Keeping ants off potted lemon tree

re-pot the tree in the next size up with fresh soil,spray the leaves with horticultural oil

I have read cornmeal keeps ants away.

Borax is a natural and repellent. If you mixed some with water and sprayed just the leaves, the ants may disappear. You MUST avoid getting any on the fruit, as borax is toxic if ingested

I just sprinkle cleanser around the bottom of the pot, ants don't cross over it.

https://www.hometalk.com/diy/outdoor/pest-repeller/cheap-easy-homemade-ant-spray-31195184

packaged cornbread mix that says it is sweetened and put it where they are. They will take it to the mound, everyone will eat it and die, they can't digest the cornmeal, but will take it because it is sweetened. Little goes a long way.