Petunias are a long-standing favorite annual of gardeners all over. An easy-to-grow self-seeder that is tolerant of some shade but shines in full sun, petunias are a great plant for the beginner to master.
Petunias are best bought in six-packs from garden centers; they are available in shades of red, pink, white and purple with trumpetlike blooms. Petunia seeds are very small and cumbersome to grow. While an annual, petunias will often return each year as a self-seeder in conditions where the ground does not freeze over hard.
Cut a sample of soil by digging straight down about 2 inches, and place the sample in a container. Try to stay away from areas of your garden where leaves have decomposed or where you have recently fertilized. Take the sample to your local extension office or full-service garden center for pH testing. Petunias, like many annuals, prefer a balanced nutrient soil, so the test will show you what you need to add for the right nutrients.
Plant 12 inches apart or closer in semishady areas after the threat of frost has passed. Crowd petunias growing in containers or window boxes closely together for the best effect.
Pull blooms off of new plants gently. By removing blooms, you are forcing the plant to spend energy on plant growth instead of blooming. It sounds counterintuitive, but in just a couple of weeks, you'll have many more blooms and a stronger plant than if you allowed it to start blooming as a seedling.
Water and fertilize regularly. Petunias growing in containers may need watering more than once a day in extremely warm temperatures. Make sure pots have drainage holes, because wet roots are susceptible to rot.
Deadhead spent blooms as they begin to wilt. Dropping dead flowers and producing seeds are extremely energy-zapping for annuals, so if you remove dying flowers before the plant starts to seed, which is its goal, it will continue to force more and more blooms to get to the seeding stage.
Prune back leggy or long, stringy-looking stems in midsummer if you feel they are unsightly. This will cause the flower to grow more shoots which will result in more blooms.