14 Tips To Keep Your Lilacs Blooming All Season

Looking to get the biggest and brightest blooms out of your lilacs this season? There are actually several things you can do to encourage the flower growth of these prolific bloomers. In this article, certified master gardener Liz Jaros walks through her top tips for getting the most out of your lilacs this year!

lilacs blooming

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In temperate climates, where winters are cold and summers are warm, lilacs rule the landscape in spring. In rural and urban settings alike, sweet-smelling, oversized panicles erupt from seemingly ordinary shrubs and trees to deliver a powerful pastel punch. But only for a couple of weeks.

Lilac season is short and fleeting, and that’s definitely part of its allure. Despite the brief performance, lilacs continue to be one of the most appreciated and easily identifiable plants in hardiness zones 3 through 7. And though the growing season is quick, any gardener who’s ever tended to the needs of these graceful cottage charmers will tell you it’s worth all the effort.

So let’s look at 14 ways you can help your lilacs achieve bountiful, beautiful blooms that last as long as possible and a healthy growing habit that lasts all season long.

Know Your Variety

With 25+ species and thousands of cultivars, lilacs range in height from 3-foot ornamental shrubs to 30-foot trees. Diverse in stature and personality, lilacs send up blooms of white, violet, blue, lilac, pink, magenta, or purple from early spring to early summer.

If you know your lilac’s exact species and cultivar, then you know its approximate bloom time and you’re ahead of the game. If you’re not quite sure what kind of lilac you’re working with, take some time to observe its behavior and you should be able to narrow it down considerably. Once you’re familiar with its habit and flowering pattern, you’ll be able to put a proper maintenance plan in place.

Here’s an overview of some of the most common lilac species and their main characteristics:

Common or French (Syringa vulgaris)

Syringa vulgaris
Common lilacs reach 20 feet in height, and produce magnificent fragrant flowers.

This is the lilac species that typically comes to mind for all of us. A fast-growing shrub with a wild habit that can reach heights of 20 feet, common lilacs typically feature smooth, heart-shaped leaves and traditional, cone-shaped blooms that are very fragrant.

Lilacs in this species flower in mid to late spring. This is one of the most popular sun loving varieties, so keep that in mind depending on where you are going to plant them!

Littleleaf (Syringa microphylla)

Syringa microphylla
Littleleaf lilac is a late-flowering small ornamental shrub.

This small, round ornamental shrub comes in sizes that do not exceed 5 feet. It features small, fragrant, late blooming flowers and makes a nice accent plant. Littleleaf lilac varieties bloom in mid to late spring.

Persian (Syringa persica)

Syringa persica
Persian lilac produces small, pale flowers that bloom from late spring to early summer.

Growing 3-4 feet tall and 8-10 feet wide, persian lilacs feature tight branching and a more compact habit. Flowers are small and pale in color, with a late spring to early summer bloom time. Persian lilacs have small, narrow leaves, so they take shearing well and are commonly used as low hedges.

Tree (Syringa reticulata)

Syringa reticulata
Syringa reticulata produces large clusters of creamy flowers with a pleasant fragrance.

Large clusters of creamy to white flowers explode in early summer on most tree form lilacs, emitting an odor that some find pleasing and some find unpleasant. Leaves are oval and shiny. Trees may be single or multi-stemmed and max out at 30 feet in height.

Plant in Full Sun

Shrub blooming in full sun in the garden
Lilac grows well in full sun for at least 6 hours a day.

Lilacs are sun lovers and need at least 6 hours of direct light per day in order to flower to their fullest potential. While their stems and foliage will usually grow just fine beneath a dappled tree canopy or in an area that gets less than 6 hours, their blooms will not be as robust.

Lilacs that are planted in full shade will be leggy and sparse, with little to no blooms. If you find that your lilac is suddenly shaded due to maturing trees or nearby shrubs, consider having the tree canopies limbed back or thinned out. And prune nearby plant material to keep the sun shining generously on your lilac, whenever possible.

Keep in mind that 6 hours of sun does not necessarily mean 6 consecutive hours. If your lilac gets a few hours here and a few hours there, that can be just fine, as long as the total is 6 and the sun is direct.

Keep Root Flares Exposed

 gardener planting tree in garden
Plant lilacs so that the root shoot remains 1 inch above the soil level.

In-plant language, the term root flare refers to the point at which the trunk connects to the root ball. Look for the spot where the trunk gets wider and flares out at your lilac’s base.

Lilacs should be planted with the root flare about 1 inch above soil level. This will ensure that water and air flow properly and encourage the topmost roots to spread outward rather than circle the trunk.

Make sure you’re not piling mulch up around your lilac’s base as this will inhibit proper drainage and encourage pest and disease. Keep mulch pulled 3 or 4 inches away from lilac stems and don’t plant grasses or perennials too close to their trunks. They will be happier, healthier, and more floriferous.

Water Enough, But Not Too Much

gardener watering a purple flowering shrub
Lilacs are recommended to be watered deeply and slowly once a week.

Lilacs prefer well-drained soil and do not flower well if their feet are wet. Make sure your lilac is not planted in a low area, near a downspout, or adjacent to a plant that requires excessive watering.

While lilacs will require regular, even watering during their first year, they rarely need supplemental watering in subsequent years. Give them a deep, slow soaking once a week in spring and twice a week in summer for best results. As they do not like wet feet, make sure drainage is good and soil never puddles.

With that said, in times of severe drought, they may need a little extra attention. If leaves are droopy and the weather’s been hot, hit them with the hose now and then. They will thank you during peak season with beautiful blooms.

Monitor Your Soil

organic soil in hands
Make sure the soil is well-drained and does not retain standing water.

After you water, if drainage is not quick and even, you might want to check the soil around your lilac’s stems. If it is sticky and clay-based, work a little peat into the area, possibly even a little sand.

Strive to create a bed that drains evenly and does not hold standing water. Conversely, if the soil around your stems appears dry or washes away too easily, add some organic matter to give it a better consistency.

You might also want to perform a soil test to make sure your lilacs have the best possible growing conditions. Lilacs prefer neutral to slightly alkaline soil. Shoot for a level somewhere between 6.5 and 7. If pH is too low, add a little lime to increase acidity. If it’s too high, work some sulfate or bone meal into the dirt.

Deadhead Spent Blooms

Deadheading spent blooms in garden
To make lilacs produce more flowers, be sure to cut off faded buds.

Since dying flower heads are an indication that seed production has begun, a flower’s growing system will then divert its focus from creating showy blooms to nurturing its roots and foliage.

When we remove spent or fading flowers from a healthy plant, we are actually tricking the plant into thinking it should send up more blooms.

Since lilacs bloom on old wood and generate buds for next year very soon after this season’s flowers have faded, deadheading spent lilac blossoms will encourage the plant to direct its energy toward creating bountiful, beautiful buds rather than boring old roots and leaves. 

On reblooming varieties such as ‘Josee’ and ‘Bloomerang,’ deadheading lilacs after the first wave of blooms will encourage a more robust flower show during subsequent blooms throughout the season. 

To deadhead properly, use a small bypass pruner or scissors to remove spent blooms with a sharp cut just above the first set of leaves you encounter as you slide your fingers down their stems.

Remove Suckers

gardener removing suckers using a lopper
It is recommended to remove lilac suckers using a lopper.

If you see some random branches with leaves rising from the dirt around your lilac’s trunks, those are called suckers and should be removed. Growing directly from your plant’s roots, suckers do not flower or form side branches and they will drain energy away from the plant’s canopy or upper body.

Using a lopper, remove suckers right where they emerge from the root—you may need to pull away some soil to get at the sucker’s base. Performing this routine maintenance task will redirect nutrients and energy toward creating beautiful flowers.

Thin Them Out

cut branches lie on the ground with a lopper
Identify the oldest lilac stems and cut them back to allow sunlight to reach the inner leaves of the plant.

Considered routine maintenance in most lilac shrubs, ‘renewal pruning’ involves cutting out roughly ⅓ of existing stems at the base. Begin with the oldest and tallest stems as well as those that are dead, crossing, or broken. Look for the thickest, woodiest stems to determine the oldest. They will usually be gray and have significantly fewer branches and leaves than newer growth.

Sometimes called ‘thinning,’ this technique will open up your lilac’s center, which will allow more sunlight to reach inner leaves, allow more water to reach roots, and encourage proper air circulation. It’s a good technique for managing fungal disease, increasing bloom production, and keeping shrubs at their optimal size.

Cut Them Back

Shrub branches with new foliage
Another way to resume lilac bloom is to rejuvenate pruning.

If your lilac is growing out of control, has gotten leggy, or has stopped blooming altogether, you can cut the entire plant down and encourage it to start over. This process, called a rejuvenating prune, should be done during their dormant period, when it will not be stressed by the procedure. It is an exception to the ‘prune immediately after blooming’ lilac rule.

Keep in mind, however, that your lilac will not be blooming again for a few years. This is a long-game strategy for restoring your lilac to its original glory and it requires patience. Here’s how it’s done:

Steps For Cutting Back

  • Start in winter or early spring.
  • Use a pruning saw to cut evenly through their stems.
  • Cut at a height of 6-8 inches above ground.
  • This will encourage multiple new shoots to sprout from the plant’s roots.
  • Next season in winter or early spring choose the healthiest looking shoots to remain.
  • Prune off all others at the base.
  • Prune the remaining shoots back to just above a bud or leaf.
  • This will encourage side branching.
  • The following year you can resume normal maintenance pruning until it fills out.
  • This should help maximize your blooms.

Give Them Plenty of Space

Trees planted at a distance from each other
When planting lilacs, consider the distance between plants, as lilacs require good air circulation and plenty of sunlight.

Lilacs have very large, aggressive root systems. You can expect them to be as wide as the plant’s foliage or canopy. The area where they’re planted needs to be able to accommodate their size at maturity. When lilac roots are crowded, flowering will be reduced. So, it’s important to consider this when you’re deciding where to plant.

Lilacs also require good circulation in order to draw enough sun and fend off disease, so they can’t be planted too close to each other (or to anything else).

This can be one of the hardest rules to follow, especially when you’re working young, small plants. Do it anyway. You will reap the rewards with many long seasons of full-throated blooms.

Don’t Over-fertilize

man holding fertilizer
For lilacs, the ideal fertilizer ratio is 5-10-10.

Lilacs are strong feeders and do not typically need more than an early spring shot of fertilizer. Some horticulture professionals claim that lilacs need no supplemental fertilizer at all.

It’s really a judgment call. But if you feel like they need a boost, look for granules, spikes, or a slow release formula. These fertilizers will deliver nutrients gradually each time you water.

As too much nitrogen will make them leggy and leafy, rather than full and flowery, try a fertilizer ratio of 5-10-10, since you’ll want less nitrogen and more phosphorus and potassium (which encourage blooms).

Feed lilacs annually in early spring. Repeat bloomers (Bloomerangs) can get another dose later in the season. Follow your product instructions for quantities and application.

If they are planted in the grass or near grass that’s being treated and fertilized, protect them from getting too much incidental nitrogen or blooms will suffer.

Monitor Diligently For Pests & Diseases

While lilacs are pretty hardy and resistant to disease, they do have some vulnerabilities and should be monitored regularly for signs of stress. Be on the lookout for the following issues that can negatively affect bloom quality and duration:

Powdery Mildew

Powdery Mildew
Powdery mildew is the most common lilac disease that occurs due to high humidity and dampness.

By far the most common lilac affliction, powdery mildew presents with white, chalky leaf splotches that turn gray or black later in the season. Typically, your first signs of it will appear on lower leaves in times of high humidity and moisture.

While powdery mildew is an aesthetic issue and does not typically have a big impact on blooms, it will affect the overall look of the plant. Once it’s been identified, it should be managed promptly.

Cut off affected leaves, or ignore them completely until the flowering season is over, then give your lilac a good prune. Promptly remove fallen leaves and branches, as mildew can overwinter in the soil and show up next year.

Bacterial Blight

Bacterial Blight
Bacterial Blight is manifested by brown-black halos on the leaves or blackened flower buds.

Another moisture-related lilac disease, bacterial blight presents with brown-black leaves, distorted shoots, and sickly flowers. You might see yellow halos on your leaves or blackening flower buds if you catch it early enough.

Caused by bacteria that is always present on lilac leaves but flourishes when they’re wet, blight makes lilacs more prone to damage from the cold. Again, proper watering and aggressive pruning is key to management.

Lilac borer

Lilac borer
Trim lilac branches infected with a lilac moth.

This is the most common lilac aggressor and is typically found on older branches first. Look for cracked bark, broken branches, and/or stem holes that may exude sap or sawdust-like excrement to indicate lilac borer infestation.

If borers are caught early, they can be effectively managed by pruning off limbs that are being attacked. This means careful monitoring is key to addressing this pest.

Leafminer

yellow wavy lines on the shrub leaves
Leafminer causes damage to the leaves in the form of yellow wavy lines being larvae.

Most of this pest’s damage is done by its larvae, which are small, white, and less than ¼ inch long. Yellow, squiggly lines (or mines) on your lilac’s leaves will show you where they have been boring through the tissue.

Later in the season, a rolled leaf may indicate that caterpillars are pupating. If leafminers or borers are suspected, prune off affected leaves immediately and keep your eyes peeled for others.

Protect Them During Frosts

frozen shrub in winter
Use a tarp or cloth to protect the lilac from sudden cold snaps.

As cold weather natives, lilacs are not likely to suffer from extreme winter conditions. Their flower buds, however, are susceptible to damage from quick swings in temperature or unusual weather patterns. They require a long, cold, cycle of dormancy in order to flower properly. They can also be negatively affected when a late or early season warm up is followed by a freeze.

In winter, after they have officially entered dormancy, a prolonged warm spell may trigger an early wakeup. You’ll then notice its buds begin to swell. When freezing temperatures return, these buds are often damaged and a poor flower showing is likely to follow.

Likewise, a prolonged, early Spring warmup can also trigger premature bud opening, and these buds can be damaged when freezing temps inevitably return. Petals may be brown and unsightly, or flowers may not open at all.

Keep a tarp or cloth handy to insulate your shrubs during sudden cold snaps and you may be able to prevent bud damage that will decrease bloom production.

Be Patient

Beautiful inflorescences of lilac
In the first season, a freshly planted lilac may not flower, since all its energy will be focused on creating a root system.

It can take a few seasons for newly planted lilacs to deliver an impressive floral display. After being installed, your lilac will focus most of its energy on establishing a vigorous root system, and this will be its priority for at least the first growing season.

On some species, particularly small leaf varieties, you might get a handful of blooms the first year. But full flowering, surface-covering panicles are likely a year or two down the road. Some common lilac varieties may even take 2 or 3 years to fully flower, but it’ll be totally worth it. So be patient.

Final Thoughts

Known for being hardy and low maintenance, lilacs do not require a whole lot of fuss. With routine care, they will live long, healthy lives. Some shrub species are known to live as many as 100 years! This means they have the potential to outlast even the gardener who’s planted them.

They do, however, need to be tweaked and prodded a bit in order to flower plentifully for as many weeks as possible. With proper planting, plenty of sun, good drainage, and faithful pruning, you’ll be giving your lilac the best odds for reaching its flowering potential this season and yourself a front row seat for the show!

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