neighbor's planter crosses the property line

State: California

Part 1: We recently moved into a new home and I have discovered that the next door neighbors had built a planter that crosses property line by about 2 feet. Apparently, the neighbors discussed this with the previous homeowners and the previous homeowners told them that it was ok to do this.

Part 2: The same neighbor has been cutting, fertilizing, and generally maintaining the grass that is on the side of the driveway where the planter is. I have told him it is not necessary, but he continues to do it.

My question is, are we at any risk of losing ownership of the areas that he has been maintaining? Is there any law in California that relates to the issue of someone losing ownership of their property if someone else has been maintaining it for x amount of time?

Thank you -

[HomeGuru]

Yes, so search posts under search words adverse possession.