The last thing you want is for your lawn fertilizer to wash away or produce ugly burns instead of benefitting your grass. Watering your lawn immediately after you apply fertilizer is the best way to prevent problems, but in most cases, you can wait until the end of the day without risking the health of your lawn.
Fast-acting ammonium or urea fertilizers are prepared using water-soluble salts that only mix with the soil after becoming wet. The optimum time to water your lawn after applying dry fertilizer is just after you finish distributing it. Spreading fertilizer on damp grass or allowing the grass to get wet before the fertilizer has washed into the soil might harm your lawn. Although the best practice is to water fertilizer into your lawn immediately after you have applied it, you can wait up to 24 hours after fertilizing before you water during cool weather or if you are using a slow-release fertilizer. Watering quickly after spreading fertilizer eliminates a variety of issues that worsen as the fertilizer lingers on the grass.
Leaf burn is caused by fertilizer that combines with water but is not rinsed off your lawn. Fog and dew that form in the evening and early morning provide enough moisture to combine with the salt in the fertilizer, allowing your grass to absorb it through its blades. If your lawn is heat strained, leaf burn may occur after fertilizer is sprayed and soaked into the soil. If your lawn is not adequately watered, salt buildup in the soil may cause patches to dry up. Most lawns need 1 inch of irrigation water or rainfall every week to avoid dehydration.
When the air temperature exceeds 85 degrees Fahrenheit, fertilizers left on the ground begin to volatilize and the risk of fertilizer burn increases. Over time, the nitrogen in your fertilizer escapes into the atmosphere as a result of this process. The longer your fertilizer stays on the grass without being watered in, the worse the issue grows. Volatilization is a relatively slow process, but it will begin to have a significant effect on your fertilizer if it is left exposed to the air for a long period of time.
Mild rainfall may wash fertilizer into the soil, but strong rain after you’ve applied fertilizer might wash it off your grass rather than mixing it in. If you leave fertilizer on your lawn for many days without soaking it into the soil, you risk losing part or all of your fertilizer to the first hard rain that falls on your grass. This discharge, in addition to wasting your time and money, may damage adjacent rivers.