• A sunflower displaying its enormous headsunflower image by Lucid_Exposure from Fotolia.com
  
  The wide open spaces of parks, lawns, public and private gardens are frequently home to large shrubs and plants bearing larger-than-average flowers that can cover more ground with fewer plants. Once firmly established, they usually don't require much attention past occasional fertilizing and, in some cases, separating clumps of newly-propagated bulbs.
  
  

Sunflower

• American Giant, Skyscraper and Mammoth sunflowers, are some of the biggest flower-producing plants, in height as well as in flower head diameter, featuring flowers up to 3 feet in diameter on stalks up to 20 feet high. Amazingly, these monstrosities are easily grown from seeds.
  
  

Star of Persia

• The Star of Persia, a member of the Allium family, displays purple-to-lavender, flower-clustered heads that grow 10 to 12 inches in diameter. These slightly onion-scented, edible plants grow from bulbs and originated in Iran.
  
  

Passion Flower

• The Passion Flower has varieties that produce blossoms up to 6 inches across, grow in sun or partial shade, and require very little care once they are established. Passion flowers provide the total life-support of three types of butterflies: zebra, Julia and gulf fritillary. Its vine features air tendrils that cling to wood, stone, or bark as it progresses up trellises, arbors, trees or fences.
  
  

Magnolia

• The Magnolia tree, a native of eastern North America, Central America, West Indies and parts of Asia, exhibits 3-to-12-inch white, pink or purple flowers and belongs to a family of plants called Magnoliaceae.
  
  

Hydrangea

• Pink, blue, and white hydrangea flowers from hybrid cultivars mature into large blossoming clusters, reaching 12 inches in diameter.
  
  

Dahlias

• Some varieties of dahlias, native to Mexico, form dinner-plate size blossoms exceeding 10 inches in diameter. Because of the weight and size of these flowers, growers must limit the number of flowers to around 4 per stalk.
  
  

Clematis

• The clematis vine flaunts showy purple, red or white blossoms that grow from 5 to 7 inches in diameter. The vine blooms from July to October.
  
  

Hibiscus

• Hibiscus has cultivars that produce flowers up to 12 inches in diameter. The grandiflora varieties thrive in bogs and marshes. Although these flowers bloom year round in southern Florida, they bloom best during the cooler months of fall through early summer.