Caring for Your Lilac Bush

We have had a lilac bush in the backyard for years. I remember as a kid collecting the flowers in the spring and using them while my sister and I played “house” in the backyard. The bush has been forgotten until recently when we cut down all of the surrounding trees. Now it stands kinda alone over there in the side yard needing attention.

Not knowing where to start I did a ton of research and learned some things I would have never known. Here is what I have learned about caring for lilac bushes.

But before we get into that it would be helpful to know a little about the bush and what makes it special.

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Plant Profile-

The common lilac bush is a deciduous shrub that blooms in late spring. It is a member of the olive family, along with other such ornamental plants as ash trees, forsythia shrubs, and privet shrubs.

I love lilacs for their amazing smell. In reading though not all fragrance are the same. Lilacs are among the most fragrant flowers available to gardeners in cold climates and the smell of the blossoms is one of the most unforgettable aromas of the plant world.

Varieties of Lilac Bushes and Trees-

‘Wedgewood Blue’: is a compact variety of lilac bush that 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 species variety, 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 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 shrub variety stands tall at up to 15 feet in height 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 also deliver the beloved lilac fragrance. It is suitable for zones 8 through 7.

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Now that we have the profile down let’s move on to How to Grow Lilac Bushes

How to Grow Lilac Bushes

Light-

Grow lilac bushes in full sun. They will tolerate some shade but bloom best when grown in full sun. They do not do well in full shade.

Soil-

Lilac bushes prefer a rich, well-drained, loamy soil with a neutral soil pH, but they will still grow in clay soil, just not as well.

Water-

Water lilacs fully, but do not keep the soil wet. The roots do best in well-drained soil that does not stay wet. Overwatering will lead to poor blooms. It is fine to mulch around the base of the plant to help retain moisture if desired.

Temperature and Humidity-

Lilacs do best in cool-summer climates and up to USDA plant hardiness zone 7. They are not recommended for hot, humid areas, such as southern U.S. states in zones 8 or 9.

Fertilizer-

Lilac bushes can benefit from a spring feeding, as long as the nitrogen is kept in check. Too much nitrogen in the soil leads to poor blooms.

Propagating-

Anyone who has grown lilacs know how they readily they expand and spread. Most lilacs are clump-forming plants that spread via shoots extending from the trunk. To propagate a new plant, simply dig down around one of the shoots and cut it from the main plant, including the roots, then replant the shoot in beneficial soil. Water the transplant dutifully until it is established.

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 blooming is over, since these are shrubs that bloom on old wood. Prune branches to thin out the growth (for better air circulation) and to keep the height of the plants in check. In addition, cut off the dead flowers when they are done blooming. This will prevent the seed from forming and thereby promote more profuse flowering the next spring.

If you’d like to limit the height of the shrub, cut off stems that are 2 inches in diameter or larger. You can also shape the shrub by trimming smaller stems as needed. The 1/3 rule of pruning shrubs applies to lilac bushes.

We suggest Fiskars Steel Pruning Shears.

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Pests and Diseases-

Lilacs can fall prey to several pests and diseases, though certain varieties are more hardy than others. Potential threats include:

Common lilac pests:

Aphids (Aphididae family)
Citrus nematode (Tylenchulus semipenetrans)
European fruit lecanium (Parthenolecanium corni)
Fuller rose beetle (Asynonychus godmani)
Ground mealybug (Rhizoecus kondonis)
Lilac borer (Podosesia syringe)
Mice (Murinae subfamily)
Oystershell scale (Lepidosaphes ulmi)
Voles (Arvicolinae subfamily)

Common lilac diseases:

Armillaria root rot (Armillaria mellea)
Bacterial blight or canker (Pseudomonas syringae pv. syringae)
Botryosphaeria spp. (causes fungal dieback)
Botrytis blight (Botrytis cinerea)
Gray mold
Nectria spp. (causes fungal dieback)
Phomopsis spp. (causes fungal dieback)
Phytophthora spp. (causes fungal dieback)
Powdery mildew (especially prevalent in common lilacs)
Tubercularia spp. (causes fungal dieback)
Verticillium wilt (Verticillium spp.)

The best defense against these pests and diseases is to provide your lilac with optimal growing conditions. Check your plant regularly for problems, and treat or cut off diseased areas as soon as you spot them.

Helping Your Lilac Bloom

Yes, lilacs often infuriate people, because they are so slow to bloom. You have to be really patient with them. That is the bad news. The good news is that, yes, they are worth the wait.

But what is the reason, exactly, why these classic plants fail to bloom? Well, rather than zeroing in on a single explanation, look at several possible reasons behind this problem, which include (in addition to diseases and pests):

Pruning at the wrong time
Cold weather killing the flower buds
Planting your lilacs in the wrong place
The shrub in question is either too old or not old enough to produce flower buds

Why does the precise time that you prune matter? Lilacs are shrubs that bloom on old wood. This means that the flower buds for the next spring’s blooming period are set on the growth produced during the prior year. When you prune off this growth, you lose the flower buds—and, by extension, the flowers that they would have brought. That is why you are advised to prune lilac bushes right after they are done flowering (before they have set bud for next year).

The common lilac (Syringa vulgaris) is a very cold-hardy plant, but if a hard frost or a freeze comes along just as the flower buds are about to open, they can be damaged. This results in the loss of blooms for that year. There is not much that you can do to prevent this; just accept the loss and appreciate next year’s blossoms twice as much.

As with most plants, where you have planted your lilac bush very much matters. Lilacs are full-sun plants that want well-drained soil. If you made a mistake on either of these fronts when you first installed your plants, you may be paying for it now—in the form of your lilac not flowering. But there is an easy remedy to the problem: transplant your shrub to a more suitable spot.

Regarding reason number four, be aware that, while these bushes are long-lived, their flower production does tend to peter out over the decades. The solution to this problem is to perform a rejuvenation pruning on your lilacs (do not expect immediate results, though). The opposite is also true sometimes: namely, that your plant is simply too young to bloom. Give it time.

If you have a spot in your yard I highly recommend planting a lilac bush or two. Their blooms are amazing and they are great for pollinators. You can even cut a few branches and use them as cut flowers to freshen up your kitchen table.

One more note if you want to plant multiple lilacs in your yard, consider selecting ones that bloom at different times. This way, you might be able to get six weeks or more of blooms throughout the spring.