If you can get hold of it on DVD then “The Victorian Kitchen” garden series with Harry Dodson, Peter Thoday and Ruth Mott is not only the best gardening TV show I’ve ever seen, but also my most favourite programme ever. Literally the most informative programme, while also being amusing and light. A must see for any gardener- the series “Victorian Flower Garden” and “War time kitchen and garden” are part of the same series and are on YouTube, but Kitchen Garden is the best one.
Otherwise Gardener’s World is ok, and YouTube for programmes featuring Christopher Lloyd and Rosemary Verey - their Desert Island Discs appearances are also on BBC Sounds - they’re superb.