Petunias are one of the most popular flowers available to the gardener. The reason is that they are easy to grow and be grown almost anywhere and they produce a beautiful and colourful flower. Technically they are a perennial but they are usually treated as an annual and replanted every year. They really only re-bloom in very warm climates.
It is fairly simple to grow petunias from seeds so this is how most people do it although you can get bulbs if you prefer. Ideally the seed is planted in late spring and once the plants are large enough to handle you will want to transfer them to pots. Before planting them outside you will want to harden them by leaving the pots outside for an increasing amount of time each day. Once they reach the point where you can leave them outside all day they can be planted in your garden.
Like most plants petunias like will drained, nutrient rich soil, adding compost is a good way to increase the nutrients in the soil. They should be planted at intervals of about a foot since they do need to have room to spread out. Your petunias need quite a bit of water, more than most other plants in your garden. They also need fertilizer, one that is higher in phosphate than nitrogen. Too much nitrogen and the plant will grow quickly but the flowers won't. Pruning the faded flowers will allow new ones to appear throughout the whole summer.