can you mail seeds to usa

I would check with Customs and excise. I know some places are a bit funny about seeds etc being taken or sent abroad,
Or check with an American Embassy.
It may sound silly with this advise but at least you can cover yourself and not get in trouble yourself

The American recipient will first have to obtain a 'licence' to import the seeds. A copy of this will have to be included with the seeds. When the seeds get to America they will be subject to scrutiny which can take a couple of months.
The SRGC sends seeds to Americam members every year. There is no difficulty from the UK end but our American friends can get get very impatient.

Below is the advice given to American members by the Scottish Rock garden Club. It includes the web site for further information.
Hope this helps, Koniejane.

Seed Exchange Notice for USA Members
In 2006 the US authorities introduced new regulations regarding the import of seeds into the US, which apply to all US residents requiring seed from the Seed Exchange. To participate in the SRGC Seed Exchange, our US members must have a 'Small Lots of Seeds' permit, which is issued by APHIS. We advise that you get the permit now, rather than wait until the seed list arrives. You can find details of how to get a permit at: http://www.aphis.usda.gov/import_export/plants/plant_imports/smalllots_seed.shtml
We must emphasise that it has to be a 'small lots' permit, as this is the only permit which does not require phytosanitary certification at our end.
When you send your seed order, we need a copy of the permit, the conditions attached to it and a green and yellow customs label for that permit for each of your orders - one for a main order, and one for each order of 50 packets in the surplus.
Please read all Seed Exchange instructions