Petunias produce an abundance of gorgeous blooms from early spring until a frosty fall day finishes their growing season. Keeping petunias in bloom mode is simply a matter of pruning and regular deadheading to encourage more growth. Pruning can also help keep the plant somewhat compact, making it look more lush as it produces more stems and flowers.
Deadheading Every Week
Deadheading petunias is a bit different than deadheading some other flower varieties. The goal while removing dead petunia flowers is to also remove seeds that develop below the flower. Check the plant every week or so for wilted flowers. Pinch the stem to break it off 1/4 inch below the spent flower or the seed pod. If you prefer to use a tool, sharp, clean pruning shears work well. For both deadheading and pruning, sanitize tool blades first with rubbing alcohol or an inexpensive alcohol-based hand sanitizer.
Since a number of blooms may be on the same stem, it may be easier to wait until a full cluster of blooms has wilted or died before deadheading them. To deadhead a cluster of flowers, pinch off or snip the stem to just above a flower that is still blooming or about to bloom.
Deadheading petunias encourages new flower growth. Some varieties, such as the massive grandiflora petunia, must be deadheaded to keep the plant blooming profusely throughout the growing season.
- Note: Some petunia varieties such as Wave and super petunia don't produce seeds, so it isn't necessary to deadhead them. The blooms will fall off on their own. If unsure of the variety, check the plant marker or tag, or ask the grower if your petunia variety produces seeds. Although deadheading is not necessary, these plants can still be deadheaded if you prefer not to see wilted flowers on your plants.
How to Prune Petunias
How you prune petunias varies a bit depending upon the variety; for instance, a spreading or wave petunia is supposed to develop long, cascading stems, requiring little pruning or maintenance. It's normal for cascading or trailing varieties to develop long stems, as these petunias are designed to spread out over a landscape or spill over the sides of a hanging basket or planter. On the other hand, if a mounding petunia or variety such as a grandiflora develops long, spindly stems and starts looking unkempt, it's time for a trim.
When stems become too leggy or overgrown on just about any variety of petunia, including cascading or trailing types, they may produce fewer flowers. Prune several inches off the tops of leggy stems, or even cut them to half their length, using your favorite sharp hand-pruning shears. This encourages new, more compact growth. Snip leggy stems to an area just above leaf growth, new stem offshoots or buds. Sanitize the shears first to help prevent plant diseases.
Mid-summer is the best time to do an intensive pruning, as there's still plenty of growing season left for new blooms. Cutting them back encourages a more compact shape, with energy focused on flower production. Water the plant thoroughly after any major pruning. Feel free to do minor maintenance pruning on the plant at any time once it is well established.
When Blooms Slow Down
If the petunia isn't producing nearly as many blooms as it used to and there's still plenty of growing season left, a drastic pruning may be in order. Remove 2/3 of the stem length on various under-producing stems around the plant, but this aggressive pruning should be performed on no more than one-third of the stems at a time. Repeat the process on additional stems after waiting a week or so, then one more time in another week. It could take a month for new blooms to appear on the previously pruned stems. The plant will also produce more stem and leaf growth, making it appear fuller.
If the growing season is already winding down, feel free to cut back 2/3 of each stem on the entire plant, keeping in mind that it still takes up to a month for new bloom production. Cutting back old stems late in the season encourages lots of branching and intense flower growth for an impressive show of color.
With any type of pruning, make sure some leaf growth remains on the intact stems.
Kathy Adams is an award-winning writer. She is an avid DIYer that is equally at home repurposing random objects into new, useful creations as she is at supporting community gardening efforts and writing about healthy alternatives to household chemicals. She's written numerous DIY articles for paint and decor companies, as well as for Black + Decker, Hunker, SFGate, Landlordology and others.