Germination temperature
About 21-25 °C (70-77 °F); no germination at 10 °C (50 °F).
Flower growing guide
Garden verbena gives months of flat flower clusters in red, pink, purple and white, but its seed is famously erratic. The secret is warmth and a compost that is moist but never wet.
About 21-25 °C (70-77 °F); no germination at 10 °C (50 °F).
Cover very lightly, about 2-3 mm (1/8 in) of fine vermiculite or compost.
Often about 2 weeks; stragglers can keep coming for much longer.
Light cover only; light on the tray can improve germination.
None needed. Avoid soaking.
Start in trays or modules and transplant.
Garden verbena seed is long, thin and brown. Germination varies by variety and seed lot because of differences in the seed coat, so sow about twice as many seeds as the plants you want. Store unused seed dry and sealed; dry, sealed seed kept its quality best in a South African seed-quality study.
Not needed. Research shows the seed takes in oxygen through a small opening at its scar (the hilum); damaging the coat does not help.
Not needed as a routine. Chilling the seed before sowing has sometimes helped slightly, but results were inconsistent.
Do not soak. In free water the opening that lets oxygen into the seed swells shut (by 45-86% in one study), and germination drops. Wet seed is the most common reason verbena fails.
Keep the tray at about 21-25 °C (70-77 °F). Germination stops at a constant 10 °C (50 °F) and is clearly reduced at 15 °C (59 °F) or under erratic temperatures; a steady day/night swing between about 28 °C and 14 °C (82 °F and 57 °F) is fine. In the plains of India, sow after the monsoon, when days are warm but the air is drier.
Scatter seed on the surface and cover with a thin layer, about 2-3 mm (1/8 in), of fine vermiculite or sieved compost. Do not bury it deeply.
Fine, free-draining seed compost; add a quarter perlite if your compost holds a lot of water. Use clean trays.
This decides success. Water the compost before sowing, then keep it only just moist. Water from below and let the surface dry slightly between waterings. Cover the tray to hold humidity for the first few days, then vent it daily so condensation does not drip onto the seed.
Seed germinates under its light cover, and in a germination study continuous light raised germination from 35% to 50% compared with darkness. Put the tray in bright, indirect light.
About 14 days at 24 °C (75 °F) and about 21 days at 17 °C (62 °F) in a germination study. Verbena is often slow and erratic, so keep the tray going for several weeks before giving up.
Move seedlings to small pots or modules once they have two true leaves. Handle them by the leaves and water in lightly.
After emergence keep seedlings at about 21-24 °C (70-75 °F), then lower the temperature step by step to about 16-18 °C (60-65 °F) as they grow, in full light. Pinch out the tip when plants have three or four pairs of leaves to make them bushy.
Harden off and plant out after the last frost in frost climates. Choose full sun and space plants so that grown neighbours only just touch, which keeps air moving through the leaves; in pots and baskets several plants can share one container.
Cause: compost too wet, temperature too low, or naturally low germination of the lot. Fix: keep the compost barely moist at 21-25 °C (70-77 °F), never soak the seed, and sow extra.
Cause: damping off in wet, cold compost. Fix: clean trays, free-draining compost, bottom watering and good air movement once seedlings are up.
Cause: powdery mildew, common on garden verbena in crowded, shaded beds. Fix: full sun, wider spacing and water at soil level.
Cause: thrips or spider mites in hot, dry weather. Fix: rinse plants, remove badly affected shoots and use insecticidal soap if numbers build up.
Garden verbena flowers best in full sun and well-drained soil. Raised beds and pots help during heavy rain, when roots rot in waterlogged soil.
Trim off faded flower heads to keep new clusters coming over a long season.
Plants in garden soil need little feeding. In pots and baskets start a potassium-rich liquid feed, such as tomato fertilizer, about a month after planting.
Treat garden verbena as an annual. In frost climates sow in late winter for summer flowers; in warm climates a post-monsoon sowing flowers through the cooler months.
Sow garden verbena warm and barely moist for a long season of bright flower clusters.
The seed breathes through a tiny opening that closes when it sits in water, so wet compost suffocates it. Keep the compost barely moist and warm, and germination improves a lot.
It is not necessary. Chilling has given inconsistent results in trials; warmth, a light covering and careful watering matter more.
No. Garden verbena is a hybrid with broad clusters of large flowers; moss verbena is a different, finely cut, spreading species. Both are now placed in the genus Glandularia and germinate in similar warm conditions.