No idea the laws or standard practices in OP’s location but a general rule of thumb where I am is if you flipped the house upside down anything that falls to the ground goes and everything else stays-meaning anything that’s attached/affixed to the property stays (or at least should be specifically referenced in a contract as included or excluded with the rent/sale). Plants that have been planted into the ground could be reasonably expected to stay from the new renter’s perspective, they have no way of knowing that was an improvement made by the current tenant and not the landlord/owner. The landlord messed up by not having this discussion explicitly with the current tenant and just assuming they were leaving the plants. I think it would be reasonable for the new tenant to require the landlord to plant a new garden to match the old, especially if it was specifically advertised that way