Our dish was too shallow. Use something at least a few inches deep. If your grass won't grow, spray down the dirt and put some plastic wrap on it and stick it in the oven with the light on inside. Spray it everyday with a misting bottle.
Palm Sunday - Pave the way with cloaks. Sometimes a strong visual makes all the difference in understanding. Try doing this with children - letting them act out the story. Or set this up as a prayer station.