If the lawn is over-fertilized, unsightly discolouration and bare patches will result. Find out here what you can do about it and how to avoid over-fertilization.
If the carpet of lawn appears yellowed and unappealing in spring, the suspicion arises that the green area is lacking in nutrients. In most cases, however, the opposite is the case and the hobby gardener simply meant too well with the fertilization last season. Too much mineral lawn fertilizer can lead to discoloration, bald spots and other blemishes.
Here's how to spot an over-fertilized lawn and what to do about it.
What happens if you over-fertilize?
If the soil is oversaturated with minerals, the osmotic pressure in the root cells reverses. Osmosis describes the movement of liquid through the soil into the root cells and the highest concentration of minerals. Plant cells normally contain more minerals than the substrate. This condition is important to ensure that the plants can absorb liquids. If the soil has more minerals due to over-fertilization, this process is reversed. The water then withdraws from the roots back into the earth. The plants now lack moisture, causing them to turn yellow and dry out.
How to identify overfertilized soil?
You'll see if something isn't right in your lawn. You can probably see yellow stripes. This happens when you have used a spreader for fertilization. Exactly what the damage looks like depends on which nutrients are in excess.
| Nutrient Oversupply | Damage |
| Nitrogen | • Leaves brittle or swollen • Dying of roots • Dark green discolouration • Susceptible to fungus • Susceptible to frost damage |
| Phosphate | • barely visible traces • groundwater pollution possible |
| Potassium | • growth inhibition • dead leaf tips |
| Magnesium | • Growth inhibition •dead leaf tips |
You don't have to do anything in the case of slight over-fertilization. The lawn will regenerate itself and does not need any additional fertilizer in the current season.
Burns in the lawn?
If the lawn looks burnt, this is a typical sign of exosmosis, the reversal of liquid absorption already described. The over-fertilized grasses first turn yellow, later turn brown and finally die. This can certainly happen over a large area and therefore suggests burns.
A similar damage to plants can also be caused by the use of road s alt. Because some hobby gardeners often take advantage of this when fighting weeds on sidewalks.
What to do against over-fertilization?
❍ remove visible fertilizer granules:
It can also help to remove the visible fertilizer grains with gloved hands. The fertilizer granules can also be raked out of the ground with a rake.
❍ seed new lawn in gaps:
If the lawn has been subjected to additional mechanical stress by pets or birds, you can repair it by sowing new lawns. So that the gap in the lawn can be closed as quickly as possible, it is best to use fast-germinating seeds such as Festuca rubra or Lolium perenne.
❍ Water lawn heavily:
The aim of the measures is to bring the osmotic pressure back into balance. The best way to do this is to thoroughly water the lawn. Diluting the substrate means that the majority of the nutrients are shifted to the lower layers of the soil and can therefore no longer have a direct effect on the roots of the grass.
Tip:
Set up a sprinkler and run it for several hours to thoroughly wet the lawn. You won't get very far with a watering can on a heavily over-fertilized lawn.
How to avoid over-fertilizing the lawn?
❍ Use Spreader:
Less is more - this actually also applies to lawn fertilization. It is often difficult to estimate the necessary amount by hand. Therefore, the use of a spreader is particularly useful on larger lawns. However, in order to avoid the aforementioned yellow stripes on the lawn, the paths of the spreader must not overlap.
❍ use organic fertilizer:
The damage described is caused by mineral lawn fertilizer. who uporganic fertilization of the lawn can prevent over-fertilization by reversing osmosis. Organic fertilizers are compost, horn shavings, horn meal or soybean meal. With organic fertilizers of this kind, the risk of over-fertilization is of little concern. In order to influence osmosis, the fertilizer would have to be broken down by microorganisms and converted into nitrate.