Turf Article

It’s been a warm, wet fall for much of the eastern US this year, these are good conditions for applying a “winterizing” late-fall fertilizer to encourage root growth in our lawns. Fertilizing cool-season grass this month provides food that will be used for root expansion and food storage – for a strong lawn plus a quick start next spring.

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Although this timing for this fertilizer application can be tricky, under the right conditions this is a great way to improve your lawn’s health and potentially reduce your spring work-load all at once.

This fertilizer timing has previously been known as the “winterizer,” and in the “big box” stores you can still find fertilizer bags with this term on them. These fertilizers generally include a larger amount of nitrogen (25+) but are also high in phosphorus and potassium (7-20) because older university work showed a benefit to having all three nutrients, especially potassium, to help improve winter hardiness. However, recent research has been showing that nitrogen is likely the bigger workhorse in protecting grasses from winterkill and that the phosphorus and potassium, while useful, are not as beneficial unless they’re being applied to high maintenance turf (like golf courses and sports fields).

When is a late season application most likely to help?
It’s tough to get this application just right. In colder and drier years it’s even more difficult. This application is recommended if:
1) Your lawn is a cool-season grass, not warm-season. Warm-season grasses do not need any fertilization once average daytime temperatures drop below the mid-sixties (65° F).
2) The turf is still actively photosynthesizing: so daytime temperatures are above 40° F, conditions are not dry, the grass is still green in color (hasn’t gone dormant, there has not yet been a “hard frost”), and the soil has not frozen.
3) Mowing has stopped or drastically been reduced. This indicates the movement of nutrients and plant food into the roots rather than being directed into the leaves, which are not useful for surviving the winter or regrowing in the spring.

What is a hard frost?

Which fertilizer is best?
A mixture of slow and quick release nitrogen sources is a must for a late-season application. At least 50% quick release nitrogen ensures that your money is being spent on the current season- that the nitrogen will be immediately available to the grass for growing and storage in the roots, which is the main intention of this application. Additionally, having at least 25% slow release nitrogen reduces leeching if cold temperatures come earlier than expected or if the soil dries out.

Organic fertilizers are not recommended for a late-season fertilizer application. They are activated and made available through soil microbial action which is greatly reduced in cooler temperatures – very little nitrogen would be made available for turf use until spring is well underway, so both the late-fall and early-spring availability would be missed.

MyTurfandGarden.com has two excellent late-fall fertilizers.
Nutriscape 32-0-7 “Late Fall Fertilizer” is 50% slow-release N, with a small amount of potassium to encourage winter hardiness.
• To apply 1lb of N/1000ft2 plan to use 3lb of fertilizer/1000ft2.
• To provide .5lb of N/1000ft2 plan 1.5lb of fertilizer/1000ft2.

Nutriscape 25-0-15 “Early Fall Fertilizer” also has 50% slow-release N and though it is labeled as an “early fall” fertilizer it can also be used into late fall, especially for soils needing more potassium (have you had a Think-Soil™ test completed on your lawn? There’s still time this season!!)
• To apply 1/4lb of N/1000ft2 plan to use 1lb of fertilizer/1000ft2 .
• To apply 1lb of N/1000ft2 plan to use 4lb of fertilizer/1000ft2.

How much should be applied?
Most recommendations will note that “up to 1lb of Nitrogen per 1000ft2” can be applied at this time of year. Here’s a general set of guidelines to help you decide if you want to apply the full amount or less:
1) If 4lb of nitrogen or more has been applied to your lawn already this year it is may be better to skip this application or go with .25-.5lb N/1000ft2
2) If cold daytime temperatures are right around the corner (according to the local or national weather services), or if nighttime temperatures are already dipping near to freezing (32° F), apply .5lb N/1000ft2 or less
3) If you’ve been actively needing to mow your lawn every week or two in the last month apply 1lb N/1000ft2
4) If the local and national weather services aren’t predicting cold temperatures until December or late November apply 1lb N/1000ft2

Don’t make a late-fall application on sandy soils or lawns that are near water.
Sandy soils always have a high chance of leaching, and they leach even more in the when cold temperatures mean there are no actively growing roots to catch the nutrients before they run off or leach.