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Don’t want to harsh your buzz, but I have a patch of thyme that’s 6 feet by 3 feet and several years old only 10 feet or so from a plum tree and a rose bush that nevertheless get hammered hard by Japanese beetles every year.
Invest in a sprayer and some neem oil.
This is kind of why I am posting this, I figure thyme will not be enough on its own given how bad japanese beetles get, so am asking for other things I can plant to help control them passively meaning less work for me in the long run, having to constantly spray them is something I am looking to avoid if possible.
Just saw this video where they talk about attracting ground beetles to hunt the japanese beetles. About 7 minutes in https://youtu.be/TIaYP99MKFM
Will definitely do some planting to attract these, I think I'm somewhat out of luck for this year so am gonna have to get scent traps but hopefully plants will be established by next summer and attracting the right bugs to kill off the beetles
Japanese beetles are welcome at my garden. I need a few every year to keep the milky spore active. I put it on my lawn many years ago and only see a handful every year since. Beetle traps are great for increasing Japanese beetle populations - they are attracted to the traps and many fall to the ground and lay their eggs. Japanese beetles also attract moles and skunks.
A nearby town had a mole problem - the moles were eating beetle grubs in lawns - homeowners used poison peanuts to get rid of the moles - boom, BIG skunk invasion.
Milky spore is definitely the way to go for long-term beetle control - I applied it to my yard three years ago and have seen like a 90% reduction in japanese beetles, you just need to be patient since it takes 2-3 seasons to fully establish in the soil.