No I need to replace a free gardener?

Maintenance

Hi
I have been providing a free gardener to current tenants as there is a large garden. The gardener refuses to return whilst these tenants are present due to many issues. I am not willing to pay more for another gardener (he was charging less than going rate.)
Contract states tenants are responsible for garden, but so far they haven't been.

Can I tell them to look after the garden per contract?

Do I legally need to provide them with lawn mower, tools etc?

Should I lower rent, even though they have never paid for the gardener and it is their behaviour which has caused this gardener to quit?

Thanks for your thoughts.