Some people are lucky, because they know exactly what their ancestors grew in their gardens. Others are still tending plants of their forebears, especially in the form of vineyards and orchards. Most of us have to do a little more digging just to get an idea of what our ancestors grew, but luckily, there are numerous sources of information.
Ideally, we want to know what individual ancestors grew, but this can be difficult to find, so we may have to find general sources, and then extrapolate from there. However, your ancestor could be mentioned in a source without your knowledge. Here are some possibilities:
Family History Compilations
Aside from asking family members, many family history compilations can be found at libraries, particularly local ones in the area of your ancestors. They often contain nuggets of information that you cannot find in online databases. Someone from a previous generation may have known or heard stories about an ancestor, and they may have documented something like, "Uncle Webb grew the best Muscadines." If Uncle Webb happens to be your ancestor, and you have a general idea where he lived, you can corroborate info from other sources, such as data from the Census and Death Certificates, and you may find his street address. Your search may turn up photographs of family members standing near the vines or other gardens. Perhaps one day you can visit the address, and maybe even find those Muscadine vines!
However, it's up to you as to whether or not you want to take clippings for yourself, with permission, of course. As for me, I am still reluctant to take any vine cuttings, because Uncle Webb was not only someone's uncle, but he was my great-great grandfather. As much as I would love to grow something from his property, I have been exposed to a lot of articles and webinars about the dangers of bringing potentially diseased (and insect-infested) vines into the vineyard. However, if you can find the same variety of plant from a facility selling certified material, then go for it!
Newspapers
More old newspapers are appearing on the internet, but you may not find the ones you want online. Some online databases are free, while others require a subscription. Some state governments, particularly the state archives, may offer free historic newspapers online, too. Again, you could always visit the local library in your ancestor's region. You can search for your ancestor's name, if the source includes a search function. Some people were actively involved in local gardening clubs, particularly in the early-mid 1900's. Another lucky find would be discovering your ancestor won a County Fair for something like the Best Blueberry Pie! Even if they did not grow blueberries, you'll get an idea of what they probably liked to eat!
If you cannot locate any names in the newspaper, then you can scan the advertisements to get an idea of the kind of produce and flowers being grown in that region. You may have to make a more general search, and then use some deductive reasoning to determine what was popular in their area, rather than finding out exactly what they grew.
Antique Books
By now, most people are aware of archive.org, a fantastic resource for finding online books from historic eras. You can search for books by general topics, although it may take some time to find the right keyword combination. Whether or not the book is online, you can find some really interesting details about what was grown in a given area. You may even find a name you recognize, such as a neighbor mentioned alongside your ancestor's Census record, or perhaps even your own ancestor! I'm still waiting for this to happen to me!
University Archives
Another source of antique books can be the archive room of a local university, particularly one with an agricultural heritage. My alma mater, North Carolina State University, has an incredible library. It would be easy to get lost amongst the stacks of information, whether or not you are in the Agricultural or Engineering Department. I spent a little time in the Fashion Textile section, because I needed an escape from my own studies! I just wish I could have explored their Agricultural section in-depth. Most states have at least one good Agricultural School, and they may have that one little tidbit of info you seek, but you may have to set aside many hours to search. Before embarking on a trip, see if the school has an online catalog, so you can get an idea of what records to request.
History Museums
You may want to look up any history museums in the region of your ancestors, especially those with heritage gardens, like the one in Colonial Williamsburg in Virginia. A quick glance at the Events Calendar may reveal an upcoming Field Day where you can ask museum staff and volunteers about the specific plant varieties. Another example of such a place is Red Hill, the home of Patrick Henry. Attendees may be lucky enough to catch the museum's Boxwood Sale, where they sell containers of potted clippings from boxwoods grown on the property for many years.
Heirloom Seed Catalogs
It's easy to get lost looking at photo-shopped images of fruits and vegetables, but some heirloom seed catalogs give details about their seed sources, so it's a good idea to scan the descriptions. It may not be the exact variety of what your ancestors grew, but you may find what was grown in their hometown. Also, some botanical societies have annual plant sales, and they are often passionate about sharing the history of their offerings, particularly societies devoted to antique roses and heirloom irises. You may not find the names of your ancestors, but you may find some pretty flowers grown during their era!
Overall, just have fun with the search. Or, you could just bypass all this, and buy wine and food products from the region of your ancestors. I tried to do this when I discovered there is an award-winning cheese in Québec known as Zacharie Cloutier, made by Fromagerie Nouvelle-France. He happens to be my ancestor, as well as the progenitor of many others in Québec. According to a university study, Zacharie Cloutier was the Québec colonist with the highest number of descendants by the year 1800. Expect to hear more about him in the Floramont Journal. However, let me stay on-topic and wish you lots of luck with discovering the roots of your own heritage! Bonne Chance! Translation: Good luck!