If you're only inviting one plant into your garden beds this spring, it's likely to be a petunia. Petunias (Petunia spp.) are easy-care, flowering beauties usually grown as annuals and discarded at the end of the season. Many are, in fact, herbaceous perennials that thrive in U.S. Department of Agriculture plant hardiness zones 9 through 10.
Petunia foliage turning yellow is never a good sign. It usually indicates a problem with the way you are caring for the plants, from nutrient deficiencies to too little sun.
Good Cultural Care Essential
You plant petunias to brighten up your garden with their deep-purple or pink showy blossoms and brilliant green leaves. Whether you are growing grandiflora or multiflora varieties, you will not be happy to see your flowers' foliage turn yellow.
The best way to avoid yellowing foliage is to start with excellent cultural practices. Given that most petunias are grown for one season only, serious diseases do not have time to develop. Any yellowing of the foliage is usually due to the way the gardener is caring for the petunias. For example, all of the following can cause petunia leaves to turn yellow: planting too deep, planting in shade, planting in poorly draining soil and failing to provide fertilizer.
Caring for Petunias
Petunias don't ask for much in exchange for making your garden lovely. They require full, direct sun -- at least six hours a day -- and light, well-draining soil. If you get significant wind in your area, pick a planting site with some shelter. Transplant the petunias at the same depth they were growing before transplant because deep planting can yellow the foliage.
Be sure to check the roots before you plant because tightly wrapped petunia roots won't get sufficient nutrients. Untwist the roots before planting and trim them if necessary. If you do, soak the garden pruner in an mixture of equal amounts of water and denatured alcohol to sterilize the tool.
Petunias need regular irrigation, so give them enough water to keep the soil moist but not wet at all times. It is best to water them by soaker hose before the sun rises in the morning so they don't burn and water doesn't get on their leaves. They also need fertilizer. Apply a water-soluble general fertilizer every 10 to 14 days. One tablespoon of fertilizer mixed into a gallon of water will feed plants in a 10-square-foot garden bed.
Petunias and Tobacco
Smoking or using tobacco produces can be bad for you; this is no surprise. But did you know they can also be bad for petunias?
If someone using tobacco products touches your petunia plants, it can spread tobacco mosaic virus to them. This virus turns the foliage a mottled yellow and deforms the leaves as well as the blossoms. Protect petunias and keep all tobacco products out of the garden.