Because tulips are not just edible, they are YUMMY, here in the land of chipmunks, squirrels, and voles, I plant my tulips 10 to 12" deep (and yes, they will come up). This serves to protect them from digging critters (and voles don't generally tunnel that far down) as well as protecting somewhat from our hot humid summers which they really don't like. Because they are so deep, I cover them with soil, then when I'm at a six inch depth, I plant daffodil bulbs right on top of the tulips, cover the daffs until the noses are no longer visible and place crocus bulbs right there. Then to finish it off right, top with pansies...Voila, a bouquet....