I will say that part of title one funds is parent education, now you may argue that is not about pto based education BUT if a leader wants to attend a conference about parent involvement without a doubt it will benefit the job they are doing. In cases like that I would say approach your district office to see if they have funds for things like that.
As far as projects like you mentioned I am thinking it would be a tough sell to get any district to openly pay for some one to learn gardening. How about mentoring, are their local places that would volunteer to teach parents some of the things they may need to know.
I can't imagine where you'd go to take a volunteer training class. Normally, the person is expected to have the qualifications they need for the job when they get it.
I am wondering if your pto pays for training of volunteers in head chairpersons, head docent type roles?
I personnally think that if a volunteer is taking on the position of head clay docent, garden committee planner, or technology helper and they are willing to take a special class to better serve the school that the pto should pay for this, similar to teacher training.
Just want to know if any of you do this. It has come up at our meetings, and some think it is fine for teachers, but not for volunteers.