Once they’re established, lilacs don’t require much maintenance. They will typically only need watering during prolonged periods of drought, and they prefer annual fertilization. Pruning also is generally an annual task.
Light
Grow lilac bushes in full sun, meaning at least six hours of direct sunlight on most days. Lilacs will tolerate some shade, but too little light can limit their bloom. They do not do well in full shade.
Soil
Lilac bushes prefer rich, loamy soil with sharp drainage and a neutral soil pH. They can tolerate clay soil, though it might stunt their growth.
Water
Lilacs like a moderate amount of soil moisture. But soggy soil can lead to root rot and poor blooming. Water young lilacs regularly to keep the soil lightly moist. Mature plants typically will only need watering during periods of drought.
Temperature and Humidity
Lilacs bushes prefer climates that have fairly cool summers. They are not recommended for hot, humid areas, such as the Southern United States. High humidity can lead to fungal diseases on the plant. Moreover, lilacs can tolerate temperatures well below freezing, though they prefer protection from bitter cold winds, which can damage their flower buds and break stems.
Fertilizer
Lilac bushes can benefit from a spring feeding, especially if you have poor soil. However, don’t use a fertilizer that’s high in nitrogen, which can lead to poor blooming. Instead, use a balanced fertilizer, following label instructions.
Types of Lilac
There are several types of lilac bushes that vary somewhat in appearance, including:
‘Wedgewood Blue’: This compact lilac variety attains a height at maturity of only 6 feet with a spread equal to that. The flowers are contained in thick clusters of lavender blue. It thrives in zones 3 through 8.‘Yankee Doodle’: A small lilac bush with deep purple, fragrant blooms, Yankee Doodle is a bit more cold-hardy than the main species, suitable for zones 2 through 8. It grows 6 to 10 feet tall and 5 to 6 feet wide.‘Belle de Nancy’: This variety has double pink flowers (multiple layers of petals) and grows 8 to 10 feet tall and 6 to 8 feet wide. It blooms in late spring to early summer and is suitable for zones 3 through 9.‘Madame Lemoine’: Blooming with bright white double flowers, this lilac variety stands tall at up to 15 feet high and 12 feet wide. It is suitable for zones 3 through 8.‘Primrose’: Primrose is a standard-size lilac that grows 10 to 15 feet tall and 6 to 10 feet wide. It is notable for its yellow flowers that still deliver the beloved sweet lilac fragrance. It is suitable for zones 3 through 7.
Pruning
Pruning is critical for lilacs, both to promote flowering and to ensure air circulation to prevent powdery mildew and other problems. The right time to prune is just after flowering is over, as lilacs bloom on old wood. Prune branches to thin out the growth (for better air circulation) and to keep the height of the shrub in check. Cut the oldest branches to the ground, as they won’t be strong flower producers anymore, but don’t take off more than a third of the total branches. Also, prune any weak or damaged branches.
Propagating Lilacs
Anyone who has grown lilacs knows how readily they expand. Most lilacs are clump-forming plants that spread via shoots extending from the trunk. And these shoots can be used for propagation. Not only is this an inexpensive way to gain a new lilac bush, but it also prevents the existing lilac from becoming overcrowded. The best time to propagate is in the late spring to early summer to give the shoot enough time to become established before cold weather sets in. To propagate, simply dig down around one of the shoots and cut it from the main plant, keeping the roots intact. Then, replant the shoot in rich soil wherever you wish, and keep its soil lightly moist (but not soggy) at all times until it’s established.
Common Pests & Plant Diseases
Lilacs are fairly hardy shrubs and can survive most pest and disease problems. However, they are susceptible to several. The fungal disease powdery mildew is commonly seen on lilacs, especially during humid summers. It creates whitish powdery patches on the foliage. There are both chemical fungicides and natural methods for combatting powdery mildew. The disease usually won’t be fatal, but you should still treat your lilac as soon as possible to limit fungal spread. Common pests that can affect lilacs and damage their foliage include scales and borers. If you spot these tiny insects on the stems and undersides of leaves, treat your plant with neem oil or another insecticide.
How to Get Lilacs to Bloom
Lilacs generally bloom in the mid-to-late spring, though the exact timing can differ based on the variety. The conical clusters of tiny four-lobed flowers have an exceptionally sweet fragrance. The blooms only last for a couple of weeks, but they should readily rebloom each year on a healthy plant. Deadheading, or removing the spent blooms, isn’t necessary. To enjoy a longer blooming period, consider planting multiple lilac varieties that flower at different times. A lack of sunlight is often the reason for poor flowering on a lilac. Watch your lilac for a full day to make sure it isn’t in the shade for any prolonged stretch. Lightly moist soil also encourages a stronger bloom. Mulch around the shrub can help to retain soil moisture and suppress weeds that might compete with the lilac.
Common Problems With Lilacs
Lilac shrubs are typically not problem plants in the garden. But they can encounter a few common issues.
Poor Flowering
A lilac that isn’t flowering as much as it used to might need a rejuvenation pruning. To do so, remove a third of the oldest branches right after the bloom period is over. In the next growing season, remove half of the remaining old branches after flowering. And in the next year, remove the rest of the remaining old branches. New branches that flower more vigorously will replace them in a few years.
Leaves Turning Brown
Lilac leaves turning brown might be due to several factors. Insufficient water, especially for young plants, can result in browning leaves. Too much fertilizer also can damage the foliage, as can prolonged exposure to very strong sunlight. Most often, though, brown spots on the leaves are due to bacterial blight. This infection typically occurs when growing conditions for the lilac are subpar. So correcting its conditions is one of the best remedies for the disease. Also, promptly remove infected foliage to prevent the disease from spreading.
