Sacha wrote in
:

It might be possible to do it as a side line and perhaps to specialise
in e.g. Herbs or something. But nurseries are NOT a way to get rich
and in fact, nor are garden centres it seems now.

The OP mentioned 'garden centre' in his title, but his post suggests that
he really just wants to start selling things he has propagated himself.

Mail order might be a possibility? I don't know about garden stuff
specifically, but Ebay traders can make a decent living, if not a
fortune?

Either is likely to be lower-risk than setting up in face to face retail,
which as Sacha suggests, needs a fair bit of initial investment, and
would probably involve expensive and fiddly things like hiring staff.

Anyone starting up a business which they expect to do more than provide
pocket money, should talk to:
a lawyer,
an accountant who knows a bit about personal tax and small businesses
Business Link
any local Enterprise type organisation.

(they will probably contradict one another, but it's handy to note the
points of disagreement!)

Tip: lawyers and accountants are used to everyone they meet being bored
or irritated by what they do. If you already know one, try looking
flatteringly interested and they can be tempted to hand out extremely
useful free advice & anecdotes. Beer helps.

There are grants around for all sorts of mad things these days. If you
can bear the paperwork, there's surprising amounts of cash swishing about
for some things: check for publically funded bodies in your area/market
who can point you in the right direction.

Victoria