Lilac Trees vs. Lilac Shrubs and Bushes: What’s The Difference?
Lilac trees and lilac shrubs are different but share some similarities. But how can you tell the difference between the two? And how exactly do they differ? In this article, certified master gardener Liz Jaros examines lilac trees vs. shrubs, and breaks down how to tell them apart by their appearances, as well as their other differences & similarities.
Ushering in Spring each year with an explosion of sweet scented blooms, lilacs are diverse in form and can grow up to 30 feet tall. Descended from 25+ species and cultivated to produce thousands of unique varieties, lilacs can have dense branch structures, small leaves, and uniform bloom patterns.
Or they can be loose and wild, with arching stems and whimsical floral displays. They might also be tall and single trunked with a wide canopy and large, heart-shaped leaves. So how can you tell the difference between a lilac shrub/bush and a tree? With the term ‘tree’ typically reserved for woody plants that grow taller than 15 feet, you might assume that large lilac varieties are trees and small lilac varieties are shrubs.
And to some extent, you’d be right. But the lilac genus (particularly its species with a tendency to soar and sprawl) makes things a bit more complicated than that. In this article, we’ll look at the traditional characteristics of both trees and shrubs. We will then determine how these categories are best applied to the lilacs we see most often in the landscape.
About Lilac Trees
When trying to determine if lilacs are trees or shrubs, it’s important to note that there is no strict scientific or botanical definition for the word ‘tree.’ For classification and communication purposes, a plant is considered a tree if it has a single trunk, a height of at least 15 feet, and a well-defined canopy that begins at least 3-4 feet above ground.
Taking the definition a bit farther, a tree is typically supported by wood that is dead on the interior. It’s then lives and photosynthesizes toward its exterior, with an outer layer of protective bark.
For the lilac genus, this category is expanded to include woody plants with multiple trunks of roughly equal girth. And it really applies to only one species; the Japanese Tree lilac. It also applies to its subspecies; the Chinese and the Amur tree lilacs. Since they are all different in profile, let’s look at the defining characteristics of each.
Japanese Tree Lilac
Packing a wallop in the Spring landscape with clusters of fragrant (sometimes overpowering or off-putting), This tree’s white flowers are 10 inches wide and up to a foot long. This species can also be either single and multi-stemmed. With an attractive shape, reddish bark, and white trunk speckles, Japanese tree lilacs can reach heights of 30 feet and spreads of 15-20 feet. They offer four-season interest, and are equally at home in the city, on a small property, or on the rambling grounds of a grand estate.
‘Ivory Silk,’ ‘Chantilly Lace,’ and ‘Summer Snow’ are the Japanese Tree cultivars most commonly used in contemporary landscape design.
Chinese Tree Lilac
Syringa reticulata subsp. pekinensis
Also early summer bloomers, Chinese tree lilacs send out yellow-white, honey scented flower clusters en masse. Smaller in size at 10-20 feet high and 10-15 feet wide, with a more delicate leaf and branch structure, this species is often selected for its unusual bark characteristics and winter interest. Its cinnamon to amber colored bark exfoliates in sheets and peels later in the season.
‘Beijing Gold,’ ‘Summer Charm,’ and ‘Yellow Fragrance’ are popular Chinese Tree Lilac cultivars.
Amur Tree Lilac
Syringa reticulata subs. amurensis
This subspecies is native to Korea and eastern Russia. It maxes out at 8 feet tall and 6 feet wide, making it an exception to the 15-foot height rule. Its structure and lineage put it squarely in the tree category, but its habit is rounded and more shrub-like than the other tree lilacs.
Amur is a popular choice for small properties and parks. Its flower panicles are white and prolific in early summer with a pleasant scent. Amur has no direct cultivars.
About Lilac Shrubs
Now that we’ve examined some members of the lilac tree family, let’s contrast them with some lilac shrubs to help illuminate the difference.
Traditionally, a shrub is defined as a multi-stemmed, woody plant that is round in form and low to the ground. It should have branch diameters of less than 3 inches. A shrub is also typically assumed to be smaller than a tree. This characterization will apply to most shrubs we see in the landscape.
With lilacs, however, especially members of the common lilac family (syringa vulgaris) which can soar to heights of 20 feet, the lines can get a little blurry. But yes, these towering easy-to-grow woody plants are still considered shrubs.
The biggest distinction between a lilac tree with multiple trunks and a lilac shrub is that multi-stemmed (often referred to as ‘clump’ form) trees will feature trunks that are roughly equal to one another in width. Conversely, shrubs will have stems of varying sizes and thickness with many smaller branches, suckers, and offshoots.
Additionally, lilac trees will have a clearance between the soil and the canopy where there is no side branching. Shrubs will have growth extending from points all along the stems, beginning at ground level.
An exception to this rule is lilac shrubs that have had lower growth pruned off to create a more ‘tree-like’ form. Look for wounds on the lower third of stems to help determine if you might be mistaking a groomed shrub for a tree.
Since lilac shrubs descend from three main species (as well as their hybrids and cultivars), a closer examination of each category can help boost your lilac shrub identification skills. Here are some of their defining characteristics.
Common or French Lilac
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 and widths of 20 feet if left unchecked, common lilacs typically feature smooth, heart shaped leaves and traditional, cone-shaped blooms that are very fragrant.
‘Sensation,’ ‘Beauty of Moscow,’ ‘Charles Joly,’ and ‘Miss Canada’ are just a few of the common lilac varieties you’ll encounter in residential and municipal landscapes. This particular lilac is a popular choice for containers.
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. ‘Red Pixie,’ ‘Lemon Daddy,’ and ‘Superba’ are all popular cultivars.
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, and leaves are narrow. It takes shearing well and is commonly used as a low hedge. All persian lilacs are hybrids of ‘Laciniata’ and ‘Afghanica’ species. There are no direct cultivars but it comes in several colors.
What’s a Shrub Tree?
Okay, here’s where things get really confusing. You’ve probably seen dwarf lilac ‘trees’ in the landscape that look like lollipops. They feature compact balls of leaves and blooms on top of small, single trunks and are often called ‘dwarf trees,’ but they are actually shrubs that have been grafted onto small tree root stock.
So are these lilacs trees or shrubs? I guess they’re a little of both. But the nursery catalogs list them in the shrub section under a ‘dwarf on standard’ subhead, so let’s go with the shrub.
All of the varieties you’ll encounter in the landscape will descend from either ‘meyeri’ or ‘palibin’ species, which feature small leaves and compact form. Some of the most popular lilacs on standard include ‘Miss Kim,’ ‘Tinkerbelle,’ and ‘Dwarf Korean.’
Frequently Asked Questions
Is a bush the same thing as a shrub?
Horticulturally speaking, the words are interchangeable and there is no difference. Casually speaking, ‘bush’ is often used to describe a multi-stemmed woody plant that is unpruned and unbridled, while ‘shrub’ is typically used to describe a multi-stemmed woody plant that is groomed and controlled.
Will lilac trees or bushes bloom longer?
They both bloom about the same duration. There’s no difference in bloom time based on the distinction of tree or shrub.
Will lilac trees or shrubs grow in the shade?
In their native hardiness zones, both lilac trees and shrubs prefer full sun. They can grow in partial sun, but they may not bloom as much as a result.
If you don’t let the common lilac’s extreme height throw you off or the shrub on standard’s unusual stature trick you into thinking it’s a dwarf tree, you should now be able to stroll through the lilacs with a better grasp on the difference between tree and shrub. You might even be able to identify which lilac tree species you have planted in your front yard. You may also be able to kindly correct your neighbor when she shows you her dwarf lilac ‘tree.’
Again, look for growth near the base and a rounded shape to identify a lilac shrub and a single or equal-stemmed trunk beneath an elevated canopy to identify a tree. With these things in mind, you’ll be able to apply this new botanical knowledge to other plants that blur the boundaries between tree and shrub as well.