Four conditions take the bag off the table. Keep it in the shed on a drought stressed lawn, on brown dormant turf, on grass you seeded this season, and on any day when rain is due inside 24 hours. You want to avoid weed and feed in those windows for one plain reason. The bag does two jobs in one pass, and neither half works unless the lawn has water in it and is pushing new blades.
"It rained on Tuesday, so the lawn is fine," my neighbor told me, spreader already loaded, in the second week of August. The turf had a gray cast and my footprints stayed put where I walked out to look at it. Down the strip that slopes toward the street drain it had gone the color of dry straw. Broadleaf herbicide does its best work on young weeds that are still growing, and nothing on that lawn was growing.
Dormancy and drought stress are two different problems, and the bag fails each one for its own reason. Brown grass that has stopped growing does not take up nitrogen. Dormant lawn fertilizer sits on the surface until the next rain moves the excess off your property. You pay for that nitrogen and the storm drain gets it, so the only thing you fed was the water your yard drains into.
A drought stressed lawn fails on the herbicide side of the bag. You should not treat one at all, because these products work best on weeds that are young and growing. A weed that has shut down in dry heat gives you poor control at full price. And the grass around it is already struggling, so you are paying for a treatment that will not work while you put more stress on the part you want to keep.
Rain is the easiest one to check and the one most people skip. The extension service at the University of Maryland says to hold off if precipitation is expected within 24 hours, unless your label says otherwise. A storm that afternoon washes the application off the leaves before it can do much of anything, and you get to buy the bag twice. The same guidance asks you to keep the mower parked for a few days before and after you spread.
- Growth: Look at the clippings from your last mow. An empty mower bag means nothing is growing, so both halves of the product go to waste.
- Color: A gray cast, or footprints that stay behind, means the lawn wants water and not food.
- Forecast: Read the next 24 hours of rain against what your label allows, then pick another day if the two disagree.
- Weed size: Look for small, young weeds. Tough old ones in a stressed lawn are a job for spot treatment later on.
- Count the mowings on a new seeding before any broadleaf product goes down.
New lawns have their own waiting period. Mow a seeded lawn at least three times before any broadleaf herbicide goes down, which lands roughly 6 to 8 weeks after the seedlings come up. Count the mowings rather than the days, since slow growth stretches that window out.
Two more lines on the label matter before you spread. Hold off on any nitrogen product until the soil at 4 inches (10 cm) deep stays at 65°F (18°C). And keep any mix containing dicamba away from the root zones of your trees and shrubs, because the roots pull it in and it can injure them badly.
I always check for a week of steady growth after a good soak before I spread anything at all. If weeds get ahead of you while you wait, pull them or spot treat them, and avoid weed and feed until the whole lawn is back to growing. Grass that is growing takes up the nitrogen and weeds that are growing take in the herbicide, which is the only way one pass does both jobs.
Read the full article: Weed and Feed: When It Works and When It Fails
