St Augustine spreds via stolens, so should be easier to control (that if it had rhizomes also). Stolens are on top of the soil. A simple barrier will keep back the St. Augustine.

Zoysia is slow growing and tougher to mow. It is also subject to thatch buildup, and you need to use caution when dethatching becase that will slow it’s growth also. Zoysia spreads by means of slow growing underground rhizomes and above ground stolens. These rhizomes will tend to go under barriers. Your lawn will over take his lawn eventually, unless you have a ‘root barrier’. Watering should be to 6″ deep at least – to establish deep roots, for a healthier lawn, so you should have a root barrier of 8″ or more.

Do consider an Integrated Pest Management practice, this will save you lots of money (pest being bugs, fungus, weeds…). The Clemson Master Gardeners class presentation on Turfgrass has a section on IPM and on Zoysia grass too.

PS – the metal barriers will rust away also, consider HDPE 30 mil. I can only find 15″ depth or more. When using this to stop Bamboo rhizomes, 24″ is recommended. It cuts fairly easy – so you could take a roll and cut it to size. A ditch witch rented for a day will make the needed trench – I know this is a lot – but in the end, you will be sure his stays put, and he does not get your’s.

I also think your Zoysia is the more aggressive species, so it is your neighbor who should be worried. Do you live where Winter is an issue? I am pretty sure Zoysia turns a very odd light brown in Fall, at least in Massachusetts.

hmmmmmmmmmmmmmmmmmmmmm.

how stupid are people