Verbena is a popular ornamental plant known for its long season of vibrant, clustered blooms. It can be grown as an annual in cooler regions or as a perennial in warmer climates. Starting verbena from seed is a slow process because the seeds possess a natural dormancy mechanism that must be broken for reliable germination. Successfully growing these flowers requires precise timing and environmental control.
Essential Preparation Before Sowing
Verbena seeds exhibit innate dormancy, resulting in low germination rates unless a specific pre-treatment is applied. The most effective method is cold stratification, which simulates the seeds overwintering in cold, damp soil. This cold period breaks down germination inhibitors within the seed coat, signaling that spring is approaching.
To cold stratify the seeds, place them in a container mixed with a moistened medium like sand or a damp paper towel. The sealed container should then be placed in a refrigerator, where the temperature is consistently cool. A period of chilling for three to six weeks is recommended to satisfy the cold requirement. After this chilling period, the seeds are ready to be sown indoors under warmer conditions.
Optimal Timing for Starting Seeds Indoors
Start verbena seeds indoors 8 to 12 weeks before the last expected spring frost date. This early start is necessary because verbena seeds are slow to germinate, often taking 20 to 40 days to sprout even after stratification. Starting them early ensures the seedlings are mature enough for transplanting once the weather stabilizes, allowing for blooms in early summer.
After cold treatment, sow the seeds on the surface of a sterile seed-starting mix and lightly cover them with soil or vermiculite. Many verbena varieties require light for optimal germination, so avoid burying them deeply. Maintaining a consistent soil temperature of 70 to 75°F (21 to 24°C) is ideal for encouraging growth.
Using a heat mat beneath the seed tray is often necessary to provide bottom heat, as ambient room temperature is frequently too cool for reliable sprouting. Once germinated, they require strong, direct light to prevent them from becoming weak and elongated (etiolation). Bright grow lights positioned a few inches above the emerging plants support healthy, compact growth during the indoor phase.
Transitioning Seedlings Outdoors and Direct Sowing
Before planting verbena outdoors, “hardening off” is necessary to acclimate them to harsher environmental conditions. Indoor seedlings are accustomed to stable temperatures and filtered light, making them susceptible to shock from direct sun, wind, and cool temperatures. The hardening off process should take seven to fourteen days, starting by moving the seedlings to a sheltered outdoor location for a few hours daily.
Progressively increase the duration of outdoor exposure each day, including more direct sunlight and wind. Final transplanting should occur only after all danger of frost has passed and nighttime temperatures remain reliably above 50°F (10°C). Planting too early risks damaging the tender seedlings, as verbena is not tolerant of cold weather.
Direct sowing the seeds into the garden soil is generally less reliable than starting them indoors, especially in regions with shorter growing seasons. If you choose to direct sow, it should be done in late spring after the soil has warmed and the last frost has occurred. For best results, the seeds should be surface-sown or barely covered in a prepared garden bed. This method is usually only practical in warmer climates with long growing seasons, or by sowing in the fall for natural cold stratification.