Lilacs are found growing (where winters are cold enough to afford proper growth and ample blossoms) from the smallest rural village to the urban courtyard. They grow the very best in zones 3, 4, and 5, in the colder regions of zones 6 and 7, and in the warmer regions of zone 2. They will tolerate temperatures of -35 to -40f, though they may suffer some damage from windchill. If temperatures dip to such extreme cold in your region, site the lilac out of the path of chilling winter winds. Lilacs will tolerate frozen ground but not frozen pockets where water does not drain properly. Requiring excellent drainage, they grow best along rocky, limestone hillsides, suggesting just how important good drainage is. When planted in a mesic site, lilacs flower adequately, although, by late summer the foliage may wilt and turn moldy.
Lilacs perform best in sandy, gravelly loam mixed with organic matter such as compost and aged manure. Keep the surrounding soil free from weeds with an annual mulch of compost. In early spring sprinkle a cup of wood ashes around the base of the lilac and work it gently into the top layer of soil. Every three years or so apply a cup of ground limestone to the soil, again gently working it into the soil so as not to injure the roots.
Lilacs require full sun to nearly full sun to set flower buds. Where optimal sunlight isn’t always available, one may have some success with pushing the envelope. We are growing lilacs in several locations in half sun, and although they would be fuller in form with far more flowers, all are growing well.
The overall shape of lilacs is greatly improved with an annual pruning. Immediately after flowering is the ideal time to attend to this not unpleasant task. The job becomes less manageable as the shrub grows tall and leggy in a few short years.
After the lilac has become established and is a desirable size and shape, cut to the ground approximately one third of the oldest branches and thinnest suck- ers. This allows the bush to renew itself and for the energy of the bush to go into the remaining growth. Leaving the strongest trunks that form the armature of the shrub, prune diseased or pest-infested shoots or branches, and remove all declining stems, thin suckers, and small, twiggy branches. Some lilacs produce suckers rarely, if at all, and others sucker aggressively. Remove all spent flowers immediately after blooming, snipping very close to the tail end of the panicle so as not to remove the new growth that will provide you with next year’s flowers.
If you are growing lilacs as a background shrub or as a small tree, allow only two to three main stems as trunks, removing lower branches and cutting all other shoots to the ground. ’Beauty of Moscow’, ‘Madame Florent Stepman’ and the common lilac, both var. purpurea and alba, are all well suited for growing into a small multi-stemmed tree. Conversely if you do not want your lilac to become a tree, prune to a height of eight to nine feet, which keeps the blossoms at eye level.
With its versatile form and lovely heart-shaped leaves the lilac is an exceptional companion to a wide range of flowering trees and shrubs. The extended period of florescence a well-planned lilac hedge provides coincides with the long flowering period of our native pagoda dogwood (Cornus alternifolia) and Catawba rhododendrons. Just as the Sargent crabapple (Malus sargentii) is at its flowering peak, with masses of sublimely scented white blossoms, the earliest lilacs begin their fragrant parade. In our garden, the blossoms of Prunus, namely peach, pear and plum, overlap with the flowering of ‘Beauty of Moscow,’ ‘Maidens Blush,’ and ‘President Grevy.’ They are planted in close vicinity along the garden path. The newly emerging fragrant blossoms of Prunus interwoven with the pervasive perfume of lilacs give The Scent of All Spring!
Lilacs are one of the loveliest shrubs to grow as a tall hedge, and they integrate magnificently into the country hedge of mixed shrubs and trees. The ineffable beauty and fragrance of lilacs are enhanced by the many varieties of suitable companion plants. The short list of plants described here is particularly appealing during the lilac’s period of flowering, for their compatible scents, colors, and foliage or for creating a sequentially blooming combination of fragrances. ‘Korean Spice’ viburnum, nearing the end of its florescence while the lilacs are beginning theirs, blooms in pink infused white, snowball shaped flower heads, with an intensely sweet and spicy aroma. Variegated Solomon Seal, Viola ‘Etain,’ late-season jonquils and narcissus, and lily of-the-valley all bloom simultaneously with early lilacs. The most sublimely scented tree peony ‘Rockii,’ with white petals washed with pale rose, and magenta-purple splotches at its heart center, also flowers during lilac time. Later in the season, to coincide with later-flowering lilacs, come the Iris pallida , Iris germanica, and native Iris versicolor, English bluebells, early species daylilies with their honey-citrus scent, ‘Bridal Wreath’ spirea, blue and white columbine ‘Origami,’ and white bleeding hearts (Dicentra spectabilis ‘Alba’). Although not at all fragrant, I find the warm, rich yellow color of native honeysuckle Lonicera ‘John Clayton’ particularly appealing with the white and cool blue-lavender-hued lilacs. Just as ‘Therese Bugnet,’ the earliest of roses to flower (with its Rugosa heritage) joins the scene, the lilacs are finished for the season. Lilacs, when pruned to a small tree shape, allow a variety of plants to grow happily at their feet. Herbaceous peonies, although their blooming period usually does not coincide with lilacs, make an ideal garden companion. In our yard, Paeonia lactiflora follow lilacs almost to the day in order of sequential blooming. The dense, full mounds of foliage of the herbaceous peonies visually fill the space left by the trunk of the lilacs, as do hosta. The foliage of hosta, planted on the shady side, makes a companionable partner. Hosta will appreciate the filtered sun and both plants benefit from an annual blanket of compost. Species daylilies, Montauk daisies, and chrysanthemums are ideal companions when planted on the sunnier side of lilacs.
Spring never lasts long enough in New England, with some years leaping from bitter cold to balmy, summer-like temperatures. Despite freezing rain and late spring snow, lilacs bloom and bloom resplendently. For the extended period of time in which the spires of sweet florets are in bloom, our garden is redolent with their heavenly fragrance. The blossoms of Syringa vulgaris, and especially the fragrant sorts, are a nectar source for the Eastern Tiger Swallowtail. The diminutive “violet afloat,” better known by its common name Spring Azure, is captivatingly beautiful floating about the pure white flowers of ‘Marie Legraye.’ Throughout the seasons our lilac hedge is alive with a chattering collection of songbirds. The height and the crooks of the branches are enticing to the innumerable songbirds, though it is the cadmium orange oriole alighting on the blue-hued spires of ‘President Grevy’ that causes the heart to skip a beat.
End Notes: Occasionally one must dig a bit deeper to find the value of a plant in relationship to pollinators for the landscape designed for people and wild creatures. First and foremost a garden should be an inviting habitat for the people who dwell there. What better way to create an invitation than with the beauty and fragrance of the lilac? Although not native to North America, lilacs (Syringa vulgaris) are celebrated in this country as they are part of our cultural heritage. From cuttings tucked into belongings, the earliest settlers connected their previous home to their home of new beginnings. The ease in which lilacs are cultivated is famous and testifies to their success and popularity. At a lecture I attended not too long ago, an example of a white oak, which supports nearly one hundred species of Lepidoptera, was compared to the lilac, which is known to support just twenty-five. From a gardener’s perspective that is like comparing apples to oranges. Very few have space enough to grow an 80-foot-tall white oak, whereas a ten-foot-tall and easily cultivated lilac can find a place in nearly any garden. Besides, twenty-five species of Lepidoptera is not bad. Additionally, lilacs are a rich source of nectar for swallowtails. Our native eastern redbud—although stunning, and providing nectar for bees and hummingbirds—is much more challenging to cultivate and hosts two species of Lepidoptera. Plant what you like, as long as it is not invasive in your particular region. As much as possible, utilize native plants in your garden design and combine with well-investigated and well-behaved ornamentals.
For an expanded version on the history of lilacs, Lilacs the Genus Syringa written by Fr. John L. Fiala is highly recommended. Filled with hundreds of color photographs and including chapters on the culture of lilacs, hybridizing techniques, and propagation, I have turned to this book repeatedly. Fortunately it has been reprinted and is once again available through Timber Press.