Okay, thanks for the answers to the questions. Here's the deal with St Aug and bermuda in the same lawn. IF YOU WATER IT ENOUGH, the St Augustine will take over. IF YOU DON'T, the bermuda will take over. Once you let it get dry enough that the St Aug dies, you're done for with the St Aug. Bermuda will go dormant with no water while St Aug dies and will never return without new grass. So you have to make up your mind to water back there. Once you do that, the existing St Aug will fill in for you and choke out everything else. Now I say 'everything' but there are some broadleafed weeds that will force out the SA, but usually the SA takes over when it's watered.
Don't ever mow low if you want St Aug. Weld your mower adjusters in the highest position so you can't make the mistake of lowering it. If you want St Aug there is NEVER a reason to lower it. The only reason to lower it is to get seeds to sprout. Since St Aug doesn't grow from seeds, the only seeds that might sprout would be considered weeds. Therefore you never need to lower your deck.
Since you're going to resod anyway, here's a plan for that. Rent a mower and scalp your lawn to the dirt. The reason you want to rent a mower is that you will ruin the blade doing this. Chew up everything and mulch it. Try to keep from gouging any deep ruts but do cut it to the ground. Water that chewed up grass to the point of being soggy. Immediately lay your sod right down on top of the wet chewed up grass. Then use a water fulled roller to roll the sod down to make good contact with the soggy stuff under there. Roots will not grow into open air so you must roll the sod. Then, that same day, apply corn meal to the turf at 10-20 pounds per 1,000 square feet to take care of any fungus disease the grass might have been left susceptable to from the sod farm. Then water from the top for an hour a day, all at once, for three days. Then start to back off watering every other day for a week. Then you can probably back off to weekly watering for an hour at a time. If the grass ever changes color to blue-green or seems dry, water it.
If you really want to do it right, between the pieces of sod you could pour in a 50/50 mix of sand and compost. If you can keep the pieces of sod touching, you really should not need this.
There's no reason to till your soil. In fact there's lots of reasons not to till. Rather than go into them all without knowing why you might want to till, can you tell me if that was just something you though you should do or did you have a reason to till?
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