Select a packet of seeds for each greeting card. Use the glue to attach the packet to the front of the card. Don't use a hot glue gun for this, because the heat can damage the seeds inside -- use either a glue stick or regular craft glue.
Use your markers or other craft supplies to write a Spring message inside. You can use something like this if you like:
Wishing you blooms and abundance at Ostara!
orRoses are red, violets are blue,
I picked out these seeds, just for you!
Ostara blessings to you and yours.
Give the cards to friends for the Ostara season.