Things You'll Need
Garden cultivator or hoe
Rags or paper towels
Sun-loving verbena (Verbena x hybrida), a butterfly favorite, is sometimes described as a see-through plant, because its long flowering stems do not obstruct the view of other bedding plants and flowers. Depending upon the variety, verbena grows in U.S. Department of Agriculture plant hardiness zones 7 through 10 as a perennial, and in USDA zones 6 and below as a tender annual outdoors or in containers. Verbena does best in a sunny and well-drained spot. Considered a low-maintenance plant, it generally requires little care beyond the basics.
Trim all plants surrounding your verbenas if necessary to allow them to receive eight to 10 hours of full sun daily. Too little sun can limit flowering and make plants susceptible to powdery mildew. Move potted plants as needed to maximize the amount of sun they get each day.
Remove surrounding plants so each verbena has 1 1/2 to 3 feet of space surrounding it. Trim the lateral or side growth on nearby plants or remove them entirely if they are crowding out the verbenas. Good airflow around verbenas helps prevent disease.
Apply 1 inch of water at least once a week or whenever the soil appears dry, but not to the point of saturation. Water the plants at soil level and not from overhead, digging into the soil to a depth of 6 inches to check for moisture and watering until the soil is damp to that depth. Check the soil moisture about once a week during average weather and every other day during hot, dry weather.
Pinch or snip off dead flowers on verbena plants regularly to encourage more blooming.
Prune the plants back two or three times during the growing season by about one-fourth of their height and spread or whenever blooming slows. This helps encourage more flowers.
Spread a complete slow-release fertilizer, such as 19-5-9 or 16-4-8, at least once a month during the growing season at a rate of 1 pound per 100 square feet of garden.
Inspect your verbenas regularly for signs and symptoms of pests, such as the pests themselves, discolored or distorted leaves, holes or chewed edges in flowers or foliage, trails in leaves and the sticky honeydew produced by aphids. Check for powdery mildew, which appears as a white, downy substance on leaves and along stems.
Treat plants infested with spider mites, aphids and thrips by rinsing the leaves with a strong spray of water or spraying with homemade insecticidal soap made by mixing 2 teaspoons of dish detergent with 1 quart of water in a spray bottle. Spray the plant until the solution runs from the leaves.
Dilute 2 teaspoons of neem oil in 1 gallon of water and spray the solution on the entire plant if the verbena has powdery mildew or a difficult-to-treat pest infestation. Wear gloves, long sleeves, long pants and protective eyewear when working with neem oil because it can irritate the skin or damage your eyes.
You can buy verbena plants from a nursery or garden center, or you can germinate your own seeds 12 to 14 weeks before the last frost date for your area. The seeds must be started in complete darkness, and germination can take up to 30 days at a constant temperature of 70 to 75 degrees Fahrenheit. You can also sow verbena seeds directly into the garden in the early spring or fall.
Always disinfect pruning shears and other cutting tools before using them by wiping the blades with a cloth or paper towel dipped in isopropyl alcohol.
Purple top vervain (Verbena bonariensis), which grows in USDA zones 7 through 11, and shore vervain (Verbena litoralis), which grows in USDA zones 9 through 11, are considered invasive plants in California and elsewhere. The U.S. Forest Service advises close management of ornamental and invasive plants and reporting any infestations to a land management agency.
- Clemson Cooperative Extension: Verbena
- Colorado State University: Insects on Flowers
- Calflora IPC Watch List: Verbena Bonariensis (Purple Top Vervain) & Verbena Litoralis (Shore Vervain)
- The Garden Helper: Everything You Need to Know About Growing Verbena Plants
- U.S. Forest Service Pacific Northwest Research Station: Invasive Species
- Missouri Botanical Garden: Verbena Bonariensis
- Texas A&M Agrilife Extension: Verbena--Queen of Summer Beauty
- University of Florida IFAS Extension: Disinfection of Horticultural Tools
- Gardener's Supply Company: When to Water
Rachel Lovejoy has been writing professionally since 1990 and currently writes a weekly column entitled "From the Urban Wilderness" for the Journal Tribune in Biddeford, Maine, as well as short novellas for Amazon Kindle. Lovejoy graduated from the University of Southern Maine in 1996 with a Bachelor of Arts in English.