Every one I hire is on a 90 day trial basis.
Best saying I ever heard was "Slow to hire, quick to fire".
If he know his stuff $18 an hour is well worth it. He sounds like he is a diamond in the ruff.
Send him here.
I have found Lawn Care is around $12 to $17 an hour and landscaping is around $15 to $20 an hour for good people.
I paid one guy $22 but he went to some one else for $1 more and I would have paid him that for landscaping.