Why Are My Petunia Blossoms Suddenly Getting Smaller?

Season

• Petunias are summertime annuals and grow only during the frost-free season. In most areas of the country, small blooms in fall indicate falling temperatures and the end of the plants' lifespans. Move the plants indoors or into protected structures for continued growth.

Sun

• The University of Minnesota Extension website notes that lighting is the most important aspect of petunia growth. Petunias do best with six to eight hours of direct sun every day, and they stop producing blooms in shade. Move the petunias to a sunnier location for better blooming.

Soil, Nutrition, Water

• Petunias grow well in loose, nutritious soil and require consistent moisture for growth and blooming. The plants decrease bloom production in poor, water-logged or dry soil. Mix organic compost into petunia soil at planting and again at mid-season to maintain soil quality and moisture. Give petunias balanced 8-8-8, 10-10-10 or 12-12-12 water-soluble plant food once a month to maintain soil nutrients for blooming.

Crowding and Pruning

• Petunias grow and expand quickly and may crowd a site during the season. Crowded petunias restrict their blooming or produce small, weak blossoms. The Clemson Cooperative Extension website recommends pinching off the top half of each planting in this case, to encourage new growth and blooming. Deadhead petunias as the flowers fade to encourage larger, healthier new blooms.