Overseeding is one of the most important lawn care tasks, yet few homeowners ever do it. So, you ask, if I fertilize my lawn properly, why do I need to add new seed, especially if my grass looks pretty good right now? The answer is grass is not immortal. After five or six years, grass plants will slow down their reproduction rates; they get tired just like we do as we age. Thin grass invites weeds.
Overseeding compensates for that natural slow down of the turf’s reproduction. There are two major benefits to overseeding every five or six years. First, you insure your lawn stays thick and dense, or if it has thinned, you will make it thick again. Thick grass has few if any weeds if it is mowed over 2 inches tall.
The second benefit is disease resistance. The new varieties of seed you sow this year will have better disease resistance than those varieties already in your lawn.
Your goal is to have a lawn that is as dense as brand new quality sod. Go to the garden center selling sod and try to spread the grass blades to see if you can see any soil. Usually, the grass is so thick you cannot see soil of brand new sod. Now go outside and check your own turf to see if by spreading the grass blades you can see any soil. It is likely the soil will be readily visible. That means your lawn needs to be overseeded.