How do I grow tall Glowing Mushrooms?

Solution 1:

I set up two mushroom gardens to test this:

One: -200 feet, torches every few steps under the one block of mud, about 4 mushroom grass planted at the same time.

Two: -800 feet two mushroom grass planted at the same time, one with a torch underneath, one with no torch.

Result: In garden one the tall mushrooms grew all over the place at about the same time. In garden two the tall mushroom grew under the torchless portion first.

Conclusion: torches don't really matter, just be at negative depth, give about 20-25 blocks of space above. Above all, wait. The tall mushrooms take a while to show up.