Home & Garden

Lilacs and viburnums are nature’s air fresheners

Once established, lilacs can live for centuries.
Once established, lilacs can live for centuries. Tribune News Service

Two of my all-time favorite flowering shrubs are lilacs and viburnums. I’ve always enjoyed walking around campus and stopping to smell the beautiful lavender and white-colored lilacs when they are in bloom. The smell takes me back to my childhood and memories of my mother cutting lilac blossoms when the buds were still tight. She would bring them inside the house, put them in a vase and let them open. The fragrant smell spread throughout the house. In my travels I have also seen old, abandoned homesteads where the lilac bushes are huge and still blooming, a testament to their staying power.

Lilacs grow best in full sun and well-drained soil. They will often take two to three years to establish themselves in a new site. Once established they can live for centuries, that is why we see them in the abandon homesteads. Soil pH may affect the plant’s growth — lilacs do well in an alkaline soil with a pH of 6 to 7.

To ensure abundant flowering, cut off all spent blossoms each year and prune the flowering stem back to a set of leaves in order to prevent seeds forming, thereby directing the energy usually spent on seeds to next year’s flower production. If this is not done, bad flowering may follow a year of good flowering.

When the plant becomes leggy, renewal pruning is required. Remove about one-third of the oldest stems at ground level each year for three years. This encourages the growth of vigorous new stems from the base. By the end of the three years, the plant should be fully rejuvenated with its blossoms once more at nose level.

The plants should be fertilized in early spring and again directly after flowering with an all-purpose fertilizer such as a 10-10-10, watered in well. And tough as lilacs are, they need supplemental water during periods of drought.

In our area, the most serious insect pests are the lilac borer and the oyster-shell scale. Borers signal their presence by leaving one-eighth-inch-sized holes in stems and larger branches, often 1 to 2 feet above ground level. Oyster-shell scale, which looks like small, elongated, brown or gray warts on the stems, can be controlled by pruning out the most heavily infested branches, followed by an application of dormant oil spray.

Lilacs can fall victim to leaf diseases in late summer and early fall. These include powdery mildew fungus and leafroll necrosis. Powdery mildew produces unsightly whitish patches on the leaves, but the problem tends to be more aesthetic than physiological. Leafroll necrosis seems to be caused by air pollution. Some lilacs have proven less susceptible than others.

On the corner of the greenhouses, near the Creamery on campus, is a Korean Spice Viburnum — Vibrunum carlesii. It is just past its prime for smelling the potent spicy scented flowers. It is also a versatile old-fashioned shrub. It blooms in midspring with softball-sized clusters of waxy pink flowers that fade to white. Bright red bunches of quarter-inch berries appear in late summer, maturing to black in fall. These stand out from the downy muted green foliage. Foliage color brightens to striking red and rich burgundy in autumn. The viburnum is a natural in the traditional shrub border or back of perennial beds. A colleague of mine planted these around the windows of her home as a foundation plant so the fragrance would come inside. This shrub is also great against long fence lines. It is a deciduous shrub that can take full sun to partial shade. It is slow growing to 4-6 feet tall and wide, or up to 8 feet in old age. Try these natural air fresheners and enjoy their beauty and smell for years to come.

Bill Lamont is a professor and extension vegetable specialist in the department of plant science at Penn State and can be reached by email at wlamont@psu.edu.