Minecraft – Does an adjacent Grass block affect growing wheat

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).

I'm going to borrow the code for Melon/Pumpkin growing from John's answer to a related question:

int i1 = random.nextInt(4);
int j1 = i;  // Assuming j1 and k1 are the horizontal axes...
int k1 = k;
if(i1 == 0)  // North
{
    j1--;
}
if(i1 == 1) // South
{
    j1++;
}
if(i1 == 2) // East
{
    k1--;
}
if(i1 == 3) // West
{
    k1++; // or somthing like that, anyway.
}
if(world.getBlockId(j1, j, k1) == 0 && world.getBlockId(j1, j - 1, k1) == Block.tilledField.blockID)  // Make sure the targeted block is empty and below it is farmland...
{
    world.setBlockWithNotify(j1, j, k1, field_35297_a.blockID); // Place a melon.
}

This code works by first picking a direction, then checking if it is farmland, and then placing a melon/pumpkin if it is. Therefore you will get higher yield if there are more farmland blocks around the vine, as if you only have 1 there is only a 1/4 chance of this function creating a melon/pumpkin when it is triggered.