Terraria 1.4 introduced a new type of seed called Gemcorn. They can be planted to grow Gemtrees, which will then yield some stone, Gemcorns, and Gems when they are harvested.
Gemcorns are a little odd in that they need to be planted on a stone in the Underground layer or below. The less light there is, the faster they grow, so the ideal circumstances to plant them in is actually total darkness. It can take up to an hour for the Gemtrees to grow, but it could take longer depending on how much light there is.
You can make a Gemcorn by combining an Acorn and a Gem at a workbench. Gemcorns can be made in the following variants, and you will need the right Gem to make them:
The type of Gem you use will dictate the type of Gemcorn you get and the resulting tree type. If you are fortunate, you will come across some Gemtrees in caverns while you are exploring, but they appear to have a very low spawn rate, so making the Gemcorns yourself is arguably the best route to take.
Players are reporting various yield values for the trees, but it would appear that you can expect to get up to 20 blocks, 5 Gemcorns, and 4 Gems when they are harvested, so making your own Gemcorns and growing them into Gemtrees is certainly worth the effort.
That’s it for Gemcorns and Gemtrees, but if we learn any more secrets about them, we will be sure to update this guide.