How to Fix an Overfertilized Lawn
There are limited options for preventing damage from overfertilizing a lawn. The good news is the best fix is a simple one. Washing the fertilizer through the lawn deep into the soil with water is the solution and can often prevent permanent damage. A result of excess fertilizer and drench watering will be fast blade growth, which means that increased mowing will likely be required for a month or so.
Water the lawn immediately after you discover that an excess of fertilizer has been applied. Water slowly and deeply over at least 30 minutes to wash the fertilizer off of the blades to prevent the most immediately visible signs of burn and preserve the green of the grass. Be sure to soak the entire area including the edges to wash out the fertilizer evenly.
Water the lawn again in two to three days and then twice per week the following week with at least two inches of water, 1 inch at each session. Always water deeply and slowly to percolate the fertilizer down into the soil as opposed to creating chemical runoff that occurs with heavy watering over a short period of time.
Wait to mow the lawn two weeks after the fertilizer mishap. Mowing immediately after can expose the blades and fertilizer, creating burn spots. Mow only dry grass, and remove only one-third of the blade height with each mowing session to reduce stress. Remove more blade height by lowering the cutting blade with successive mowing sessions.
Fertilize Your Lawn By Hand
Fertilize when the lawn is damp but not soaked, such as in the morning when dew is present or after a light rain. Avoid fertilizing before or after a heavy storm when the fertilizer can be washed away and wasted. Calculate how much fertilizer you need to spread over the entire lawn, prepare that amount and divide it in two so you can spread it in two separate passes. Start fertilizing at one corner of the lawn. Walk backward from that corner in a straight line while reaching into the bucket, grasping a handful of fertilizer and spreading it with a sweeping motion. Water the lawn after you've finished fertilizing to wash the chemicals off the grass and help them soak into the soil.