Pruning Lobelia

Lobelia is an easy-to-grow flowering annual or perennial flower that does not require much in the way of pruning. Many of the more compact flowering annual lobelias are considered self-cleaning and do not require deadheading. Lobelia plants can benefit from deadheading, trimming, or occasional cutbacks to rejuvenate fresh growth in the middle of the season. Perennial lobelias can be cut back to the ground in fall or late winter to prepare for the next season’s growth. Perennial lobelias can also benefit from maintenance pruning and deadheading throughout the growing season to maintain an attractive appearance. 


When to Prune Lobelia

Annual and perennial lobelia do not require any pruning throughout the year but may benefit from maintenance trimming or cutbacks during the growing season. The best time to trim or deadhead annual lobelia is in midsummer to fall as the plant begins to get leggy or lose its structure. The best time to cut back perennial lobelia to the ground is in late fall or late winter. The best time to remove or completely cut back annual lobelia is in fall after the first frost. 


Deadhead annual or perennial lobelia after plants have bloomed and flowers are wilted and browning. Be careful to only trim back the dead blooms and leave new growth or buds intact. Deadhead throughout the growing season when needed. Another good time for maintenance pruning or cutbacks is when lobelia begins to stretch, get leggy, or lose their form. Cutting lobelia back at this time will revive the plant and encourage fresh, new growth. 

Why Prune Lobelia

The main reason to prune lobelia is for general maintenance and overall health and appearance. As the plant grows and blooms throughout the season, the spent flowers should be removed to encourage new growth and new flowers. Beyond deadheading, another reason to prune lobelia is when plants become leggy or overgrown with sagging, open habits. Cutting back lobelia will give the plant an opportunity to rejuvenate. If your lobelia is showing signs of stress from pest or disease pressure, pruning can be beneficial to remove unhealthy portions of the plant. 

How to Prune Lobelia

Step 1 - Deadhead spent flowers 

Trim back stems of spent flowers on an angle

Step 2 - Deadhead as needed 

As flowers die back, remove stems and flowers 

Step 3 - Cut back 

As your lobelia loses its habit, gets leggy, or appears droopy, cut back aggressively to encourage new growth

Lobelia Pruning Tips

  • Do not prune a newly planted lobelia
  • Plan to occasionally deadhead or give maintenance pruning
  • Cut back to the ground to encourage new growth
  • Cut back dead growth at the end of the season

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