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Why Petunias stop blooming

Could be the weather or management practices

By: Sandy Feather ©2015
Penn State Extension


Q. Our petunias were blooming their heads off until mid-August, but they have just about stopped blooming. How do you get them to rebloom, or are they finished for the season?

A. Petunias do look great for the first few months, but it is common for them to slow down in hot, humid weather. They do not bloom as well, and may become bare in the center of the plant(s). They just look...tired. There are some standard management practices that can help prolong petunias’ bloom period.


Petunias not blooming

Extending Petunia Blooming:

• Deadheading is the removal of spent blooms, including the ovary (the swollen portion just behind the flower). This prevents the plant from producing seed. Many annual flowers slow their flower production when they put too much energy into seed production, and petunias really benefit from this practice. This should be done frequently through the growing season to encourage continuous bloom.

petunia basket

• Petunias are heavy feeders. It is helpful to fertilize petunias (and most annuals) regularly during the growing the season, especially when they are grown in containers. Since containers have to be watered frequently, the nutrients are leached out of them quickly.

 

If you plant your own pots, incorporate a coated release fertilizer such as Osmocote or Schultz MultiCote Time Release Plant Food into the soil mix according to label directions. Remember that more is never better when it comes to fertilizer because it can burn plants to death if it is over-applied. If you purchase pre-planted containers, you can topdress with the same type of fertilizer. Then follow up with a water soluble fertilizer such as Peters 20-20-20, Miracle Gro or fish emulsion every other week through the growing season.


pink petunias

Now that your plant has set so many seeds, it is hard to say if it can be rejuvenated. If you want to try, cut back about a third of the leggy stems to five inches or so. When they respond with a flush of growth, cut back the second third. When those show signs of growth, cut back the final third. If you cut the entire plant back so hard all at once, it would probably die. By spreading the stress out and allowing it to recover in between, such hard pruning rejuvenates rather than killing. When you start this process, use a water soluble fertilizer at quarter strength every time you water.

wave petunias

Finally, when you are buying petunias next year, look for some of the newer varieties. Plant breeders feel your pain and are releasing some of the longest blooming, most carefree petunias that gardeners have ever had the pleasure of growing. These include the Madness Series, the Wave Series, the Cascadias Series, and the Supertunia Series, as well as others. Petunias are a much-beloved annual flower in the United States and gardeners are finally getting the petunias they deserve.

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