Lemon verbena has the most intensely lemony scent of any herb, sharper and more lasting than lemon balm or lemon thyme. The long, pointed leaves go into teas, sorbets, syrups, cocktails and custards, and they hold their scent dried, which few lemon herbs do. It is a deciduous shrub from Argentina and Chile that reaches 3 to 5 feet in a container and more in the ground in zones 8 to 11, with sprays of tiny lilac flowers in late summer.
In cold-winter zones it is a container plant. Give it full sun, rich soil that drains, and regular water through the growing season, and pinch it to keep it bushy. Bring it indoors before the first frost and keep it barely moist in a cool, bright spot. It drops most or all of its leaves in response to the move and the cold and looks dead for weeks; this is normal. In late winter prune it back hard, bring it into warmth, and resume watering, and new growth comes reliably.
Harvest leaves any time, and strip whole stems in late summer to dry for winter tea. Spider mites bother it indoors. Deer leave it alone. It is a different plant from the ornamental verbenas, which share only the name.
Powdery mildew
White or grey powdery coating on leaves - usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Root rot
Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.
Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.
Spider Mites
Tetranychus urticae →Fine stippling or bronzing on leaves, faint webbing on undersides, foliage drying out during hot, dry weather.
Spray foliage with a strong jet of water to dislodge mites. Apply insecticidal soap or horticultural oil to leaf undersides; repeat every 5–7 days as needed.
Aphids
Aphididae →Clusters of small soft insects on new growth and flower buds.
Knock off with a strong jet of water. Ladybirds and lacewings are natural predators. Insecticidal soap as last resort.