Tulips are unique among common cut flowers because they continue to increase in length significantly even after being harvested and placed in a vase. This consistent elongation sets them apart from most other blooms, which typically cease growth once severed from the root system. The sustained lengthening of the stem, sometimes up to an inch or more per day, often leads to a noticeable change in the flower arrangement. This effect is a genuine biological process that adds a dynamic quality to the flowers.
The Biological Engine Driving Elongation
The lengthening of the tulip stem after cutting is not due to the creation of new cells, but rather the rapid expansion of existing cells. This process, known as cell elongation, is driven by the plant hormone auxin, which remains active within the stem tissue. Auxin makes the cell walls more pliable and receptive to internal pressure, allowing the cells to stretch.
The driving force behind this expansion is turgor pressure, the internal hydrostatic pressure exerted by the fluid contents of the plant cell against its cell wall. Tulips are efficient at absorbing water through their xylem tissue once placed in a vase. The high water uptake provides the necessary internal pressure to inflate the auxin-loosened cells, resulting in the visible elongation of the stem. This continuous supply of water acts as the fuel for the residual hormonal activity within the cut stem.
The most significant growth occurs along the stem section just below the flower head, which is rich in responsive cells. This phenomenon is pronounced; certain cultivars can increase in height by as much as four or six inches during their vase life. This continued growth is a built-in feature that allows the tulip to thrive in the temporary, water-rich environment of a vase.
Caring for Continuously Growing Cut Tulips
Managing the continuous elongation and movement of cut tulips requires considering their unique biological traits. Because the stems will lengthen and move, it is advisable to initially cut the stems shorter than the desired final height when arranging them. This measure accounts for the future upward growth, ensuring the arrangement maintains its intended scale.
Tulips are highly phototropic, meaning they actively bend and curve toward the nearest light source. This bending is caused by an uneven distribution of auxin, which leads to cells on the shaded side of the stem elongating faster than those on the lit side. To mitigate this “dancing” effect, the vase can be rotated daily to encourage the stems to grow straighter.
Due to their high water demand, which fuels the elongation process, tulips should be kept in a vase with a high water level. The water should be changed every few days, and the stem ends should be freshly trimmed at an angle to maintain clear channels for maximum water absorption. Using a tall, supportive vase can help guide the flexible stems and prevent them from drooping as they grow taller and the flower heads become heavier.