I'm a novice currently working on a whole yard renovation. My yard guy aerated and put down lime, fertilizer, and seed (tall fescue) for me on Sept. 10. I rolled two days later. On Sept 25 I broadcast more seed all over, as germination was sparse. The grass was mainly in the aeration holes in the areas that got some shade. Putting more seed down helped. I mowed some parts last week and put more seed down just in areas that were still mostly bare. Before I did that I wrote to David Hall to get some advice on why I was having problems with germination. He said it was probably a moisture problem. The bare areas got strong sun. And two weeks ago, we had a week of 90 degree sunny days. Although I was watering three times a day, it was drying out between waterings. He suggested a shampoo treatment and also a molasses one. I did the shampoo over the whole yard and did the molasses on certain spots. After that the areas that had dried out quickly stayed damp longer on sunny days. Now to your question about top dressing. On the last seed I put mushroom compost on top, just a very light dusting. The remnants of Karen were to come through and I wanted to keep this new seed from washing. This week we'd had rain about every day (3.5 inches so far) and the grass is finally filling in. In August I had done some shampoo on a hard packed section of dirt where not even weeds would grow and grass from the first seeding grew there. I was surprised at how well it did there. If you have hard dirt, it's worth doing the shampoo. I was happy with the mushroom compost and it did keep the seed in place during the week of rain. In another post you say you're thinking about topdressing before putting seed down. The purpose is to protect the seed. It goes on top, not under. You don't want it very heavy, just a light covering. I just used it in problem spots, not over the whole yard.

thanks for the response Becky.

I have no erosion issues or compaction issues as you had. I was thinking from the perspective of seed to soil contact. I know the dressing goes on top but I would put it down before seeding were I to use it and then gently rake it in to avoid smothering.

Still sounds like the seeds would just be mixed up in the topdressing instead of being directly next to the soil they will be growing in. If I were you, I'd loosen up the existing soil with the rake, put seed down, then put just a very light topdressing on in areas where the seed need some protection. If seed germinates in the middle of topdressing, which is light and soft, what will happen when the root meets the dirt, which is harder? You want it to root in the existing soil, not in the topdressing.You may have a problem now with the calendar. When is frost in your area?

Grass seed must be kept moist so it will germinate. A free standing seed will dry out quickly unless there is some soil (or something) next to it to keep it moist. There are two approaches to keeping seed moist between watering events. One is to either cover it or embed it into a "top dressing." The other is to embed the seed into the soil using a heavy roller. And then both of those approaches must be followed up with watering events, 3x per day, for weeks until the seed germinates.

As to which top dressing is best: If you insist on using top dressing, I'd say you could scratch the surface of your existing soil with a hard rake and seed into that as the best approach. If you don't want to go to that trouble, then compost would be next best. Next best after that would be a ground up mulch material (nothing comes to mind). I would not bring in sand or other top soil material because that will change the profile of your soil and redirect your drainage. The compost and/or mulch will not do that.

When I put the mushroom compost on, I was sprinkling it by hand, using fingertips to apply only a very thin layer. And I was doing it only in specific spots where the seed needed protection. Apparently when people talk about topdressing they mean spreading the material by shovel over the whole area. If that's what you're doing, then it would be too thick overtop seeds and you should instead do what you said you planned to do: seed overtop the topdressing and rake it lightly. Seems to me that it would be better for the rooting to start in the existing soil than in loose topdressing which could blow around or wash. The existing soil is usually not going anywhere and if the grass roots there, it's stable. But if you're not loosening up the existing soil by raking, topdressing would help keep the seed moist.