Weed and feed products do kill broadleaf weeds and they do green up your grass, so the bag is not lying to you. University of Maryland Extension still does not recommend them for routine lawn care, and it gives three reasons. Not one of the three is that the chemicals fail. The objection is to what a single bag makes you do to your whole yard at once.
"Just buy the one with the fertilizer already mixed in," my neighbor tells me over the fence. I have watched him run that same bag every April for years, and his lawn does look decent from the sidewalk. To reach the dandelions in four or five spots, though, he treats every square foot he owns. The food half of the bag lands in April, when his grass wants it in fall.
It Treats The Whole Yard
- Coverage: Fertilizer has to go down evenly to do its job, so the herbicide blended into it goes down evenly too.
- No aiming: A spreader cannot steer a granule toward one dandelion, so your clean turf gets the same dose as the weedy patch.
It Lands In The Wrong Season
- Spring drop: These bags are applied in spring, which is when the weeds are the reason you bought one.
- Grass clock: Most lawn fertilizer belongs in autumn, so the food shows up months off schedule.
It Can Overfeed The Lawn
- Stacked nitrogen: A spring feeding piles on top of whatever else your lawn gets that year.
- Set rate: The bag decides how much food your grass receives, not a soil test or the color of the turf.
Start with the coverage problem, because it is the one you notice least. You buy enough herbicide to cover your entire lawn so you can kill weeds that sit on a tiny fraction of it. The strip along your driveway never had a weed in it and gets treated anyway. So does your shady corner, and so does the ground under your maple, and that last one matters more than it sounds.
Weed and feed timing is set by the bag, not by your grass. These products go down in spring, whatever the lawn happens to need that year. Your fertilizer rides along on that same calendar. Your lawn runs on a different one. A spring feeding stacked on the rest of the year's nitrogen is a common route to an overfertilized yard, and that is the third objection on the list.
There is a risk the front of the bag skips. Dicamba can damage your trees and shrubs when their roots take it up from a treated lawn. Those roots run right under the turf you just fed. It takes very little to do visible harm, either. Growth-regulator actives such as 2,4-D and dicamba deform tobacco, grapes and tomatoes at 1 ounce per acre (70 g per hectare).
Split the bag into its two jobs and both get easier to do well. Feed your lawn on its own schedule, with most of the food going down in fall, at the rate your soil test asks for. Then handle the weeds you actually have. Spot treating lawn weeds takes a hand sprayer and a slow walk around the yard. You hit the plants you are aiming at instead of thousands of square feet of grass that was doing fine. On most lawns that is a few dozen plants.
Treat only when your daily air temperatures will stay between 65°F and 85°F (18°C and 29°C), and leave a drought-stressed lawn alone until rain brings it back.
Read the full article: How to Choose a Weed Killer That Actually Works
