Fertilizer burn is caused by chemical fertilizers whose minerals are all in salt form — when you apply too much chemical fertilizer to your lawn, these salts dry out, and can sometimes even kill your grass and plants. It can take the form of a general discoloration throughout a lawn or garden area, or else, you'll be able to see overlapping strips and patches of dead or dying grass and plants. Though there are preventative and recovery methods that can save your grass and plants, you should remember that the recovery of your lawn also depends on the amount and type of fertilizer you used, the amount of moisture available, the health of your grass and plants before they were affected, as well as how quickly you act in attempting to rescue your lawn.
The use of excessive nitrogen in fertilizer is the quickest and most obvious way to burn out your grass. Though, some organic fertilizers that contain dried blood, urine, or fish emulsion may also cause fertilizer burn to a lesser degree. In general, though, you have a much better chance of avoiding fertilizer burn using organic fertilizer than chemical because they work by being broken down over a longer amount of time by soil microbes.
It's advised that you not apply fertilizer to your yard during high daytime temperatures, which can accelerate any burn potential. Pay attention to any application instructions that come with your fertilizer, especially if you have an especially potent balance or strength. In general, you don’t want to put too much stress on your lawn, meaning that you never want to overfeed your lawn, especially if it’s newly transplanted or affected by drought, heat, or disease.
If you’ve accidentally overfed your lawn, the first thing to do is to try and scoop as much of it as you can before it dissolves—a broom, dry or wet vac will work. If you’re past this stage and the fertilizer has already dissolved, try and flush it out with water. Use sprinklers, hoses, and anything else that works and proceed to water until your soil literally cannot absorb any more water. For the next week after that, water once a day during the morning so as to avoid having to combat heat and potential fungal diseases. After you’ve done that, you’re essentially going to have to wait till the next planting season to see if there was any effect and if it’s safe to re-plant. However, in the early spring, you might notice a difference sooner than that. You’ll definitely also want to overseed thin areas while sowing seed or sod in the affected spots.
An alternative to flushing excess fertilizer out with water is to apply agricultural gypsum to your soil. This is a less common and possibly less effective method, as once you apply gypsum, your whole soil’s chemical composition changes entirely, as it replaces minerals with calcium. It’s advised that you first apply a laboratory test to your soil to see if that makes sense for your specific soil. Generally speaking, it’s not a great idea to stop a chemical problem by using more chemicals. You’ll definitely want to at least try the water method first.