Globe Amaranth, or Gomphrena, is a popular ornamental annual prized for its globe-shaped, clover-like flowers that hold their color long after being cut. Gardeners often wonder if this vibrant, long-blooming flower will reliably return to the garden on its own through self-seeding. Self-seeding is the plant’s natural ability to drop mature seeds that germinate and grow new plants the following season. While this can happen with Gomphrena, it is far from guaranteed, as success depends heavily on specific environmental and biological factors.
The Conditions for Self-Seeding Success
Gomphrena self-seeding is highly dependent on favorable conditions, making it unreliable in many temperate climates. As a tender annual, it requires a long, warm growing season for seeds to mature before the first frost. The seeds naturally have a low germination rate, limiting the number of volunteer seedlings.
For successful sprouting, the soil must be consistently warm, ideally 70°F (21°C) or higher. Seeds are photoblastic, meaning they require light to germinate, so they must remain near the soil surface. Self-seeding is most reliable in mild winter regions (USDA Zones 9 and above). In cooler zones, late frost and low soil temperatures often prevent natural propagation. Older heirloom varieties, like Gomphrena globosa, are more likely to produce viable seeds than highly hybridized cultivars.
Encouraging or Preventing Volunteer Plants
Encouraging Self-Seeding
Gardeners can actively manage the self-seeding process to promote germination. To encourage a new generation of volunteer plants, cease deadheading the flowers in late summer and fall. Allowing spent flower heads to remain ensures the seeds drop naturally into the garden bed. Avoiding heavy organic mulches is also beneficial because the seeds need direct light exposure to sprout. In the spring, lightly scratching the soil surface can help expose buried seeds to the sunlight required for germination.
Preventing Volunteer Plants
If you prefer to prevent volunteer seedlings, the most effective technique is to aggressively deadhead the flowers. This should be done before the seeds have a chance to mature and scatter, removing the seed source entirely. Alternatively, applying a thick layer of mulch, such as wood chips or shredded bark, in the fall will smother any already-dropped seeds. This layer blocks the necessary light and warmth, preventing germination the following spring.
Reliable Methods for Next Season’s Growth
When relying on nature is too unpredictable, starting Gomphrena from seed indoors is the most reliable way to guarantee plants for the next season. The seeds should be sown approximately six to eight weeks before the last expected spring frost date in your region.
The process requires a warm environment, with soil temperatures maintained between 70°F and 80°F for optimal germination. Seeds should be pressed gently onto the surface of a moist, sterile seed-starting mix but left uncovered, as they need light to sprout. This indoor start provides a head start, ensuring the plants are large enough to be transplanted outdoors once all danger of frost has passed and the soil has warmed to at least 65°F. Direct sowing the seeds into the garden is possible but is a less reliable method for early blooms. This is generally only successful in warmer climates where the soil reaches the required temperature of 70°F early in the season.