Petunias are popular annual bedding plants, prized for their long-lasting color in garden beds and containers. They produce a large number of tiny seeds, giving them the natural ability to self-sow into the garden environment. While petunias can reseed themselves, the resulting plants, often called volunteers, may look drastically different from their parent plant. The success and appearance of these new petunias depend heavily on the original plant’s genetic makeup and environmental factors.
The Crucial Difference: Hybrid Versus Open-Pollinated Varieties
The primary factor determining a petunia’s reseeding outcome is whether it is a hybrid or an open-pollinated variety. Most modern petunias sold in nurseries are F1 Hybrids, resulting from a controlled cross between two distinct parent lines. These hybrids are bred for desirable traits such as unique colors, disease resistance, and vigorous growth, which are uniform in the first generation (F1).
When an F1 Hybrid petunia produces seeds, those seeds belong to the second generation (F2). Plants grown from F2 seeds do not breed true to the parent, meaning they will not reliably replicate the F1 plant’s characteristics. Instead, the F2 generation often exhibits a genetic reversion, displaying traits from its less-showy “grandparent” plants. This frequently results in smaller flowers and less vibrant colors, often reverting to shades of pink or purple.
In contrast, open-pollinated varieties, often called heirloom or old-fashioned petunias, possess a stable genetic structure. Their seeds are produced through natural pollination within the same variety and consistently yield offspring that closely resemble the parent plant. Gardeners seeking predictable reseeding outcomes should seek out these open-pollinated varieties, as they ensure the new plants maintain the original flower size and color.
Maximizing Natural Reseeding Success
To encourage petunias to self-sow, gardeners must stop deadheading, which is the removal of spent flowers. Allowing faded blooms to remain permits the development of seed pods, which are small, round structures at the base of the flower. The seeds inside the pod are ready for dispersal once the pod dries out, turns brown, and cracks open.
The successful germination of these tiny seeds depends heavily on specific garden conditions. Petunia seeds require light to germinate, so they must land on the soil surface and not be buried. Garden beds should have minimal or no mulch where the plants grew. The soil should also be lightly disturbed to create good seed-to-soil contact.
Germination typically occurs in late spring or early summer once soil temperatures consistently warm up and the risk of frost has passed. The soil must be kept consistently moist during this period, but not waterlogged, as the seeds are delicate and susceptible to rot. A mild winter climate also increases the likelihood of seed survival and subsequent sprouting.
Identifying and Managing Volunteer Seedlings
The appearance of new petunia seedlings, or “volunteers,” usually occurs in late spring, often in unexpected locations. Distinguishing small petunia seedlings from common weeds requires careful observation of the first set of true leaves. These leaves will have a distinct shape and texture compared to weed sprouts. These volunteers often appear densely clustered beneath the location of the previous year’s parent plant.
Once the seedlings have developed a few sets of true leaves, they should be managed to ensure adequate growth. If they are growing too closely together, thinning is necessary to provide space for air circulation and nutrient access. Thinning involves carefully removing the weakest seedlings. The remaining plants should be spaced approximately 6 to 12 inches apart.
Alternatively, the young plants can be carefully transplanted to a new location in the garden or into containers. Transplanting is best done on an overcast day or in the late afternoon to minimize stress on the delicate root systems. Despite the unpredictable nature of hybrid volunteers, allowing them to grow can result in interesting and unique color combinations.