What I like to do to my farm, I place a dirt block 3 blocks above my crops all the way down the line and have torches on every block, this way every plant have light to grow all day and all night. I even place torches next to them to help them grow.
You'll have to place a couple of glowstones(or anything that produces enough light level), or simply expose the crops to direct sunlight.(No other blocks above them.)
please heeeeeeelllp