Over-fertilizing your lawn can occur not only when you apply too much fertilizer, it can also occur in soil with poor drainage where fertilizer builds up, or when the lawn does not get sufficient water after fertilizing.
How Fertilizer Affects Lawns
Every lawn needs fertilizer. Think of your lawn as a crop that gets “harvested” by mowing, usually weekly. The grass is in a constant state of regrowth and for that to happen, the nutrients in the soil need to be replenished.
Don’t Fertilize Without a Soil Test
A soil test is crucial to determine how much fertilizer your lawn needs. Ideally, it should be a test done by a soil test laboratory that gives you a detailed analysis of the soil and recommendations for remedying shortfalls. When you send in your soil samples, make sure to specify that it’s for a lawn, which has different nutrient needs than a vegetable garden or a flower bed. Ideally, you should also specify the type of grass you have so the lab can give you specific recommendations. The soil test will tell you whether the nutrient levels in the soil are adequate and will recommend which nutrients you need to add. It will also give you information about the soil pH, which is another crucial factor because a low soil pH affects the availability of nutrients in the soil. The soil test indicates whether you need to correct the pH of the soil by adding lime. Once you have that baseline, you can use DIY soil tests or instruments with probes to monitor the fertilizer level in the years when you don’t do a soil test by a laboratory.
Slow-Release High-Nitrogen Fertilizer
Lawns need about one pound of nitrogen per 1,000 square feet. How this translates into the actual fertilizer amount depends on the percentage of nitrogen in the fertilizer. The higher the percentage of nitrogen in the fertilizer, the less fertilizer you need. Lawn fertilizers typically have an N-P-K ratio of 3-1-2 or 4-1-2. How the fertilizer is released is also important. Slow-release or control-release fertilizers are best for lawns as they supply it with a steady flow of nutrients over a longer period of time. Organic fertilizers are by nature slow-release. Also, not all nitrogen is created equal. Special lawn fertilizers contain water-insoluble nitrogen (WIN), which is a slow-release fertilizer. Look for a fertilizer with at least 50 percent WIN of the total nitrogen content.
Improved Resistance to Pests and Diseases
A properly fertilized lawn is more resistant to diseases and pests. For example, a lawn that is low in fertilizer is more susceptible to grub damage. The healthier the grass, the better it can withstand grubs feeding on the roots of the grass.
Proper Application of Fertilizer
If a lawn is low on fertilizer, you cannot catch up in a single application, you need to increase the fertilizer level gradually and in steps in order for the grass to absorb it. Fertilizing too much at once leads to over-fertilization and killing your lawn. Always apply granular fertilizer when the grass is dry. If the grass is wet from rain or dew, the fertilizer will cling to the blades and burn them.
Signs of an Over-Fertilized Lawn
The most obvious sign of an over-fertilized lawn is yellowing or browning of the tips of the grass blades and in severe cases the scorching of the entire blades. When the grass is on fertilizer overload and cannot absorb it all, it leads to varying degrees of burning. Other signs of over-fertilization are limp or black grass roots, or a crusty residue on top of the soil. Failure of the grass to grow, or grass growing very slowly after fertilizing, may also be a sign of over-fertilizing. When the grass dies, you’ll end up with bare patches in your lawn, requiring re-seeding before weeds take root.
Steps to Repair an Over-fertilized Lawn
Depending on when you realize that you over-fertilized your lawn, there are different steps to correct it.
Remove the Extra Fertilizer
If you accidentally spilled a large amount of fertilizer in a single area or spot, take immediate action to correct it. Rake it up as best as you can and remove it, or if collecting it is not possible, use a rake to distribute it as broadly as possible, and then water the area intensely to dilute the fertilizer.
Watering
Giving your lawn extra water helps to dilute and wash away the excess fertilizer. This remedy works best if done promptly after over-fertilizing but even if you already notice some browning or yellowing of the grass, water helps it to recover and bounce back. Water your lawn with a sprinkler and saturate the grass with at least one inch of water every day for an entire week, or until you see the grass bounce back.
Delay Mowing
The general rule of not cutting your grass short is especially important if you’ve over-fertilized your lawn. The longer the grass blades, the more photosynthesis takes place, which means the grass is growing more while absorbing more nutrients and thereby getting rid of the excess nutrients in the soil. So if you’ve over-fertilized your lawn, take a break in your mowing routine and let the grass grow for a few more days.
Reseed
If the over-fertilization is so severe that the grass dies, you’ll need to reseed the bare spots. First, water the area thoroughly as described above to get rid of the excess fertilizer. Fill the bare patches with top soil and use a cultivator to work it into the soil, then rake it. Sprinkle it evenly with grass seed, cover lightly with straw to retain moisture, and water it daily in the absence of rain until the grass is established.
How to Prevent Over-Fertilizing Your Lawn
Even if your lawn does not show any of the typical signs of over-fertilization, excessive lush growth from too much nitrogen can stress the grass in hot weather, lead to thatching, and pollute the ground water. To prevent over-fertilizing your lawn, it is better to use less fertilizer and apply it no more than twice a year, in the spring and fall, and never in the summer. One pound of nitrogen per 1,000 foot is the upper limit but there is no harm in using 25 percent or less fertilizer than indicated on the fertilizer bag, especially if you leave the grass clippings on the lawn. About half of the nitrogen that you have applied to your lawn can be in the clippings, and by leaving them on the lawn, you can cut down your fertilizer needs by 25 to 40 percent.
