Here's where to start.

1. Seed Savers Exchange
Members-only non-profit Seed Savers Exchange Yearbook offers more than 12,495 unique varieties to members from members, making it one of the best sources of heirloom seeds in the world. seedsavers.org
2. Thomas Jefferson Center for Historic Plants
At Monticello, Thomas Jefferson created a visionary farm and monument to American agriculture. Their website sells Southern heirloom favorites, such as Carolina Lima beans. monticellocatalog.org
3. Comstock, Ferré & Co.
Established in 1811, in Wethersfield, Connecticut, Comstock, Ferré & Co. is the oldest and likely the prettiest seed store in the U.S. The store’s staff still parcels out the seeds individually and stores them in antique tin-lined oak drawers. comstockferre.com
4. Arcoiris
Arcoiris is the place to find the best range of organic seed varieties from Italy. Their selection of Northern Italian chicories is particularly covetable. arcoiris.it
5. Native Seeds
Indigenous varieties from Northern Mexico and the American Southwest are the focus of these Tucson-based seed savers. Their well-loved catalog is the go-to place for rare varieties of amaranth, chile and corn. nativeseeds.org
6. Irish Seed Savers
These Irish seed activists have compiled an in-depth catalog full of whimsical varieties like the Tipperary turnip and Lucky Leprechaun tomato. irishseedsavers.ie
(Correction: An earlier version of this article referred to seeds sold as “heirloom,” when a more accurate term would have been “open-pollinated.” We regret the error.)