Common lilac (Syringa vulgaris) is a deciduous shrub native to the Balkan Peninsula and one of the most widely grown ornamental shrubs in temperate gardens. Specimens regularly live more than a century and are often found thriving around long-abandoned homesteads. Spring flower clusters appear in shades of purple, lilac, pink, and white and are among the most recognizable fragrances in the garden.
Lilacs bloom on old wood, so pruning must happen immediately after flowering ends — cutting in late summer or fall removes next season's buds. The shrub requires at least six weeks of temperatures below 45°F to set buds reliably and performs poorly in mild-winter climates. It spreads by root suckers, which should be cut at ground level as they appear if a tidy, single-stemmed form is desired. Optimal soil pH is 6.5–7.5; acidic soil suppresses flowering. Keep mulch several inches away from the base to prevent crown rot. Rejuvenate severely overgrown plants by removing one-third of the oldest, thickest stems at ground level each year for three consecutive years.
Lilac flowers are edible and used in syrups, infused honeys, flavored sugars, and baked goods. The bark has been used in European folk medicine as a febrifuge and bitter tonic.
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.
Verticillium Wilt
Lower leaves yellow and wilt, often on one side of the plant, with brown streaking in the stem and crown tissue when cut open. Plants are stunted and decline over the season.
Remove and destroy affected plants. Avoid planting in soil that has grown infected tomatoes, peppers, or other susceptible crops. Rotate beds and improve drainage; there is no cure once a plant is infected.
Lilac Bacterial Blight
Young shoots wilt and collapse rapidly, turning brown to black. Leaves develop brown, water-soaked spots that expand and merge. Infected stems may form dark cankers and the shoot tip often bends into a characteristic shepherd's-crook shape. Damage is most severe in cool, wet spring weather.
Prune all affected shoots 6–8 inches below any visible symptom. Sterilize pruners between each cut using 70% isopropyl alcohol or a 10% bleach solution. Bag and dispose of infected material — do not compost it. Avoid overhead irrigation. Where blight recurs annually, apply a copper-based bactericide at bud swell and again at early leaf emergence.