Alex, for info, my younger works for the national trust as an assistant head gardner and loves it. He qualified as a building surveyor with a very good degree but never practiced as his sandwich year experiences put him off.
He then won a place on the Trust's careership programme which is a 3 year qualification that accepts about 15 people nationwide every year. It's salaried during training too.
He's been doing it for about 8 years now and is going for head gardener positions which, when you consider mostly come with accomodation, aren't badly paid at all. And the locations are usually rural, so the money goes further.
He's very fulfilled by what he does, is mostly self sufficient as he's got a small allotment producing year round fruit and veg which feeds him well, and has a wonderfully healthy lifestyle.
As FRH above says, it's more than gardening, as he researches, plans, manages teams of staff and volunteers as well as getting stuck into plenty of manual work creating and maintaining the gardens. It's physical and cerebral.
He could earn alot more in private practice, but designing concrete gazebos and water features for the Chelsea set just isn't him.
I'm full of admiration for the guy and wish I had the courage to do something similar.
I'd recommend you at least consider it as you seem to already have had a taster and liked it.
He's back from sabatical in NZ next week, so PM me if you want to talk to him about it.
Col.