Weather plays a big role in all kinds of lawn care projects. From when you mow to the best time to reseed, the forecast often drives the project. The same is true for applying lawn fertilizer. Whether you are applying fertilizer in the fall—the best time to fertilize—or broadcasting fertilizer in late spring, soil moisture is a critical factor in timing it right. We tapped the experts to determine whether fertilizing before or after the next measurable rain is best. Their recommendation will simplify your fertilizer plan and lead to a healthy, strong carpet of turf.

Time It Right

Timing is everything when it comes to fertilizer application. Plan to spread fertilizer when the soil is warm and the grass is actively growing.

“Soil temperature really does matter,” says Lou Manfredini. “You want the soil temperature to be at least 50°F. This will help fertilizers and weed control to work its best.” When you apply fertilizer to turf that is dormant and not growing due to cold conditions or drought, it is wasted because the plant is growing so slowly that little of the fertilizer is absorbed.

Fertilizer timing also comes into play with the frequency of application. Spread fertilizer too frequently, and the lawn will grow wildly above ground while the roots struggle to keep up with all the shoot growth. Timing is everything.

Watch the Forecast

Before fertilizing actively growing grass, check the weather report. Turf fertilizer is available in granular (dry) and liquid formulations. Recommendations for when to apply vary slightly based on the fertilizer formulation.

If you are using granular fertilizer, Aaron Steil says, “Do not fertilize if moderate to heavy rains are likely within 24 hours.” He goes on to explain that the rain will wash away much of the fertilizer before the lawn can use it. The nitrogen-dense fertilizer will flow into waterways, disrupting the local ecosystem. Granular fertilizer can be spread if a light rain measuring a quarter-inch or less is forecast in the next 24 hours.

Lou Manfredini says fertilizing on a rain-free day is especially important when using liquid fertilizer. “Apply liquid fertilizer and wait about 24 hours before watering or a rain event,” he says. Manfredini says rain shortly after application will quickly wash away the valuable fertilizer before it can reach the turf’s root zone.

Bottom line: It’s best to fertilize your lawn after a rain. The moist soil will help the fertilizer break down more readily, delivering valuable nutrients to turfgrass roots without the threat of the fertilizer washing away.   

Water Granular Fertilizer into the Turf

Granular fertilizer does not begin delivering nutrients to plant roots until it is in contact with the soil and moisture. For that reason, many granular turf fertilizers must be watered in after application. Check the fertilizer package label for how-to information.

Beware of Burn

If your lawn has brown stripes or patches shortly after fertilizing, the cause might be fertilizer burn. Many fertilizers are made up of soluble salts. When the salts are heavily concentrated around grass roots, they pull water out of the plant, often killing it. Fertilizer burn is most common when the turf is fertilized in hot weather or without being watered in. Always water in fertilizer to prevent burning unless the package label directs not to.