Petunias x hybrida is an annual, lasting only one growing season, and is United States Department of Agriculture's (USDA) hardy in zones 2 to 8. Petunias have fragrant, funnel-shaped flowers in a variety of colors. The Wave petunia grows horizontally and cascades from planter boxes and containers. Petunias prefer full sun and well-drained soil. You can buy petunia plants, or start your own from seed.
Petunia seeds are extremely small--about 250,000 seeds per ounce. This makes growing petunias from seeds challenging for even more experienced gardeners. These small seeds are difficult to handle. Commercial seed suppliers now sell pelleted petunia seed. This means the seed is covered with a special coating. This increases the size of the seeds and makes them easier to plant. Seeds can be purchased in small packets or in bulk. Although the coated ones are more expensive, they are easier to handle and germinate faster.
Planting Seeds Indoors
As with most plants, you can start petunia seeds indoors while there is still the danger of frost outside. This will give the plants a head start and they will be further along when it is time to plant. The seeds should be started 10 to 12 weeks before that last potential frost. Seeding requires a good germination medium for the seeds to grow. A commercial potting soil works well. They also require seed starter trays with holes in the bottoms for good drainage. Petunia seeds need light, moderate temperatures and moisture for the most favorable germinating conditions.
Transplanting petunia seedlings requires several steps based on the size of the seedling. Once they have germinated and have at least two leaves, they can be moved from the seed trays to individual containers. This is usually around 14 to 21 days after planting. At this size, you can start to fertilize them and slowly acclimate them to the move outside.
Sowing Seed Outdoors
Seeds can be planted directly outdoors after the danger of the last frost has passed. The soil should be prepared and amended with organic mulch or compost and tilled before seeds are planted to ensure proper germination.
Once outside, petunias are easy to care for and are relatively disease- and pest-free. They prefer full sun and are heat tolerant. They require water and fertilizer although some species require more than others. Wave petunias requires more water than other varieties. Encourage more blooms by pinching or deadheading regularly.