Fall Fertilizing or "Winterizing" Explained

Although the autumn equinox (fall) isn’t until 2:50 a.m. Mon., Sept. 23, it seems that Mother Nature has not started adjusting for it just yet, with high temperatures still in the 90s for the past week.

Nevertheless, that has not changed my contention that you can get busy now with autumn projects that involve landscape work and lawn care. Chief among those is the fall lawn feeding or “winterization.” There is no time like the present, since the soil is still moist from this week’s tropical disturbance.

I’ve told GardenLine listeners the story of a nursery owner who, around 15 years ago, berated me for calling it “winterizer,” because of our area’s dominant St. Augustine lawns. He would insist that it was simply a “fall feeding.” Of course, I always pointed out that he sold products that were labeled “winterizer.” Anyway, he’s no longer in business or around to beat me over the head with that anymore. In reality, though, he was technically correct - the “winterizer” term was originally meant for northern turfgrasses. Still, I have no problem with a “winterizer” for everything from St. Augustine to Zoysia to Bermuda.

Simply stated, a winterizer is designed to slow down the growth of grass prior to potential freezing weather and to beef up levels of potassium (the “K” in the N-P-K ratio). So, if you look at the various fall fertilizers out there, you’ll understand why I’ve been a long-time proponent of one in particular: Nitro-Phos Fall Special 8-12-16.Spring and summer fertilizers are typically 19-5-9s or 19-4-10s. But the last number - the potassium - in the 8-12-16 is “beefed up.” That heavier-than-normal dose of potassium should toughen up the plant tissue for freezes, a lot like antifreeze in a car’s radiator.

But here’s a big warning - and why I’m diving into winterizer numbers for the Gulf Coast: You can’t just go by the words “winterizer” or “fall fertilizer” on the many products out there. First, make sure it’s specifically designed for southern grasses (St. Augustine, Zoysia and Bermuda). Many “winterizers” from national companies are, in my opinion, anything but true winterizers. I’ve seen supposed winterizers with ratios like 30-0-5. Yikes! That’s way too much nitrogen (the N in N-P-K) to slow down growth, and actually very little potassium.

Too much nitrogen in our humidity, coupled with excess moisture, is an open invitation to brown patch. In fact, it’s almost like adding fuel to the fire during a brown patch explosion.

Here’s one absolute in this area: Avoid any “winterizer” if the first number (the nitrogen) in the ratio is more than 20.

For reference, here are the winterizers I have recommended for years:

  • Nitro-Phos Fall Special 8-12-16
  • Easy Gro Winterizer & New Lawn Starter 18-6-12
  • Ferti-lome Winterizer 10-5-14 or 10-0-14

If you’re thinking of using an organic fertilizer for a fall feeding, remember that they are just that … a FEEDING! For the most part, they are great for adding organic matter to the soil and giving the grass a small feeding. But they are not formulated with those higher-than-normal potassium levels for freeze protection. That doesn’t mean, however, they’re not a great way to prepare the turf and its soil for the winter months. Here are good examples:

  • MicroLife 6-2-4 (Green Label)
  • Nitro-Phos Sweet Green 11-0-4
  • Nature’s Creation 6-1-2 or 4-2-2, both with mycorrhizal

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