Gardeners should have to be more qualified than they actually are. Really, it is more difficult to get a job as a gardener than it is to actually qualify for it. Illiteracy—at least in English—is common among even some of the larger and supposedly more reputable landscape maintenance companies. Many who get work as gardeners would have difficulty getting a job doing anything else. It's wonderful for them that they have a crack at such an opportunity, but is it really fair to all of the poor hedges and branches that are going to be shredded and mangled at their hands?
However, education is an asset for upper level jobs. Some landscape maintenance companies want a few educated and experienced members of their staff to make everyone else look good. Besides, larger landscape companies need someone with a "Qualified Applicators License" (QAL) in order to apply pesticides. Qualified irrigation technicians are also needed. Some landscape maintenance companies even like to employ their own arborists who are certified by the International Society of Arboriculture (ISA). These are the people who actually celebrate Arbor Day. Barbecues, party hats, the whole lot.