Keep Petunias And Calibrachoa Shining All Season

By: Jessie Keith

Petunias in Pastel Bathtub Container

Petunias look good planted almost anywhere or in anything.

For glowing garden color nothing beats that old standby, the Petunia. Why? Petunias, and the closely related Calibrachoa, are tough, pretty and thrive in containers and sunny flower beds. And, for designing with annual color there’s no better choice; happy plants bloom nonstop and come in a broad array of exciting colors — from blue to magenta and even green! The only drawback is how they dwindle in mid- to late-summer if not properly maintained.

Petunias On the Cusp of Need

Petunia Phantom and Petunia Black Velvet on the cusp of need. Click on the image to enlarge.

After an early- to mid-season explosion of color, they start to look worn and peter out as the dog days of summer hit — especially container-grown plants. But, you can stop this floral decline before it begins. A few simple steps will ensure top petunia performance well into autumn.

STEP 1: Start Right

First, start big and plant right. For best success, purchase starts as larger vigorous plants in three to four-inch pots, rather than small, needy plugs or meager seed-grown specimens. This will provide you with more vigorous, prettier plants faster.

Next, be particular about amendments or container medium. If your planting beds need a boost, amend with Black Gold® Earthworm Castings or Garden Compost. Both will fortify soil and yield bigger, happier bedding plants. Containers should be filled with a light potting mix that is porous, yet moist enough to be easily irrigated. Black Gold® Natural and Organic Potting Soil Plus Fertilizer is a top notch choice. (Bagged mixes of lesser quality are heavily pre-wetted, harder to handle and offer less aeration.) Increase the water holding capacity of any medium by adding a three to one ratio of Just Coir.

Petunia Integrifolia - Jessie Keith

Petunia integrifolia always benefits from a midseason trim and feed.

Choosing the right fertilizer is essential. High phosphorus fertilizer specialized to promote blooming and rooting encourages faster root development for healthier plants and more flowers. Choose an OMRI Listed fertilizer approved for organic gardening. For best results, fertilize containers every five to six weeks.

It is generally stated that petunias and Calibrachoa need full sun for best blooming, but they will flower nearly as well in partial sun, especially where summers are very hot and humid. Overall, six hours of direct sunlight will suffice. Any less will yield plants that are leggy and flower poorly.

STEP 2: Maintain, Prune, Maintain!

Pruning Petunias - 2up

Continue to prune back leggy stems. The end product may have a clipped look but never fear; in a few weeks they’ll be in full bloom again.

Consistent care and a midseason pruning are essential to keeping petunias blooming vigorously up to frost. Regular water is crucial — especially for container specimens. Just one day of water missed can dry up a plant and leave it looking poor for weeks until nurtured back to health. During hot, dry spells twice daily watering may even be needed. Before watering, check by feeling the soil to the depth of two inches—if it feels barely moist to dry, it’s time to water again.

Supertunia Royal Magenta, Salvia Leucantha and Lantana Camara - Jessie Keith

This fall garden bed with Supertunia Royal Magenta, Salvia leucantha and Lantana camara shows how beautifully petunias shine late in the season.

Petunias need a midseason chop to bounce back to their early summer glory (ground cover petunias, like those in the WaveTM series, are an exception). Cut them back considerably by ¾ in mid-July to keep them from developing old, bloomless, leggy stems. Unlike petunias, Calibrachoa don’t require midseason pruning unless they begin to look ungainly and then only a light trim is required. Follow up by giving pruned plants a boost of fertilizer, a good drink, and within a couple of weeks they will burst forth again in glorious bloom.

Enjoy Into Fall

When it’s time to plant potted mums, asters, ornamental peppers and colorful kales, I always work them in and around pre-existing petunia and Calibrachoa plantings. Nothing’s prettier than a raspberry red and pink Supertunia® Raspberry Blast petunia weaving itself among fall standards like steely ‘Winterbor’ kale and ivory mums. Beautiful!

Here are some more examples of all the different and beautiful shades and hues available when you plant petunias and Calibrachoa this season!
Petunia Supertunia® Royal Magenta - Jessie Keith

Petunia Supertunia® Royal Magenta


Calibrachoa - Superbells - Chiffon Yellow - Jessie Keith

Calibrachoa, such as Superbells Chiffon Yellow, require little to no pruning unlike most petunias.


Petunia 'Fame Salmon Pink' - Jessie Keith

Petunia ‘Fame Salmon Pink’


Large-flowered Grandiflora Petunias- Jessie Keith

Large-flowered grandiflora petunias are the most needy when it comes to pruning.

About Jessie Keith

Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.