Spring is the time to make certain that bare and thin spots are top-dressed and over-seeded in the Northeast. In an all natural organic turf care approach a dense stand of turf grass is the best defense against weeds. This is especially true when trying to make improvements to the underlying soil conditions. As such I strongly discourage trying to establish a new lawn or perform major lawn renovations in the spring.
Bare soil = Weeds. The faster you can fill in your turf the better off you will be. For that reason I recommend over-seeding those bare spots with perennial ryegrass. Perennial ryegrass will germinate in approximately three to ten days. Kentucky bluegrass can easily take twice as long if not longer; germinating in six to twenty-eight days. As such Kentucky bluegrass will not be established soon enough to provide us with the desired weed protection.
Keep in mind that soil temperature affects seed germination. Seeds will not germinate until the soil temperature reaches 50⁰ or greater. Soil temperatures tend to be roughly 10⁰ lower than the air temperature.
The easiest way that I have found to fix those bare spots is fill a wheelbarrow half full with a good loam/compost mixture, roughly 60/40. To the loam/compost add a half gallon of seed. A plastic juice pitcher works great for this purpose. Then use an iron rake to mix the seed with the soil in the wheelbarrow; just like you would do if you were mixing cement in your wheelbarrow. Once you’re sure you have good seed to soil contact in your mix simply go around to those bare spots and dump or shovel your mixture onto the bare spots. Use a spring rake to then smooth out the soil.
Be sure that these areas get adequate water until they are established. I recommend watering twice a day for approximately ten minutes at a time.
All of the above should be accomplished before May 15th. Then allow all your turf grass to grow as high as acceptable. I have found excellent results from mowing at 3 ½“– 4”; mowing when the grass reaches approximately 6” in height.