After a rain it seems like all the imperfections show up in our lawns. Fixing them usually requires patience and the remedy varies depending upon soil type, time of year and grass species.
Repair options can be gradual. This is usually my favorite option. If the ponding area isn’t too deep and the existing soil texture is sandy, like it often is in eastern North Carolina, I like to use successive thin layers of washed sand. By thin layers I mean no more than a quarter inch or so at least two weeks apart.
If you go on the internet most literature tells you that straight sand is the wrong way to go. That’s true if you have a fine textured soil. Contrasting soil textures can worsen drainage. Water sits on top of the clay soil and saturates the sand. The area doesn’t drain.
I call it the bathtub effect. The same problem happens when installing shrubbery in clay soil. Most folks think that adding potting soil or sand to the hole will help. The opposite is true.
On sandy soils if sand is added and clippings are incorporated through regular mowing, grass will respond well. The key is not to get greedy and add too much at a time.
Adding too much topsoil with finer particles in it can suffocate a lawn as the existing grass has a tougher time penetrating it. The result is a patchy muddy lawn. Since sand is looser, slightly excessive applications are less severe.
On clay soils, mixing organic matter with dry loam and spreading thin layers on the low spots can help. However, the layers of topdressing must be thin. It will take a while to achieve perfection. If that’s not satisfactory, possibly major renovation is the only option.
Regardless of the soil mix, when top dressing, the grass must be actively growing. Now is a good time to topdress a fescue lawn. Late September is not a good time for warm-season grasses. It’s not a good time to replant them either. Warm season lawns should be addressed in late spring.
When applying any type of topdressing it’s important that weeds are not introduced. I like coarse builder’s sand because it’s most likely to be inert. Mixing that with good quality potting soil or peat moss will also result in fewer weeds than topsoil.
Often, low places in the lawn often become weedy because the grass is stressed. If this is the case, filling the dip won’t solve that problem and serious renovation is necessary. This is also when you could address the soil texture problems.
When doing serious renovation, amending the soil is fine if you incorporate the amendments. In other words, if your soil is clay you can add a sandy topsoil to it, provided you mix it well. The same goes for the sandy soil.
Your lawn will probably look patchy for a while. If that’s unacceptable, your only recourse is to start from scratch, at the proper time of year for the entire lawn.
Ted Manzer teaches agriculture at Northeastern High School (firstname.lastname@example.org).