Green Guide: Syringa spp.

Lilacs are one of the most popular flowering shrubs in the Northern U.S. gardens. They’re prized for their showy flowers in colors from pink to white to dark purple and their evocative and memorable fragrance.

They are tough landscape plants, living for a century or more in sites with full sun, good drainage and plenty of space air movement.

Recognizing the importance of lilacs to the nursery trade and the gardening public, the late Donald Egolf started a lilac improvement program at the U.S. National Arboretum in the 1970s. By collecting, evaluating and hybridizing diverse accessions, Egolf hoped to develop lilacs with superior mildew and pest tolerance, and were adapted to warmer climates (USDA Hardiness Zone 7 and higher), but also maintained their traditional fragrant flowers.

Egolf’s work continues at the arboretum with the release of three lilac cultivars.

USNA cultivars
‘Betsy Ross’ was the first lilac release from the U.S. National Arboretum in 2000. ‘Betsy Ross’ was selected for its abundant fragrant, pure-white flowers, rounded growth habit and adaptability to Zones 5-8. Its thick, green leaves, which turn yellow in fall, show good field tolerance to powdery mildew.

It’s a multistemmed shrub that grows up to 10 feet high and 13 feet wide at maturity in Zone 7b.

‘Old Glory’ was selected for its relatively slow-growing, rounded habit, disease-tolerant foliage and profusion of fragrant, bluish-purple flowers. It grows up to 12 feet high and 13 feet wide in 25 years in Washington, D.C. it’s hardy in Zones 5-7.

‘Declaration’ is for the traditional cooler lilac-growing regions (Zones 5-6). It was selected for its large, fragrant dark reddish-purple inflorescences and an upright, broadly vase-shaped growth habit. Foliage turns deep burgundy in fall.

These selections are not patented.

Propagation
Most cultivars are relatively easy to propagate by rooted cuttings taken from new growth just after flowering, or commercially by grafting, budding or tissue culture.

New plants grow quickly in containers and will usually bloom the first year after propagation. Because the root system in shallow, transplant when plant is dormant or not actively growing – early to late fall.

In the landscape
Besides their beloved flowers, lilacs owe their popularity to their versatility in the landscape. They can be used as specimen plants, especially along sidewalks or paths where their fragrance will be fully appreciated.

Use as an early blooming focal point in a shrub border, as background plantings for a perennial garden, as a screen or hedge, or mass planted.

Lilacs are tolerant of selective pruning to maintain shape and size, while older plants can often be effectively rejuvenated by pruning back to the ground.

— Margaret Pooler, U.S. National Arboretum