What is Winter Fertilizer?

One woman farmer is fertilizing the lawn soil. Fertilizer For Lawns in springtime for the perfect lawn.

A winter fertilizer is a lawn fertilizer applied in mid-to-late fall to prepare the turf for winter (winterize the lawn). It keeps the grass green for longer, improves its resistance to winter kill, and supports a faster and healthier green-up in the spring.

The NPK ratio of winter fertilizers

Synthetic fertilizers have three numbers separated by dashes on their bag labels. They are the N-P-K ratio and tell you how many parts of nitrogen, phosphorus, and potassium are in the product. For example, 21-0-20  means 21 parts nitrogen, 0 phosphorus, and 20 parts potassium.

Here’s what each of these important turf nutrients offers your grass when applied in the fall:

  • A small amount of nitrogen (N) applied in late fall keeps cool-season grasses green for longer, allows the plants to build nutrient reserves, speeds up greening in the spring, and helps the grass develop healthier roots.
  • Potassium (K) is essential when winterizing a lawn. When provided in the fall to correct a deficit, it strengthens the cell walls, improves nutrient and water absorption, and reduces water loss. It increases cold hardiness and drought resistance, reducing the risk of winter kill.
  • Phosphorus (P) supports root development and general growth. It’s also a significant water pollutant. Use a fertilizer with phosphorus only if a soil test shows deficiency.

Best winter fertilizer NPK for cool-season grasses 

Fertilizer in soil. The concept of plant care is the need for feeding with various fertilizers. Text N, P, K, Ca, Mg, S, Mn, Cl, B, Fe, Zn
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John Fech, an Extension Educator for the University of Nebraska–Lincoln, says a good winter fertilizer for cool-season grasses should have a 1-0-1 or 1-0-0.5 ratio. This means looking for a product with equal amounts of nitrogen and potassium or up to two times more nitrogen (e.g., 21-0-20 or 19-2-13). 

Too much potassium in the grass leaf can sometimes increase the risk of snow mold and diseases, so be mindful when choosing the right winter fertilizer for your lawn.

The best way to choose a winter fertilizer: 

  • Check the lawn for signs of potassium deficiency (older leaves turn yellow then brown around the margins; visible on the entire lawn)
  • If you see any, take a soil sample and send it to the local Extension Office for a soil test.

The test will return with recommendations on how much potassium to apply, and you can use them to choose a proper winter fertilizer. 

The easy way to choose winter fertilizer (if not willing to do a soil test): Travis Shaddox,  assistant professor at the University of Kentucky, advises using a 2:1 fertilizer (two times more nitrogen than potassium) if you’re unsure your turfgrass has a potassium deficiency. This way, you add some potassium to treat an eventual deficit but not so much as to harm it. 

Best winter fertilizer NPK for warm-season grasses

feeding lawn with granular fertilizer for perfect green grass
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“Summer-type fertilizers or winterizers containing nitrogen are not recommended for southern lawns,” says Keith Collins, county agent for the LSU College of Agriculture. He explains that stimulating fall growth with nitrogen can increase brown patch disease and winter kill.

“The only fertilizer that should be applied in the fall is potash. Muriate of potash, 0-0-60, may be applied in September or October to provide increased cold tolerance. Apply at a rate of 1-2 pounds per 1,000 square feet. For extra color on fall turf, apply a foliar iron spray. This will help extend greenness into fall,” Collins says.

Further south, in Florida, nitrogen applications are banned from June 1 to Sept. 30. To feed the hungry lawn and prepare it for winter, some nitrogen may be added in the fall. Larry Williams, an extension agent for the University of Florida, recommends winter fertilizer with an NPK of 9-2-24, 5-2-14, 8-2-34, or 5-0-22. 

The above products have roughly a 1:2.5 to 1:4.5 ratio, with much less nitrogen than recommended for cool-season grasses and a lower risk of triggering late growth for summer grasses.

The type of nitrogen in winter fertilizers

In an interview for Turfgrass Epistemology, Dr. Eric Miltner, agronomist with the Koch Turf & Ornamentals, advises using a quick-release water-soluble fertilizer if applying a small amount, up to 0.5 lbs. of nitrogen per 1,000 square feet. 

For late fall applications at a higher rate, Dr. Miltner recommends using a fertilizer that also includes some slow-release nitrogen, such as polymer-coated urea (PCU), to prevent off-site mobility and leaching into the water table. 

Soluble nitrogen feeds the grass until dormancy, while slow-release nitrogen shuts down during winter and stays in the soil until the spring greens up to provide food for new growth.

FAQ about winter fertilizer

What’s the difference between fall fertilizer and winter fertilizer?

The main differences between a fall fertilizer and a winter fertilizer are the time of application and the nitrogen content. Fall fertilizers are slow-release and are typically applied in early fall while the grass is actively growing. Winter fertilizers are mainly quick-release and are applied in late fall when the grass is close to dormancy.

What are the main benefits of a winter fertilizer?

The main benefits of a winter fertilizer are:

  • Better fall and winter color
  • Richer nutrient reserves for winter and spring
  • More robust root, stolon, and rhizome growth in fall, winter, and spring
  • Improved cold hardiness, disease resistance, and drought tolerance 
  • Earlier green-up in the spring with denser shoots. 

When is the best time to apply winter fertilizer?

The best time to apply a winter fertilizer is after the last mow of the season. It’s when the grass is still green and biologically active (making photosynthesis) but stops growing leaves and shoots and focuses on roots and nutrient reserves.

Get it right! Call the pros to winterize your lawn

Winter fertilizer applications can help your lawn green up faster and healthier in the spring, but can also break your turf if you choose the wrong product. Play it safe! Hire an experienced lawn care pro with Lawn Love to winterize your turf, sit tight, and enjoy the lush, green results. 

There’s more to winterizing a lawn than the right fertilizer. Lawn Love pros can also handle the last mow of the season, leaf removal, yard cleanup, and lawn aeration

Sources:

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Sinziana Spiridon

Sinziana Spiridon is an outdoorsy blog writer with a green thumb and a passion for organic gardening. When not writing about weeds, pests, soil, and growing plants, she's tending to her veggie garden and the lovely turf strip in her front yard.