Question
Ken, I'm planning to aerate and overseed this weekend (1 year old fescue lawn zone 6 with hard clay ground. I'm planning to do the following:

1.Mow grass 1-2 inches
2.Lay down granulated gypsum (to help soften ground?)
3.Aerate
4.Run a slit-seeder
5.Lay starter fertilizer
6.Lay granular lime if needed pending lab analysis
7.Wait 4-6 weeks and winterize (28-3-14)

The ground is rock hard. Do you agree with slit-seeding after aerating or would you just recommend spreading seed after aerating? Also, what is the recommended amount of seed and fertilizer per square feet? Thanks for your input.  

Answer
You can aerate and slit seed. The advantage of slit seeding is that the seeds are placed in good soil/seed contact which is recommended. If you are just talking about a dethatcher (vertical mower) then that is fine, too. It will not deposit the seeds, but it will open pores in the soil, preparring for seeds.

I would skip the gypsum unless you know for sure that the sodium levels in your soil is high. Gypsum only works on sodium rich clay soils. Also, it is most effective if you till substantial quantities into the soil (a small amount layered is not going to do much).

If you are looking to improve soil quality then try to top dress the clay soil with compost after core aerating. it is a big process and can be expensive. I would probably skip it all together.

If you use regular commercially available lawn fertilizer, such as Scott's Turfbuilder or Bayer Advanced Lawn Fertilizers then use 3 lbs per 1000 sq feet lawn fertilizer.

Use 3-5 lbs of grass seeds per 1000 sq feet for overseeding.

Remember to keep the soil damp at all times until the seeds sprout.

Since you will be watering frequently, I would rake the cores before seeding. Otherwise cores tend to mash down and smother seeds and grass (clay cores can do that).