‘Don’t fertilize your lawn in the fall, because you don’t want to get your grass growing before winter arrives’
Fall lawn fertilization does sound a little counter intuitive. After all, why on earth would we want to ramp up growth in the fall, just as our lawns are trying to hunker down for winter? But fall fertilization — done properly — will keep your grass happy during winter and get it off to a roaring start in the spring.
A bit of science
During spring and summer, we fertilize our lawns to enjoy the beauty of dense, rich, green grass blades and feel their luxurious softness under our feet. But once fall arrives fertilization takes on a completely different role. As the days shorten and the temperatures drop, rather than pushing a bunch of top growth on our lawns, fertilizers are used to increase sugar storage in the grass crowns (base of the leaves). Robust, sugar-filled crowns are not only more hardy and disease-resistant during the winter, but they also green-up more quickly in the spring, giving our lawns a nice jumpstart on those loathsome weeds.
When the objective is crown building rather than stimulation of leafy growth you need to consider two things: the correct fertilizer and the right timing. Nitrogen — the first number on the label — is king when it comes to increasing sunlight-harvesting chlorophyll in grass blades. More chlorophyll simply means more stored sugars in the crowns.
Avoid high-phosphate fertilizers (middle number) because established lawns require surprisingly little at any time of the year, let alone in the fall. Plus, phosphate is the main culprit responsible for algae blooms in lakes, rivers and ponds. Still, if you find that phosphate is deficient in your lawn, apply it in the spring when there is less risk of the fertilizer prills being washed off the turf.
When it comes to timing, you don’t want to apply the fertilizer too late in the fall, or it’s largely wasted. When nitrogen rests on the soil surface, it can ‘volatilize,’ which is just a fancy term for your precious, solid nitrogen prills converting into gas that, quite literally, evaporates into the air.
A good target time for nitrogen application in our region is about three weeks prior to the ground freezing up. Grass blades cease growing with about five consecutive days of temperatures in the 7 to 10 degrees Celsius range, accompanied by nighttime temperatures at or below of minus-1 degrees. So when does that occur in our region? Mother Nature is rather capricious at the best of times, particularly in our part of the world, but I’ll take a stab at it and say that a good target time to commence fertilization is usually around the second week of October.
What should you do?
Select a fertilizer with a high nitrogen percentage like 46-0-0 and keep it handy.
When applying the 46-0-0, apply it with a good broadcast spreader and apply half the recommended rate of fertilizer in a north/south direction, followed by half the rate in an east/west direction. The crosshatch pattern provides much better distribution of the fertilizer and reduces the risk of burning your lawn.
If you still find the concept of fall lawn fertilization tough to wrap your head around, just think of your lawn as being somewhat analogous to a bear. Just as a bear benefits by consuming a bunch of extra calories before its long winter hibernation, so too does your lawn. Unfortunately, as we all know, that same strategy does not work particularly well for members of our species.
Jim Hole is the owner of Hole’s Greenouses in St. Albert and a certified professional horticulturist with the American Society for Horticultural Science.
Article by Jim Hole for the Edmonton Journal, https://edmontonjournal.com/life/homes/gardening/fall-fertilizing-can-aid-your-lawn-through-the-winter, re-posted by Pacesetter Homes