Horsetail

The Horsetail breaks the usual sell-for-profit logic, because its value is as a crafting ingredient, not as produce. It is a limited, single-harvest, rare crop obtained from crafting, and crucially it is used to craft Amber Spine and Lingonberry seeds — so its true worth is whatever those downstream seeds are worth to you, not its own sell price.

That reframes the whole economic question. With no listed sell price and only a single harvest, dumping a Horsetail on the market is almost always the wrong move; you would be selling a key that unlocks two other crops for the scrap value of the key itself. The smarter read is to treat each one as reserved inventory for the Amber Spine and Lingonberry recipes.

Because it is single-harvest, every plant is one-and-done, so plan your Horsetail count against exactly how many of those craftable seeds you intend to make. Mutations are largely beside the point here — you are growing a component, not a cash crop. Stockpile it during its limited window so the recipes stay open after it leaves rotation.