Generally OK: Heirloom and open-pollinated varieties without restrictive labels, patents, or licenses; varieties whose Plant Variety Protection has expired (20 years, or 25 years for trees and vines); and seeds pledged under the Open Source Seed Initiative (OSSI).
Do not share: Seeds labeled “Unauthorized Propagation Prohibited”, “Unauthorized Seed Multiplication Prohibited”, or “U.S. Protected Variety”; seeds with patent numbers or license terms; or protected varieties, even as a free gift. The law covers transfers, not only sales.
Heads up: Open-pollinated and F1 hybrid varieties can both be protected. Check the variety name. Saving protected seed to replant in your own garden is generally allowed; giving it to others is not.
How to check: Search the variety name at the USDA PVP certificate search ↗ or GRIN PVP status search ↗.
Sharer responsibility: People who post or share seeds are fully responsible for their own actions and for ensuring the seeds can legally be shared. Veggios Seed Exchange and Three Green, LLC are not responsible or accountable in any way for the illegal sharing of protected seeds by users.
This is general information, not legal advice.