I came across this old thread because we are adjusting the contour of our Zoysia grass lawn And I wanted to check the recommendations for barrier depth. it turns out our old barrier is only 4” deep and it has easily contained the rhizomes from spreading underneath. What we have to watch is those that want to grow over the barrier. That’s just a matter of edging the lawn regularly. Nevertheless, I am installing a 6” deep barrier this time only because we have tree root problems going everywhere, but I think 4” is plenty deep. I’ve had this zoysia grass lawn for at least 30 years and never regretted choosing it. I chose it because I had German Shepherd Dogs and I wanted a grass that would take ball chasing and peeing. If I didn’t wet the urine spots down when they happened, the grass would tend to die out. But zoysia sends out rhizomes to cover those bare spots rather quickly. It also stands up well to big dogs chasing balls. It is extremely drought tolerant. It is thick and luscious underfoot. and while it does go straw colored dormant in winter, it does not go dormant for long, especially in the warmer winters we’ve been experiencing the last few years. Last winter it didn’t even go fully dormant. To compare, I’ve grown buffalo grass and it has a MUCH longer period of dormancy and is no more drought tolerant and not half as attractive. One more thing, I have a seedless cultivar of Zoysia so there is no seeding about. It’s a great lawn Grass.

Some of those grasses don't coexist very well. Are you sure it is centipede and not St Augustine? Centipede has sharp looking blade tips while St Augustine has blunt tips. Centipede is also easily shaded out by just about anything. If what you have is St Augustine, then you can reclaim your entire lawn with just proper care and no herbicides. It can smother just about any grass. It has trouble with a few broadleaf weeds, but knowing that in advance can save you from letting them get ahead of you. I'm not big on zoysia lawns. The biggest problem is they often will not recover from damage in the same season the damage occurs. There are a couple lawns in my neighborhood that got a disease following 15 inches of rain all falling in June. Those diseased spots are barren still today. They will not recover until next April when the grass comes out of normal winter dormancy. Whereas with St Augustine you can recover easily in the same season. Or if you are interested in a seeded bermuda lawn, it can be nice, but they require monthly fertilizer and mowing 2x per week to really look good. For that you would have to get rid of the other grass or it will look weedy. No matter what you do, I hope you realize that daily watering is only for establishing new seed or sod. Once the lawn is established only monthly (cool weather) or weekly (hot weather) watering is needed. If you are watering daily now, that might be your problem.

Image is still on the market as far as I know. Image is for nut grass and other bulb-originating weeds (like wild garlic/onion). I purchased Image at Home Depot. What weeds are you trying to kill? Always read the label of any herbicide to make sure it is safe for your grass (helpful for others to know even if you already know that). Here is a link that might be useful: Image

You will need to become a label reader! There are many such herbicides on the market. What you are looking for is: SELECTIVE, POST-EMERGENT, GRASS HERBICIDE. These products can be sprayed over broadleaf ornamentals and garden plants and will control the grasses and grassy weeds. The monocots. Poast is such an herbicide, but there are many name brands.