1) A seed pouch. All seeds go directly to this pouch. The whole pouch can take up a single inventory spot.
It can be won either from achieving a certain rank of gardening, or from a special gardening quest. Just PLEASE don't make it able to be bought from the crowns store!
2) Seeds stack. Seeds only take up an inventory spot for each different types of seed.
i.e. If you have 3 Pink Dandelions, a White Laugh-O-Dil, and 2 Burning Snap Dragons, they take up a total of 3 spaces. This would be a passive effect that does not need to be unlocked.
Feel free to comment on these ideas and offer any suggestions or feedback!
Hunter Fireshield 86
I like the idea but there is already something like this called the "Seed Vault", it works a little different when it comes to storing things but it gets the job done. It is also fairly easy to craft and the recipe is sold by Toshio.