Gemcorns

A gemcorn is an Acorn combined with a gem, and planting one is a one way transaction. Once it is in the ground you cannot pull it back out; breaking the sapling returns nothing at all. So the real question is not how gem trees work but whether the tree gives back more than the Diamond or Ruby you buried to make it.

Gemcorns go on Stone Blocks below the surface layer, and biome and mossy stone variants all count. The block beside the one you plant on has to be stone as well. Beyond that:

• No liquid in the lower tile of the sapling or in the two tiles either side of it.
• No background wall behind the lower tile, unless it is one of the grass, jungle, flower or fence walls that plants tolerate.
• Vertical clearance of 11 to 16 tiles, measured as a five tile wide column centered on the sapling with nothing in it but other saplings. Less headroom within that range means a slower, shorter tree rather than no tree.
• Three tiles between saplings, so branches from one do not sit in the growth space of the next.

Light is irrelevant. A gem tree in total darkness grows exactly as fast as one under a row of torches.

Left alone a gem tree takes something like 32 in-game hours on average, which is a long wait in real time unless you are sleeping through it. Fertilizer matures one instantly provided every condition above is already met.

Infused Fertilizer is a trap here. It wants 26 to 31 tiles of clearance, roughly double what the tree itself needs, so in a farm built to the normal 16 tile ceiling it will not work anywhere. Either build the whole room tall enough for it or do not stock it for this.

Averaged over many trees, one gem tree returns about 1.5 gems, 20 stone and 2.1 gemcorns. Every tile of the tree rolls a one in ten chance of dropping a gem and otherwise gives a block or two of stone, and each leafy branch has a coin flip to return a gemcorn. Barren branches, the ones drawn in flat gray with no gems visible on them, return nothing extra.

Two conclusions follow. The farm is self sustaining, because it hands back roughly twice the gemcorns it consumed, so you can replant and bank the surplus forever off one initial batch. But it is a trickle, not a mine. The variance per tree is enormous and plenty of individual trees give back no gems and no gemcorns whatsoever. If you want gems this afternoon, go dig; if you want a slow passive supply running in the background of a long world, plant a wall of these and forget about them.

Dig a long horizontal room in the cavern layer, floor it with stone, and mark planting spots every three tiles. Hammering the stone in between is a neat trick: a hammered block will not accept a gemcorn, so the spacing enforces itself and you stop losing gemcorns to a misplaced click.

Wall the whole thing with fences. They satisfy the plant growth exception while still counting as wall coverage, so nothing spawns in the farm and you can walk it unarmed. Avoid mossy stone even though it is legal, because the moss fuzz grows into the clearance and blocks the sapling, and once a tree has grown on a mossy block you can no longer scrape the moss off it.

Label the rows. A gem tree is hard to read from a distance and harder in the dark. Colored torches or gemspark blocks under each planting spot work well. Illuminant Coating on the trees themselves is better, since it makes the gems on the branches visible with no light at all. Paint is the option to skip: painting the floor block paints the tree that grows from it, which is the one thing that makes the gem color harder to identify.

Extra gemcorns are worth exactly what their gem is worth, so they sell fine as they are. Better, drop them in Shimmer to split them back into acorns and gems: the gems sell, and the acorns go into your next batch or into a wood farm. In a Skyblock world the calculation flips completely and stone becomes the point, since the trees drop it directly and gem money buys anvils you can shimmer down into more of it.