Petunias are popular in the garden for their many colors and varieties. They range from large 15-inch-tall plants with 3-inch blooms to diminutive 6-inch, small-flowered varieties that quickly cover bed in their bright flowers. Petunias bloom for most of the summer and into fall. While they can flourish if left alone, they may become leggy and scraggly looking. Trimming them regularly throughout the season and providing a good pruning if they begin to look worse for wear will soon make them lush and vibrant again.
Pinch off the top 1 inch of each stem after transplanting the petunias into their permanent garden bed or container. This causes the stem to branch, leading to a bushier and fuller plant with more blooms.
Deadhead the petunias throughout the blooming season. Pinch off spent flowers ¼ inch beneath the flower on the stem. Pinch off once the petals fade but before the plant sets seeds to encourage more blooms.
Cut back the entire plant using sharp shears if it becomes leggy or ill-kept in appearance. Cut each stem down to half its prior length. For plants that are damaged from storms or look especially bad, cut the entire plant back to within 3 inches of the ground, taking care to leave at least two leaf sets on each stem.
Apply a balanced general fertilizer after severe trimming, following label instructions for application amount. Water well after fertilizing so the petunias will start absorbing the feed and filling back out.