Ready, set, grow: Weed & Feed correctly
Published 12:03 am Wednesday, April 3, 2019
Without a doubt, “weed & feed” products are one of the most popular lawn items sold and used in spring.
Popular thinking must be that they’re excellent products; after all, the name rhymes. (Turkey jerky, anyone?)
They can be quite useful and likely represent your best option right now to address two lawn issues simultaneously.
My only complaint is that the timing for the two products included — fertilizer and herbicide — don’t line up well. The best time to apply cool-weather weed killers is late January or early February.
That kills things like annual bluegrass and lawn burweed before they mature/toughen and before they can make seeds.
Besides having a great effect on their propagation, the lawn burweed (AKA sticker grass, picker grass, etc.) seeds are quite a nuisance.
But winter was too wet to apply lawn chemicals anyway, so there that went.
Now (late March through April) is a good time to fertilize. Much earlier and it would have been mostly, if not entirely, wasted.
A good rule of thumb is to fertilize after you’ve mowed twice. That way, you know the lawn is well out of dormancy regardless of the date.
If you’re using a weed & feed combo, directions on the label will tell you how much to use per square footage given what kind of grass you’re trying to grow. This will be based on the rate of herbicide but let’s assume that gets us approximately the right amount of fertilizer too.
You’ll want to fertilize again in about two months, so mark it on the calendar.
So how much? A heavy feeder like Bermuda (rare except athletic fields) wants 3-4 pounds of “actual” nitrogen per thousand square feet per year. St. Augustine (our most common) takes 2-4 pounds; zoysia 2-3 pounds; and centipede a measly 1-2 pounds.
These amounts are best split into 2 or 3 applications per year, about once every other month through August. (Don’t fertilize after August or you’ll invite brown patch and winter cold damage.)
So notice the word “actual” up there in italics. This is NOT pounds of fertilizer. A bag of fertilizer will have three numbers on it; indicating the concentrations of nitrogen (N), phosphorus (P), and potassium (K).
Those numbers tell how much N, P, and K are in the bag, in that order, by percentage. So a 15-5-10 (a good ratio for most lawns, absent a soil test) has 15 percent nitrogen.
To put it another way, it’ll take 6.67 pounds (feel free to round off) of this substance to equal one pound of actual nitrogen.
In case you didn’t retain all Mrs. Deroche’s Algebra from high school, divide 100 by the first number (again, N) on the bag. That will tell you how much fertilizer will give you one pound of nitrogen, therefore how many pounds of fertilizer to apply per 1,000 square feet.
So back to the weeds for a moment. The aforementioned weed & feed will sure enough kill most weeds currently present. There are a few different chemicals included in different brands, but most have atrazine.
Once watered in, it has a broad range of targets. This will give you a little residual control toward newly emerging weeds as well.
But I do suggest also using a pre-emergent herbicide (Preen, Amaze, or other brands). You can apply it about every three months to prevent — rather than fight — seasonal weeds.
If you want to know more about gardening, landscaping, or anything else horticultural, contact the St. John, St. James, & St. Charles Parishes County Agent André Brock at firstname.lastname@example.org. Also, the LSU Ag Center’s website can be accessed at lsuagcenter.com with lots of user-friendly information, including this article.