K31 is so drastically different from kbg that I do not think you will get a nice looking lawn with it. I think the thinner-bladed turf type tall fescues may be a better mix or even perennial rye. Core-aerating and then overseeding is a great method. With K31, I don't think you would need to dethatch but the dethatcher may serve as soil prep for areas that do not get cored. If it were me, I would just core aerate the heck out of it.

I did the same thing about 6 years ago, and believe me, you will want to Roundup the K31 prior to reseeding with a TTTF seed. Trying to combine the 2 different types of grass will drive you nuts every time you look at it, not to mention K31 grows so much faster, the blade width is wider, and it grows in a clumpy fashion. They really look like crap together.

The best recommendation I can make is to RU all the K31 you want to replace (if you still have time to do it up there), wait a few days and then mow the existing grass low so yuou can get good seed-soil contact. Then aerate your lawn, reseed, and apply a starter fertilizer. At my HD here I can get Lesco's Turftype tall fescue Transition Blend, which I found to be a very good seed blend (3 different TTTF varieties), or you can get KBG instead of TTTF or combine the both of them. Contact your local hardware stores, garden centers about the availability of the seed and where to get it.

As I said, I don't know it you have enough time to do all of that right now before you get cold weather, but I promise you if you just toss tall fescue seed out over that K31 you will absolutely hate it next year, but each to his own.

OK so maybe I dont want to put in KGB as it wont mix well. I definently am not ready to roundup it yet so any suggestions on what to mix in with myKentucky 31 lawn to make it thicker and softer....? any place online to buy the seed...also what is a good way to put some kind of topdressing on my yard to improve the soil...where do I buy it and what should I use...Im thinking some type of compost material but in bulk type amout as my yard is about an acre
.....Tim

I doubt if there's anything you can do to make it softer and nicer grass if you intend to keep the k31. You can make it thiker by seeding more k31 into it.

HPd195...I think you can aggresively overseed with a KBG / TTTF mix and it will look good after a couple overseedings. I would mow on the shortest level your mower will go and bag the clippings, aerate aggresively (front to back, side side, diagonal - aerate the heck out of it like eriocaulon said), mow again and mulch to break up the cores(this should take care of your topdressing issue because after aerating aggresively you should have soil cores spread all over the surface of your lawn) and then overseed with a mix of KBG/ TTTF.(if you have a mostly sunny lawn) I would then repeat the process next April(don't mow on the lowest setting in April though, just lower) If you do this twice, and aggresively each time, the KBG and TTTF will eventually become the dominant grasses in the lawn..might take a couple years though...and you'll still have some k31 in your lawn.

If you do this, I'm sure you will notice a huge difference in your lawn by next July...if you're motivated, a third time next fall would really do the trick, the only problem is that it starts getting pretty expensive to buy that much seed...AND you better have an irrigation system if you're sitting on 25,000 sq ft, because you have to keep that KBG moist for a month.

I've bought seed online from seedland and seedsuperstore.

One last thing, as the others have said, it might be easier, less expensive, and better in the long run to just round up everything and seed a nice KBG blend...then you only have to do it one time, and the benefit is that you'll have a 100% KBG lawn by next June.

K31 is not a "turf type" tall fescue. It is a forage type fescue. It is about the most hardy cool season grass I know of in draught and heat. Even it will die back though without water and nutrients. When seeded heavily (10-15 pounds per 1000 it does not clump. It responds well to irrigation and fertilizer. If your existing K31 is healthy then overseeding with the same type of grass is usually the best choice when appearance is considered. A turf type tall fescue could also be used. You certainly do not want to try an aggressive elite KBG blend without killing the existing grass. Growth habits are different, fertilizer regimen is different, color is different, water requirements are different - it will be a mess.

Search Lesco. There are several stores in the Cinncinati area that will give you better choices than the box store in seed and fertilizer.

Check with your county extension agent for sources of compost. Your county may have free or low charge. Compost is your best soil improvement.

You really should start at the beginning with a soil test. Find out what the soil needs in terms of fertilizer, nutrients, amendments and then worry about overseeding.