I've used part time help twice before. It worked well in one situation and not so well before. The part time worker that worked out good would come in at 3pm and I had a truck and prunning lined up for him. He was trust worthy and would accomplish a good amount of work before stopping for the evening.
Another part time worker I had, would come in after his job at a grocery store. Sometimes he would be late and sometimes he couldn't work (probadly just wanted the evening off). I would always have to meet him at the shop and he couldn't work unsupervised. That was not productive for me.
I need fulltime people who can get a schedule and brief in the morning and go to work all day on a crew of two.