I'd find someone else too. After all you don't really owe him anything, if he's not doing the job properly then it stands to reason.
I think by the sounds of it he doesn't want to do your garden for some reason and he would probably be relieved.
Carry on with new guy and if he approaches you just explain you thought he might now be too busy etc. so you've employed someone else.
Change the name in a tv show /movie title to the above user username
Vickram Digra's sentence increased rather than decreased.
Any thoughts on what happened to Henry?……
