Minecraft PE. Grass not growing?

Ok so I have minecraft pe on my iPhone and I have a map that is COMPLETLY water except for one little island. So I put brick ontop of the water and built things ontop of the brick. But I left one little corner of the map water, then I decided to build a little island there out of dirt, hoping it would grow grass, but it didn't. It's been days, and not one of the dirt blocks has grown into grass. I don't know if it effects anything but the "island" is floating, if you dig down a few blocks then you'll hit water. So it's not connected to the actually ground. I would really like grass to grown on this island but I don't know how to make it grow!

I think that grass can't grow on dirt that is directly on water:/ or make sure the dirt its exposed to the sun that always works if none of these works then you'll have to create another map:/

For the grass to grow on dirt blocks you need one dirt block that has grass connected to it. Just make sort of a dirt bridge from some block that has grass to your island and the grass will make its way there.