Lilacs are a favourite old-fashioned shrub used for cut flowers, hedging, and landscape specimens. Most lilacs have dark green, heart-shaped foliage and clusters of blue, pink, white, or purple flowers in spring. The flowers are known for their sweet fragrance.
- Common name: Lilac
- Botanical name: Syringa spp.
- Zones: 2 to 8, depending on species. Some are more suited to warm areas; others need cool conditions.
- Size: To 30 feet tall and 20 feet wide, depending on species
- From: Areas of Asia
- Family: Oleaceae (olive family)
- Sun: Full sun is best for good bloom production. They’ll tolerate partial shade, but won’t bloom as profusely.
- Soil: Moist, well-drained soil is best, but the plants are quite adaptable to different soils.
- Moisture: Water during times of drought to ensure abundant blooms.
- Mulch: Lay a 2- to 3-inch layer of mulch over the soil around the shrub. Avoid laying the mulch directly against the plant’s stem-leave a gap of several inches to prevent disease problems.
- Pruning: Prune in early summer, once the plants have finished blooming. Remove spent flower clusters to encourage better blooms next season.
- Fertiliser: In most soils, additional fertiliser isn’t necessary.
- Seed: Sow seeds outdoors in a cold frame or a sheltered spot in the garden in autumn. Note: Seedlings from named cultivars usually won’t look like their parents.
- Cuttings: Take cuttings in early summer, after the plants have bloomed.
- Layering: Bend one of the growing shoots toward the ground in early spring. Remove the leaves along a section of the stem, gently nick the stem in that area, then bury that section under several inches of soil. Anchor the shoot down to the ground. The stem should root in about a year. After it roots, cut it from the mother plant.
- Anthracnose: If the leaves look scorched and spotted, the cause may be anthracnose. The spots may be gray, tan, or dark brown, and could be either dry or slimy. To deter the disease, prune any infected branches, dipping your pruning tool into a bleach or alcohol solution between cuts. Prune some of the inner branches to encourage good airflow in the shrub’s center.
- Aphids: These small insects often appear in large numbers on new growth. Spray them off daily with a stream of water; they will not attack a plant after being knocked off. Use an insecticidal soap or neem-oil spray for severe infestations.
- Leaf spot: In summer or autumn, the leaves develop yellow or brown spots, often with concentric rings that form a bull’s-eye pattern. To deter leaf spot, prune the plant to allow good airflow and avoid wetting the foliage in afternoons and evenings
- Powdery mildew: This disease appears in mid- to late summer. Affected leaves are covered with a grayish powder and eventually drop off. To deter the disease, prune the plant to allow good airflow and avoid wetting the foliage in afternoons and evenings.
- Scale: Scale insects crawl up plant stems and cling to the plant. They appear as small, raised spots and are easy to overlook. To deter scales, encourage beneficial insects or apply insecticidal soap or horticultural oil.
- To ensure good bloom production, it’s important to prune at the right time. Always prune right after lilacs have finished blooming. If you prune in late summer, autumn, or early spring, you will remove the next season’s flower buds.
- Some lilacs are more heat tolerant than others; southern gardeners must choose those cultivars for good performance.
- There are hundreds of selections in different sizes, bloom times, and colours. Choose carefully to ensure the best performance. Below are a few selections:
- Syringa meyeri: Dwarf type. Grows to 6 feet with lavender flowers in spring. Zones 4 to 7.
- Syringa x prestoniae: Grows to 12 feet with large heads of fragrant flowers. Zones 2 to 7.
- Syringa protolacinata: Grows to 8 feet with finely divided leaves and small blooms. Zones 4 to 8.
- Syringa reticulata: Tree type. Grows to 30 feet with clusters of creamy flowers that bloom later than other lilacs. Zones 4 to 7.
- Syringa vulgaris: Old-fashioned lilac that grows to 22 feet with heads of fragrant spring flowers. Zones 4 to 8. There are hundreds of named cultivars, such as ‘Krasavitsa Moskvy’ and ‘Wedgwood Blue’.