So I would like to know if you keep the items (like seeds, things like weed-b-gone, fertalizers etc) after the Festival is over. I have a seed but I want to save it for next year if its at all possible

Once the festival is over, all the items will be unusable. The following festival may or may not have the same features, using the same/similar items, and even if the festival does run the same way, items from previous festivals will not be counted. The admins may or may not "refund" unused items as a different token that can only be sold back for a few gold.

This is to prevent hoarding of items, causing huge fluctuations of prices between festivals. And also because the admins don't usually plan that far ahead to the next year's festival, as they are always trying to improve the features, but may or may not be able to, depending on what other features they are working on. So they can't guarantee anything for next year's festival.

So if you have anything you want to use, use it by the end of the festival.

Ok, thank you for the information :)