Greenhouse

7x7 farmland with a water source block

the buff will appear inside a finished greenhouse

A greenhouse is a structure intended to make farming crops possible in colder climates or for multiple harvests into autumn or winter. If built correctly, the farmland inside of the structure will show an additional line for the effect of "+5°C". Which means that crops growing inside of the structure on these farmland blocks will be 5°C warmer than those outside at all times.

Requirements

The following building requirements must be met to designate a building as a greenhouse:

• A greenhouse structure can have a maximum inner size of 7x7x7 blocks. Smaller sizes in all dimensions are possible, but never more than 7 blocks in any one dimension. Only the direct walls count, the corner rows can be left out without affecting the room recognition.
• The roof needs to be at least 50% transparent material (glass, quartz glass, coloured glass or even glacier ice) with a direct open line to the sky. There cannot be any other blocks between the greenhouse roof and the sky, meaning greenhouses are impossible underground, even if there are sufficient light sources. The roof can be made from slabs or full blocks, and it does not need to be flat. In version 1.18.0, lower slab blocks also qualify for roofing pieces (though curved roofs have not yet been tested).
  • The "solid" face, the face of the slab block that lines up with a full block, must be facing inside for it to count as a roof.
• The ground must be built from full blocks, path blocks, or farmland. Ensure that there are full blocks under each farmland or path block.
• The walls can be slabs or full blocks of any kind. Several greenhouses can share the same walls. Slabs can be oriented both outward or inward. The whole greenhouse could be lowered into the ground completely to leave the roof on ground level as well, as dirt and stone are both accepted block types for the walls. However, the player should ensure to not be too far below sea level, incurring the underground farming effect.
• You can put a water source block in the greenhouse, but be sure to have a full block beneath it. To save room, it is possible to hide the water source under the outer walls.
• Chiseled blocks are fine in the walls/roof so long as they don't have big holes that lead outside.
• While normal doors or trapdoors are fine even when not closed, rough doors prevent a room from being recognized as a greenhouse and should therefore not be used.

Protip: It might take a little bit of time before the +5°C buff appears on the farmland blocks inside of the structure, and not all blocks will be updated simultaneously. To be precise, every farmland block checks for a greenhouse after a maximum of 4 ingame hours - plus minus a few seconds - and will check in every direction for walls & roof stopping the search in the allowed distance of up to 7 blocks.