For the purposes of overseeding lawns we're either filling in bare patches, strengthening weak spots in the sod or preparing a lawn for Winter. Choosing the right lawn seed for our lawns becomes easier with these factors in mind.
Mixtures of seeds are most often done so that each grass type can compliment the other, when one grass type does less well in shade for example, a complimentary grass type is chosen which excels in low light conditions.
Evaluate Existing Lawn Conditions First
If the existing lawn is doing well and has been doing well for many years then there is little point in changing the grass type, or grass types if a blend is being used to what is already in place. To overseed a lawn which has always done well, simply use the same seed that was used to establish the lawn.
If the lawn is struggling with low water from drought or water restrictions, or if it's doing poorly in the shade, then choosing a different grass type to overseed with would best correct any problems the lawn is experiencing.
Tall Fescue is best known for its heat and drought tolerance, if lack of water or heat is adversely affecting your sod then Tall Fescue could be the answer to overseed with. Tall Fescue has medium width leaf blade, has a rich dark green color, and is increasing in popularity with new cultivars marketed as "Armada" and "Eco Lawn Fescue". The downside of Tall Fescue is that it can sometimes be more prone to lawn fungal diseases such as Leaf Spot, but with proper care and maintenance - this can be reduced and even cured with Fungicides.
Tall Fescue should not be mixed with Kentucky Bluegrass, as the difference in appearance, and most notably their difference in heights can cause a slightly unusual looking lawn to develop.
The Fine Fescues are very popular choice for blending with the more popular Cool Season grass types, With Red Fescue being the most popular due to it's look and feel, creating a lovely soft turf when being used as a companion to Tall Fescues and Kentucky Bluegrass. While Hard Fescue and Chewings Fescue are chosen more for their increased shade tolerance.
Perennial Ryegrass is the most popular turf type to blend with other types of grass. The ability of Perennial Ryegrass to easily blend into many other turf types is well known, and it's tolerance for shade, ability to withstand minor drought conditions and it's quick establishment are the many reasons it's become such a popular companion grass.
Kentucky Bluegrass is more often known as a primary grass choice for use as lawns, in fact it's the most popular grass type on the continent, and there's very good reason for this. Kentucky Bluegrass makes one of the best all-round lawn types for most cooler regions.
This popularity as a primary lawn makes overseeding with Kentucky Bluegrass less common, because when overseeding is done with a different grass type it's often done with Bluegrass as the primary lawn, and the homeowner is trying to overcome a weakness found with the grass, such as shade, disease or drought.
If the homeowner is reseeding with Bluegrass to simply thicken up the sod, Bluegrass performs best in full sunlight, is a little slower than other grass types to establish. The homeowner should see results of good thickening after 2 to 3 months.