Crocus are a wonderful green roof plant for extensive to intensive green roofs. Bright flowers pop forth in late winter to early spring providing the first signs of the warmer seasons to come. The general rule of thumb when planting crocus bulbs is to cover the top of the bulb with at least three times as much growing media as the bulb is high. This said the smaller the bulb the greater you success on a shallow roof. Crocus are wonderfully low maintenance and love the well drained media of the green roof and will do well in full sun to shade. For the foodie at heart consider planting the saffron fall blooming crocus.