Lemon verbena has the most intensely lemony scent of any herb — far sharper and more persistent than lemon balm or lemon thyme. The long, pointed leaves are used in teas, sorbets, cocktails, and as a finishing herb. In Zone 6b it must be grown as a container plant and overwintered indoors; it drops its leaves in response to cold, looking dead before bouncing back in spring warmth.
Bring indoors before first frost and keep barely moist in a cool, bright spot. It will drop most or all of its leaves — this is normal. Prune back hard in late winter, bring into warmth, and resume watering; new growth emerges reliably.
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.