From today's ResearchBuzz.com newletter -
There is a new online service, locatetv.com, that allows you to search by topic, actor, episode name and other criteria.
Locatetv provides extra information that you may not have had. For example a search for the topic "gardening" led to the show called "Gardening by the Yard" and the date of production, 1995.
Below that is a list of upcoming episodes, the channel and time. When you click on an episode it shows the original date. Saturday's show, "Fall Chores" is a 2006 program. Etc.
Botanical gardens such as Missouri Botanical Garden are included in museums that have podcasts. Look at Museumpods.com for places you might want to go over the holidays.
At Surfmind.com you can search for "botanical" and get great links, including. botanical gardens, herbals, master gardeners - well, look for yourself or use your own search terms to find what interests you.