How do I build an efficient underground farm?

Solution 1:

I have the following underground farm. It's not optimal in terms of space, but for a farm, it's very efficient, and has automatic harvesting. Planting is always manual on these things unfortunately, and that's the bottleneck for massive production.

TOP VIEW

SSSSSSS
DDDDDDD
DDDDDDD
DDDDDDD
DDDDDDD
SXSSSSX

I replicate the above pattern, one level up to the right for as long as you want. S is stone. D is tilled dirt. The trick is with the X blocks. They are water blocks at the level of the dirt blocks covered with Stone.

LEFT VIEW

S    S
SDDDDW

When you view this from the left, you see there's a channel for water to flow out of your monitor. That is what permits automatic harvesting. The water blocks are necessary for hydrating the soil.

On the far right, I place a water gate.

Solution 2:

I have a 3 level underground farm, i'll post picks of it later on tonight, its about 7x24 and 4 tall for the first 2 levels and the 3rd level is my cocoa tree semi auto farm the first 2 levels are copies of one another in layout, The layout is as follows

7 wide by 24 long grid

WddsddW

WddsddW

WddsddW

WddsddW

WddsddW

And just continue that till its 24 blocks long W is water D is dirt S is stone Place torches along the wall at your discretion. The cocoa farm is too complicated to describe on here, but youtube is a good place to look up ideas. Ill take pics and make a video of it shortly if you like the layout

Solution 3:

Not mechanized but very efficient both in means of space, effort building, effort harvesting and planting.

Water must be at most 4 blocks away (Manhattan taxi metrics), and more doesn't improve growth. Light improves growth, and placed above won't take room occupied by wheat. This much light will keep monsters from spawning too.

The basic unit of your farm is going to be a 9x9 square. There is one-block hole filled with water in the middle.

 ........
 ........
 ........
 ........
 ....~...
 ........
 ........
 ........
 ........

Then, above the soil place glowstone. You might put a solid layer of it, but a pattern of 1 every 4 blocks reduces the efficiency only marginally.

 ...G...G
 .G...G..
 ...G...G
 .G...G..
 ...G~..G
 .G...G..
 ...G...G
 .G...G..
 ...G...G

Crossection would be like this:

#-stone G-glowstone |-wheat =-farmland ~-water

#########
G G G G G

|||||||||
====~====
#########

Repeat that 9x9 pattern in line, as many times as needed. Instead of just running ahead, "reaper motions" (turning around while holding the button) harvest up to 4 lines away at a time, so harvest is fast enough that you really don't need automation. And digging is just 9x9x4 or even x3 if floor is soil.