Fall Lawn Maintenance: Overseeding

Now that we have dethatched and aerated, the next step in our fall lawn care regimen is overseeding. Let me stop here and say that some lawn care professionals do not agree with that order and suggest that you overseed before aerating. The theory behind this is that the holes created by aeration are too deep for seed to germinate and that a significant amount of seed spread on an aerated lawn will fall into those holes and be wasted. I have tried it both ways and for me seeding after aerating has been more effective, but either way will work perfectly well for most situations. I am also going to lump pH testing and lime application in with overseeding because, again, for me that has been most effective.

Applying lime is one of the more commonly misunderstood lawn care tasks. In this part of the country (Carolina Piedmont) many professional lawn care services routinely spread lime in the fall because our heavy clay soil tends to be slightly acidic. In most cases this approach does little harm and probably some good, but the proper way to determine whether your yard requires an application of lime and the appropriate amount is to conduct a pH test -- a test to determine whether your soil is acidic, neutral or alkaline. Soil test kits can be purchased for less than $10 at most garden centers and hardware stores. You can also send your soil sample to your agricultural extension office (for a fee) and they will provide a more accurate and detailed soil evaluation. Each method has its own specific instructions, but typically involves taking 3-5 samples from various places in the lawn, mixing them together, letting them dry and then doing a chemical test. Most grasses do best in soil with a pH of 5.5 to 7. Soils which are too acidic (below 5.5) will require an application of lime. In the somewhat rare case, in these parts at least, that your soil is too alkaline (above 7), you will need to add sulphur. The amount of amendment to add depends on the degree to which the soil is too acidic or alkaline, with a general rule of 50 pounds per 1,000 square feet of lawn for mildly acidic soils. More strongly acidic lawns may require multiple applications; one in the fall and one in the spring. It is important to note that soil pH does not change immediately upon application of the amendment and may take up to 6 months, so performing another test a week or two after application is useless.

Once you have determined the pH of your soil and added amendments as appropriate, you can overseed. This can be done on the same day or a few days later, as applying lime will not impact the germination or growth of grass one way or the other in the short term. We overseed because grass, although a perennial, has a lifespan and needs to be replenished. In nature, turf type grasses propagate by dropping seeds from tassel-like pods, constantly reseeding themselves. Since we keep our lawns cut to a height that does not allow them to go to seed, wee need to mimic that process by spreading seed on our lawns in the fall or spring; a process that has become known as overseeding. In most instances, you will want to overseed with the same type of grass that is currently growing, although there are specific circumstances that are beyond the scope of this article in which an annual grass type might be seeded over a perennial grass.

Apply the new seed with a drop or broadcast spreader, following the product's recommended coverage rate for the type of spreader you're using. Although not necessary, you can use The back side of a garden rake on bare spots to help work the seeds into the soil. It's ideal to overseed during a cool, wet period, but we cannot control the weather. For best results, keep the soil moist until the seeds germinate; a week or two. We finish up next week with an application of winterizing fertilizer.