The USA has tighter regulations for importing seeds than most countries. The only way for an individual to
legally import any seeds into the USA is to apply for an import permit via the
Small Lots of Seed Program at APHIS. The seeds are then sent via an inspection station where they are checked before being forwarded on.
Any seeds sent to the USA without a permit risk being confiscated by customs. The likelihood of then actually being seized is low, but it is a possibility all the same, and whenever I send seeds to the USA I am always worried they will not arrive (but so far they always have done).