Lush, green lawns are the pride of every gardener, but sometimes too much fertilizer can do more harm than good. Over-fertilization is a common problem that causes yellowing and drying of grass blades, especially in spring. Learn how to recognize the signs and what you can do to prevent and fix this issue for a healthy, vibrant lawn.
If your lawn shows yellow leaves and blades in spring, it is often due to over-fertilization. Here’s how to solve and avoid the problem.
The green carpet (your lawn) is known to be quite nutrient-hungry. Still, it happens frequently that hobby gardeners over-fertilize their lawns because they mean well with nutrient supply.
How to recognize over-fertilization of the lawn?
When too many mineral nutrients enter the soil, the so-called osmotic pressure in the root cells reverses. Normally, the concentration of minerals inside plant cells is higher than in the surrounding soil—and this is essential for the plants’ water uptake. This happens through the physical process called osmosis: water molecules always move toward the higher concentration, in this case from the soil water through the cell walls into the root cells.
If the mineral concentration in the soil solution is higher than in the root cells due to over-fertilization with mineral fertilizers, the direction reverses: water moves out of the roots back into the soil. The result: the plant can barely absorb any water, leaves turn yellow and dry out.
At a glance: Tips against over-fertilized lawns
- Water the lawn thoroughly with a sprinkler
- Apply mineral fertilizers with the spreader at a lower rate than recommended
- Avoid overlapping passes when spreading lawn fertilizer
- Preferably use organic or organic-mineral products
The symptoms mentioned above also appear in lawn grasses when you have over-fertilized your green carpet. A clear sign of over-fertilization is yellow stripes in the lawn. These typically occur when using a spreader if the passes overlap, meaning some grass areas receive double the nutrients. Therefore, pay close attention to the tracks and leave some space between adjacent passes if necessary. The fertilizer dissolves in the soil anyway and usually distributes so that all grass receives sufficient nutrients.
How can you rescue the lawn after over-fertilization?
The most important measure against over-fertilization is thorough watering of the lawn. This dilutes the soil solution and reverses the osmotic pressure back to the proper direction. Additionally, some of the nutrient salts are washed away and moved into deeper soil layers where they no longer directly affect the grass roots.
As soon as you realize you have over-fertilized your lawn, set up a sprinkler and run it for several hours until the grass turf is thoroughly moist.
How to avoid over-fertilization?
Apply mineral lawn fertilizers in slightly smaller amounts. High-quality spreaders have a mechanism to precisely control the amount of fertilizer distributed. Choose the setting one level lower than what is stated on the fertilizer packaging. Also, as mentioned above, avoid overlapping the passes when applying fertilizer with the spreader.
Applying lawn fertilizer with a spreader
Tip: Use organic lawn fertilizers
If you want to be on the safe side, use organic or partly mineral lawn fertilizers instead of purely mineral ones. On one hand, they are better for the environment; on the other, at least the nitrogen content is organically bound—usually in the form of horn shavings or horn meal, sometimes also in vegan form as soybean meal. Castor bean meal is no longer used as a nitrogen source in most branded products today. It must be thoroughly heated before further processing into lawn fertilizer so that the contained toxins break down—otherwise, there is a high risk of poisoning for pets like dogs, who like to eat the protein-rich material.
If part of the nutrients in the lawn fertilizer—especially the nitrogen—is organically bound, there is hardly any risk of over-fertilization. It must first be broken down in the soil by microorganisms and converted into the mineral form nitrate—only then does it exert its osmotic effect.
Preventing over-fertilization is key to maintaining a strong, green lawn year-round. By applying fertilizer carefully, avoiding overlaps, and choosing organic options, you help your lawn thrive naturally. And if over-fertilization does occur, thorough watering can quickly restore your grass’s health—keeping your lawn looking its best season after season.
