, when it simply cannot be taken up by plants, or in addition to other nitrogen-adding amendments, like manure. When over-applied, you are correct: excess nitrogen that isn't utilized by plants ends up polluting the groundwater and fertilizing the wrong plants (weeds, invasive species, etc.) at the water table, which leads them to outcompete native plants that are an important part of the ecosystem and food chain.

The effect on the food chain can be devastating, as insects and wildlife that depend on those native plants for food are starved, as are their predators. At the water table, we see die-off of fish and other aquatic organisms due to excess nitrogen, as well as algae overgrowth and contamination of our drinking water, which has been shown to cause significant health problems, particularly in infants (blue baby syndrome) and the elderly.

The decline of our native insects (including, but not limited to pollinators) already has become problematic. Without insects, there would be no flowering plants, and the loss of flowers would lead to the collapse of the food chain that supports wildlife. The biosphere – the part of the Earth that supports life – would rot because insects help decompose the soil as they work through it and enrich it with carbon, which builds topsoil and prevents flooding.

These are all reasons to rethink the lawn — or at least rethink the need for a perfect lawn. This means avoiding the automatic application of fertilizer based on timing, but it doesn’t necessarily mean avoiding nitrogen altogether.

Keep in mind that grass can only utilize fertilizer when it’s actively growing, and most turfgrass is dormant when the temperature is below 55 degrees as well as at the height of summer’s heat. So, in New York, for example, applying nitrogen in early spring, in mid-summer, or in fall would serve little purpose aside from feeding the devastating process mentioned above.

In fact, it’s illegal in New York State to apply nitrogen between Dec. 1 and April 1. In Nassau County, the restriction is tighter —no nitrogen applications are permitted between Nov. 15 and April 1, and in Suffolk County, the off-limits window is from Nov. 1 to April 1. (Check with your local municipality for restrictions in your state or county.)

Safer ways to give the lawn the nitrogen it needs include removing bags from mulching mowers and allowing grass clippings to remain on the lawn. As they decompose, they’ll add a natural (and free!) source of nitrogen to the soil. If you don’t have a mulching mower, simply mow over clippings to shred them and apply to the lawn (don’t apply fresh clipping to beds and borders, though, because the nitrogen they contain will burn plants.)

Amendments like well-rotted manure also are great sources of natural nitrogen.

Incorporating nitrogen-fixing plants like clover into the lawn would replace the need for synthetic fertilizers, as well. Hear me out: Clover was actually considered a desirable component of commercial turf seed blends in the mid-20th century. But when chemical weed-control products came along to kill crabgrass, the bane of suburbia, in the 1950s, clover became collateral damage. And then, in the quest for what became the new standard of a “perfect” lawn, Americans became obsessed with eradicating clover.

Clover naturally adds nitrogen — the active ingredient in lawn fertilizers — to soil. It’s common practice to plant it as a cover crop on farms to nourish the soil between seasons. And when it pops up naturally in your lawn, that’s a clear indication that your soil is either low in nitrogen or isn’t getting enough water. As clover dies, including whenever an infiltrated lawn is mowed, its roots release nitrogen into the soil. This, of course, is preferable to applying synthetic fertilizers.

And if your soil is deficient and you aren’t willing to plant clover and can’t apply manure or allow clippings to enrich the soil, a light application of fertilizer once (or twice, at most) a year is OK. Just follow package directions — and remember that less is more.

This brings us to your question: Why did I recommend adding nitrogen to lawns in order to eradicate certain weeds when nitrogen is a pollutant? Because nitrogen is a necessary nutrient and it’s only a pollutant when it’s used improperly, excessively or at the incorrect time. When it’s deficient, nature gives us clues, like allowing certain weeds to take hold.

For those seeking to address those weeds, I’d much rather recommend correcting a nutrient deficiency than suggest the application of chemical weed killers.

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👏 Sunday shoutout

“My azaleas always put on a beautiful show for Mother’s Day!” says Rita Stasi of Miller Place, NY.

Enjoy them, Rita! And thanks for sharing!

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📧 Send me your feedback!

I welcome your comments and suggestions, so please send them along — as well as any topics you’d like to see covered and questions you’d like answered in the Ask Jessica section.

Until next week, stay safe. Be well. And always keep your mind in the dirt. —Jessica


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