You can also use a power rake set to cut about 1/8 inch below the surface. Rototilling is never a good idea to prepare for sod. Within 3 years you will have uneven settling leaving the surface bumpy. Too late now but I've never seen a yard with any St Aug that could not be restored. I do it every few years on my own lawn. One area in my back yard did not get watered enough in 2010. It died and bermuda moved in. In 2011 it was all bermuda. I dropped one piece of St Aug sod in during 2011, nurtured it through 2012, and this spring it is 95% St Aug. You need to know a few things about watering and selective fertilizing to encourage the St Aug, but it can be done.

Yes, you can aerate before verticutting. That would actually help to slice up the soil plugs. The purpose of verticutting is to create shallow slits for the seed to fall into, contact the soil and retain moisture. The slits keep the seed relatively in place, unless you get a real flooding rain. So when you verticut in two directions, you initially get what looks like a grid of grass coming up, but it fills in. I go a little crazy with a verticutter and mow in two directions and then do two directions on the diagonal, but I can get obsessive when I work on a lawn. You can fertilize all at once, after it's all done. That's the fun part. Use a starter fertilizer that contains extra phosphorus for robust root development. Then in mid-November, use a regular lawn fertilizer that is high in nitrogen, a quick release form. The purpose of that last feeding is to get the plants to produce a lot of food resources (sugars) that are then moved into the roots when the plants go dormant for winter. Come springtime, the grass uses those stored foods to emerge from dormancy, thicken up and grow nice and green. There is really nothing you can do to deal with weeds until the grass becomes established, so don't worry about weeds now. Get the turf up and growing. You don't want to do anything to weeds until you have mowed at least twice, but I would wait until next spring to spray. Young grass plants can be vulnerable to lawn weed killers. Also, and this is not fun, if you get a dry winter, you need to keep watering the new grass. It will need about a half inch of moisture every two or three weeks just to stay alive. That probably won't be an issue for you, but down here in KC, I have actually had to hook up hoses and water young turf in the winter. You ask good questions. Don't apologize. And it IS worth doing well, because it's a big job and the seed, fertilizer and equipment rentals are not cheap! Here is a K-State publication on fertilizing lawns. Most if not all of this can apply to SD. Here is a link that might be useful: Fertilizing Kansas Lawns

While you are drinking beer and watching the grass grow, spend some time figuring out the rest of the landscaping. Maybe cut down on lawn area maintenance by having larger areas for shrubs and perennials, veggie gardens and hardscape entertaining areas.

Good job showing us the situation, Ib. That's odd that a moisture-tolerant species occasionally behaves that way, but it does. Here I'm talking about Thuja generally, not GGs in particular. Still, I can't think of any other explanation. Something unlikely, such as a pest-control chemical draining into that area? There's nothing in your narrative to make me think such a thing likely. I do think that once established, GGs would in fact tolerate the moister conditions in that back end, so maybe a gradually rising, raised bed could get you over that hump-and still allow for the single-species effect. I can't think of anything off the top of my head that would both meet your design requirements and be more moisture-tolerant than something from the genus Thuja. Maybe someone else will think of something I'm missing at the moment. +oM