Journey North Tulip Garden and Climate Change Study

What's Happening Underground?
Bulb Life Cycles

— Teacher Background —

Are bulbs completely dormant and lifeless underground, or is something actually going on? Read on to learn a bit about bulb life cycles:

Fall - Winter
Each fall, we plant spring-flowering bulbs that are in their dormant (resting) stage. When the underground temperature drops below about 50 degrees F, each bulb begins to form roots again in preparation for blooming in the spring. You can see these if you dig up a bulb during this period. The cold also triggers cells that will begin to make new leaves and flower buds in preparation for spring. Although you can't see this, this period of at least 9 weeks of temperatures below 50 degrees is necessary for the plant to bloom again. (In warmer climates, people artificially simulate winter by keeping bulbs in the refrigerator or another cool place for 9 weeks. People also use this strategy to "force" bulbs to bloom indoors. See Hurrying Spring.)

Spring:
Spring warmth and rains trigger the bulb to begin to grow rapidly, pushing up the shoots, leaves, and flower bud. Finally, the bud bursts into bloom.

Late Spring - Summer:
Most people will walk right past a bed of green-leaved tulips after they have bloomed and ignore them. Little do they know that this is a really important time in the life of this little bulb plant. The leaves continue to grow and make food for the plant. New bulblets form next to the original bulb and start to grow.*

During the summer, the leaves die back, the roots dry up, and the food is stored in the dormant (resting) bulb and bulblets. In the fall, the cycle begins again.

*Making New Bulbs:
A bulb propagates itself asexually by growing small bulblets attached to the original bulb. It can take a year or more before bulblets are big enough to produce blooms. Because these grow right from the parent plant, they produce the exact same flower type and color.

Bulbs also produce seed, but they can take up to six years to produce a flower this way — and the new plant isn't likely to look like the parent. Plant breeders often cross-pollinate two types of bulbs to produce seeds of a brand new variety.