No, not if a storm is close. Spread a granular product a few hours ahead of a downpour and you watch the prills wash toward the storm drain instead of settling into your weeds. Do not apply when precipitation is expected within 24 hours, unless your label says otherwise. That label line matters, because a few products are built to go down and get watered in right away. So the short answer on weed and feed before rain is to wait a day. The longer answer depends on which half of the bag you care about most.
Rain is not one single risk, because the two halves of that bag want opposite things from you. The broadleaf killer is a postemergent, and it has to sit on the leaf and soak through the surface before it can move. A rinse an hour later strips it off before it does any work, and you have to buy and spread the whole thing again. Your preemergent is the other case. That one has to reach the soil, and water is what carries it there, so a shower is help rather than harm.
Watering in herbicide is its own step in the job, and you should plan for it. Soil-applied products need to be watered in by rainfall or 15 to 20 minutes of irrigation, which is a light, steady drink and not a storm. A gentle shower after your preemergent goes down does that part for you. A cloudburst does something else. Water that lands faster than the soil can take it runs across the surface and carries the product sideways with it.
Check the forecast before you fill the spreader. If rain is likely inside 24 hours, leave the bag on the shelf, unless the label tells you to water the product in.
Granular herbicide runoff is what reaches your beds and the yard next door. Dry granules flow off treated areas in irrigation or stormwater, and they injure downhill plants where they settle. A slope raises your odds of that and so does pavement, since a driveway hands the prills a clean path straight to the curb. Aim your spread pattern away from hard surfaces and away from the low corner of the yard where water always collects after a heavy night.
The fertilizer side of the product wastes your money in the same way. Fertilizer the grass never takes up runs off with the water, and it turns into groundwater pollution instead of green growth. You already paid for that pass across the lawn, and you paid for the fuel and the hour it took you. Rain that lands too early sends a good part of it to the storm drain, and none of it comes back to your grass.
Temperature sets the other window you have to hit. Postemergent broadleaf products go down at daily air temperatures of 65 to 85°F (18 to 29°C), so a cold snap and a heat wave both work against your pass. Granules also want moisture on the blade. Spread them on moist, dew-covered foliage for the best control, which is one more reason your early morning beats your afternoon.
Your routine takes about two minutes. Open the hourly forecast and look for a dry stretch that runs at least 24 hours past your start time. Then read the label, since one line there can override everything above. Spread while dew is still on the grass and keep the sprinkler off it afterward. And if a storm shows up ahead of schedule anyway, count the pass as lost and treat again once your forecast clears.
Read the full article: Weed and Feed: When It Works and When It Fails
