Whether you deadhead Lobelia depends heavily on the specific type you are growing. Deadheading, the removal of spent flowers, is generally recommended to encourage a longer, more vigorous bloom period. This targeted maintenance technique varies significantly between common annual bedding varieties and taller perennial types. Understanding these forms, such as the mounding annual Lobelia erinus and the upright perennial Lobelia cardinalis, is the first step in effective care.
Why Deadheading is Essential for Lobelia
Deadheading manipulates the plant’s reproductive cycle. When a flower fades and remains on the stem, the plant directs its energy toward producing seeds. By removing the spent flower, you trick the plant into bypassing the seed-setting phase. This shifts energy back into vegetative growth, stimulating the production of new flower buds.
This results in a prolonged and more abundant second flush of blooms, keeping the plant fresh and colorful throughout the growing season. Removing faded flowers also improves the plant’s aesthetic quality by eliminating unsightly foliage.
Techniques Specific to Different Lobelia Varieties
The method of deadheading is entirely dependent on the physical structure of the Lobelia variety. Annual Lobelia erinus, often used in hanging baskets and as edging, produces masses of tiny flowers, making the removal of individual spent blooms impractical. When they begin to look straggly or their blooming slows, the appropriate technique is “shearing” or “pinching back.” This involves cutting the entire plant back by approximately one-third to one-half of its height using clean shears to stimulate a fresh burst of growth.
In contrast, perennial varieties like Lobelia cardinalis and Lobelia siphilitica have a different growth habit. These plants produce tall, distinct flower spikes that bloom progressively from the bottom to the top. For these types, selective deadheading is performed by snipping the individual flower spike back to a set of healthy leaves or to the base of the plant once the entire spike is finished blooming. This method encourages the development of new side-shoots that may produce additional flowers.
Timing and Supporting Plant Health
The correct timing for deadheading or shearing is when the plant’s flowering begins to wane, typically around mid-summer as temperatures rise. This mid-season cutback gives the plant enough time to recover and produce a second bloom before the first frost. For annuals, continue this shearing practice until the plant naturally declines in the autumn.
Perennial varieties require a different seasonal approach; cease active deadheading in late summer or early fall. Stopping allows the plant to form seed heads and direct its energy into developing a strong crown and winterizing foliage. This is necessary for the plant to survive the winter and return the following spring.
Since deadheading or shearing expends significant energy, provide immediate nutritional support afterward. Following a heavy cutback, apply a balanced liquid fertilizer to fuel the next cycle of blooms. Adequate watering is also necessary immediately following the trim to support the rapid development of new stems and flowers.