Petunias come in several beautiful varieties and are relatively easy to grow and care for. Flower blooms for different petunia varieties range from mini petunia flowers less than 1 inch in diameter up to the more popular grandiflora petunia bloom which is between 3 to 5 inches in size. Just as with any other type of flower plant, proper spacing of the plants plays an important part in determining whether a petunia planting will be a failure or success. Space requirements for petunias will generally depend upon the variety that is being planted.
When planting grandiflora petunias, how much space to give them will depend on where the flowers are planted. If you live in cold or moderate temperature climate zones, you should space your grandiflora petunias about 12 inches to 15 inches apart if planted in direct sunlight areas, and plant them about 8 to 10 inches apart if planting them in shaded areas. In order to avoid weeds from strangling grandiflora petunias, you can space the petunias closer together - if they will be transplanted relatively soon. Allowing grandiflora petunias to mature too close to each other will usually result in less blooms and flowers because of the larger size of the blooms and the plants having to compete for moisture and nutrients in the soil.
Spacing for multiflora petunias can be a little more forgiving, but should not be ignored. While you can usually plant multiflora petunias a little closer together than you could with the larger grandiflora variety, multiflora varieties also should not be crowded or allowed to grow into each other. Many people choose multiflora varieties because they are much more prolific bloomers; however, placing the plants too close to each other will inhibit new blooms and flowers on most varieties. Keep spacing for multiflora petunias between 6 to 12 inches in the sun and 5 to 9 inches in shaded areas.
Spreading petunia varieties such as the wave petunia need plenty of space in order to grow laterally. Some varieties of spreading petunias can grow up to as wide as 4 feet or so, and you should space your spreading petunias up accordingly. You can help increase the height of some varieties of spreading petunias by planting them about 2 1/2 feet apart. However, this will require some frequent pruning to keep them from growing into each other too much.
Hybrid Variety Petunias
Today, hybrid petunias are a very popular option for many home flowerbeds and gardens. Many varieties of hybrid petunias give you the larger, more striking flowers of grandiflora varieties as well as the weather resistance and tolerance of smaller multiflora petunias. Spacing requirements for hybrid petunias vary considerably by variety; so, you should ask a knowledgeable staff member at your local garden nursery about spacing requirements for the type of hybrid petunia you are thinking of planting. If you are unable to easily obtain this information, you should follow the same rule of thumb for grandiflora or multiflora varieties. Plant larger varieties a little farther apart, and place smaller varieties a little closer together.