I like the outside the box thinking. I believe most of the 'trade schools' offer some type of property maint/grounds programs already. It seems that you are pushing for more 'hands on' training.
Most of these schools are expensive. Even the local community colleges are pricey and would require one to go into debt. Why go into debt to use a stick edger or hold a shovel all day for 8/hr? I can understand someone wanting to go into debt for electrical work or something similar.
Part of what makes the landscape business so enticing is little to no barriers for entry for both employees and employers.
If someone spends 2 years in school to work as a landscaper, he will be looking for the next best thing while employed by an owner. The turnover will still be high.
Sounds like a great deal for employers, but horrible deal for employees