by Robert Pavlis
This is common advice and works in most cases, but there is more to the story.
Although this advice is popular, it is hardly ever explained. Is the planting depth measured to the top or bottom of the bulb? The rule would be much clearer if it was worded something like this, dig the hole two or three times as deep as the height of the bulb. The depth is measured from the bottom of the bulb.
This is a general rule that does not apply to all bulbs. Some like to be deeper, and others like to be shallower. Soil type also affects planting depth. In heavy clay that stays very wet, it is probably better to plant higher. Most bulbs want to be dry in summer, and some rot very easily if they are too wet.
Climate is also a factor. Cold-sensitive bulbs will do better if they are planted deeper, and some say that you can cheat the hardiness zone a bit if you plant deep. I am not sure this is true; it could be another myth, but it is warmer at deeper levels.
Many bulbs have a mind of their own, figuratively speaking. They will move up or down to a level that suits them. I always find that daffodils go deeper than where I plant them, and grape hyacinths move up so they are just below the surface of the soil. In zone 5, you can just throw grape hyacinth on top of the soil, and they will slowly bury themselves over a couple of years.
Written by Robert Pavlis, author of three books, , Garden Myths , Soil Science for Gardeners and Building Natural Ponds. Have a question for Robert – connect on his Facebook Group: Garden Fundamentals