Purple verbena, a moderately fast growing perennial sometimes grown as an annual, blooms profusely on a low-growing, bushy plant. It makes a beautiful border edging, spilling over a rock wall, or softening the edge of a sidewalk or path. Verbenas require well-drained soil, and prefer moderate summer climates; blooming wanes during very hot weather. Although purple verbena tolerates cutting back, it's important to know when to trim, and how much trimming is appropriate.
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Cutting Back to Stimulate Blooming
Cut back purple verbena if blooming wanes in midsummer. Trim a quarter of the height and width of the plant using grass cutters or scissors. Then, water the purple verbena thoroughly, and apply liquid fertilizer diluted to half the strength recommended by the manufacturer for standard use.
Cutting Back in the Spring
Cut back the tips of the stems of your purple verbena in the spring to encourage branching. You'll have stockier, bushier plants with more blooms as a result. Water the plant thoroughly and apply fertilizer to further encourage growth and blooms.
Cutting Back in the Fall
If the purple verbena begins to look shaggy and unkempt in the late fall, trim it back very lightly to neaten the appearance. However, avoid cutting it back severely; the shocked and dehydrated plant will be weakened going into the winter. Water the purple verbena thoroughly after a fall trimming to help the plant recover and prepare for winter. If your purple verbena reseeds itself, and you want it to continue to do so, avoid removing most of the spent blooms in the fall trimming. The blooms will produce the seeds that will insure new seedlings for next spring.