From the USDA APHIS website (
https://www.aphis.usda.gov/aphis/resources/traveler/intl-travel/plants-seeds/plants-seeds):
Travelers may bring seeds of admissible herbaceous plants for planting if they meet the following conditions:
- The seeds are not otherwise prohibited, protected under the Endangered Species Act or Convention on International Trade in Endangered Species of Wild Fauna and Flora, or subject to any special restrictions, such as post-entry quarantine or treatment*
- You have a phytosanitary certificate issued by the National Plant Protection Organization of the country you are leaving indicating the seeds are free of pests and diseases
- U.S. Customs and Border Protection inspects the seeds at the first port of entry and determines they are free of pests and diseases and meet all entry requirements
*Please call APHIS’ Plant Import Information Line at 877-770-5990 (toll-free) or by email at plantproducts.permits@aphis.usda.gov.
Some information on USDA websites indicates that tree and shrub seeds can be brought back to the US per requirements listed above, yet some sources say none can be brought back with passenger luggage. Best course of action would be to shoot an email inquiry to that listed email.