Hop Seeds are on sale at Herm’s from his second tier, but you cannot plant them in a garden bed. Hops need a Vine Trellis, which comes with the vineyard technologies, and that is also what stands between you and brewing your own Beer.
Unlike the other seeds, they do not press into Seed oil either. Until the trellis, all you can do with them is study them: 1 Science for 20 green.