A question about tulips and other plants that grow from bulbs: What exactly are bulbs? Tulips grow from bulbs, but does that mean they don’t make seeds?
A bulb is basically a lump of stem with some leaves or at least the bases of leaves — the minimum needed to get a plant started. A bulb enables plants such as tulips and onions to store and protect food beneath the ground in case the plant’s top comes off, which usually happens in winter.
With luck, a plant will produce more than one bulb, allowing for asexual reproduction if the bulbs sprout independently.
The tulip that blooms after a bulb is planted is genetically identical to the original. The bulb is significantly more developed than a seed, so it is much faster to grow a new plant from a bulb. A tulip bulb contains much of the material of the complete plant, including a flower, similar to an embryo in a human or animal.
Tulips make seeds, but they do not produce flowers for five to eight years after they are planted, which accounts for the popularity of bulbs and the near impossibility of finding tulip seeds for sale.
Also, seeds are not genetically identical to the plant that produced them, as they have some DNA from whatever pollinated the plant. This ability to mix genetic material from plants (sexual reproduction) is essential to make new strains of tulips, but there is no way to predict what kind of flower will be produced.
Plants that make bulbs are usually perennials, meaning they come up year after year. As tulips fall into this category, you might wonder why you can’t just plant your bulbs once and be done with it. The answer is they need just the right climate to return, and Massachusetts is not the place for that.
Despite their strong association with the Dutch, tulips were originally cultivated in the Ottoman Empire and like to grow in mountainous areas with temperate climates. You will probably have to replant every year to be sure of having a good garden in the spring.
Ask Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail questions to firstname.lastname@example.org or write to Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.