What's the best way to grow mushrooms?

The best pattern of mushrooms to make to grow them optimally

1. Flat ground. Mushroom spawning is 50% likely to happen at the same height, or 25% likely higher or lower by one block. If it can't be spawned there, then the chance is wasted.
2. Sparse planting. Mushrooms spread as far as two blocks away, so make enough room for them.

The rate of growth is only affected by the above two factors.

Other conditions that affect growth

If you can plant it by hand somewhere, it can be spawned there. No other factors. I.e.

1. Only at empty space (air blocks) with light level <= 12;
2. Only on opaque blocks.

The rate of growth at this optimal layout

Well, I can't predict exactly. But it should always be much slower than other plants' (it seems 100 times slower but i'm not sure).

Setup

1. Make a 13 long × 9 high × 4 high room.

2. Divide in four quarters, digging down along the short edge and up along:

   ABCDEFGHIJKLM   (Top down view)
   ▓▓▓▓▓▓█▓▓▓▓▓▓ 1
   ▓▓▓▓▓▓█▓▓▓▓▓▓ 2        ↑
   ▓▓▓▓▓▓█▓▓▓▓▓▓ 3 Higher ░ - Head room
   ▓▓▓▓▓▓█▓▓▓▓▓▓ 4        ▒ - Room Floor
   ▒▒▒▒▒▒▒▒▒▒▒▒▒ 5        ▓ - Growth area
   ▓▓▓▓▓▓█▓▓▓▓▓▓ 6 Lower  █ - Collection area
   ▓▓▓▓▓▓█▓▓▓▓▓▓ 7        ↓
   ▓▓▓▓▓▓█▓▓▓▓▓▓ 8
   ▓▓▓▓▓▓█▓▓▓▓▓▓ 9
   

3. Decide where you want the mushrooms placed (the video skips every other row and column) and place trapdoors immediately above.

4. In all other places, except for the very center and the corners, place half-slabs (mobs can't spawn there.)

   ABCDEFGHIJKLM   (░ and ▒ layers)
   #^:^:^:^:^:^# 1
   ............. 2        . - Half slab 
   .^:^:^:^:^:^: 3        : - Three half slabs
   ...........:~ 4        ^ - Trapdoor
   ......#....:. 5        ~ - Water source
   ...........:~ 6        █ - Collection area
   .^:^:^:^:^:^: 7        # - Nothing
   :..:...:.:.:. 8
   #^:^:^:^:^:^# 9
   

5. In the center area, place a pressure plate in the center and a ladder for vertical access

Planting

6. Plant mushrooms through trap doors

7. Remove lights.

Collecting

1. Place some torches.

2. Place water sources in the corners, collecting from block M5

3. Go through the opening in the middle

4. Fight off the spiders that will have spawned and collect the mushrooms in there.

I saw building two floors is easier one brown floor the other red . Causes more mushrooms to spawn by giving them more room. I have two floors each 11x17 height of 2 so you can walk around. When planting scatter then beacuse they grow in a X shape. Also it's best to just farm them on peaceful so you can remove all lighting which causes them to grow faster. Once collected and mushroom soup is made put it on normal or whatever. My rooms usually within an ingame week I.e a couple of hours. Hope this was helpful.