Rare Seed

Sow in fall. Takes all season to grow.
Overview
The Rare Seed is a type of seed that grows into a 

Although its description says that it takes all season to grow, a Rare Seed actually matures in 24 days. Growth time can be reduced with fertilizer that speeds crop growth, and the Agriculturist profession also shortens the time needed.
Because the Seed Maker usually produces an average of two seeds from one Sweet Gem Berry most of the time, Rare Seeds made that way are generally a poor bargain compared to buying them from the Traveling Cart at the maximum available price, even though the cart only offers limited quantities.
- A Livin' Off The Land tip on Fall 1, Year 2 points out that Rare Seeds take 24 days to grow rather than a full 28-day season.
- In Spring and Summer, Rare Seeds can take up two slots in the Traveling Cart's inventory.
Official description
Sow in fall. Takes all season to grow.