.. A long time ago there was a channel called The Gardening Channel who did show some of Geoff's progs. but the Channel seems to no longer exist. ...
The Garden Channel still exists, as an organisation. At least someone is still paying for their website to be maintained. Although they are not easy to find on TV. Their website has several hundred short videos on it.
The top level index is here:
You can often find gardening programs on some of the more obscure satellite channels. For example, there was a gardening program broadcast this morning on the Community Channel...
"Garden For Eden. The groundbreaking series presented by Melinda Messenger sees eight amateur garden designers competing for the opportunity to create an exotic eco-garden in the Eden Project."