Spring is the best time to plant tender bulbs like dahlias and caladium. Fall is the best time to plant hardy bulbs like irises and tulips. Plant tender bulbs 6-12 inches apart and hardy bulbs 3-6 inches apart. You should dig the hole 2-3 times the depth of the bulb height. If you bury bulbs any deeper, then it will either bloom late or won’t bloom at all. Put the bulb in the hole you’ve dug nose up and root down. Click here to read more.