The lilac week

Most flowers don't become people. Most don't get bound to a specific human in your memory in the way a song does, or a particular dish, or a kind of soap. But lilacs do. Almost everyone I've ever talked about lilacs with, who has any feeling about them at all, has the same structure of memory — a grandmother, a great-grandmother, a great-aunt, a specific older woman in their family who had a lilac bush, and the smell now belongs to that person, in that yard, in that part of the year. The flower has, in a real and stable way, become a relative.

This is unusual. Roses don't do it. Tulips don't do it. Apple blossoms don't, even though they're seasonally similar and were more agriculturally important. Cherry blossoms have their own intense seasonal recognition but they aren't usually family in the same way. Lilacs are.

This is a post about why.

The species, very briefly

The lilac of family folklore — the dense purple-lavender shrub at the side of an old house — is Syringa vulgaris, the common lilac. It's a deciduous flowering shrub native to the Balkan peninsula and southeastern Europe. It came to North America with European settlers in the late 1700s, became wildly popular as an ornamental on the Atlantic seaboard by 1850, and from there spread westward as the agricultural frontier moved. By 1900 it was the default shrub planted at every farmhouse and rural homestead from Quebec across the prairies to the Pacific coast. It is one of the most reliably hardy woody flowering plants on the continent, surviving down to roughly USDA zone 3 (Calgary's zone), and it lives a long time — fifty to a hundred years isn't unusual, with some heirlooms going past 150.

If your grandmother or great-grandmother had a "lilac in the yard" anywhere in Canada, it was almost certainly S. vulgaris, and the chances are decent it predated her tenancy in the house — these are typically planted by one generation and inherited by two or three more.

The Canadian innovation

There's a specific Canadian footnote worth knowing. In the 1920s, a horticulturist named Isabella Preston was working at the Central Experimental Farm in Ottawa, breeding ornamental plants suited to the brutal Canadian climate. She crossed S. villosa (a hardy late-blooming Chinese species) with S. reflexa (also Chinese), producing a hybrid called Syringa × prestoniae — the Preston lilac.

Prestons bloom two to three weeks later than common lilac. The reason this matters in practice is the late-spring frost: in a typical Calgary or Edmonton year, the standard S. vulgaris sets buds in early May and is vulnerable to a final cold snap that can blacken the entire annual bloom. The Preston hybrids miss that frost window by blooming late enough that it's already June. They're widely planted across the prairies; many of the lilacs older Canadians remember from childhood are actually Prestons rather than vulgaris, blooming a little later, in slightly different colours (pinker, sometimes magenta, less of the pale-purple classic).

Isabella Preston produced about 75 hybrids during her career and is one of the most successful women in the history of plant breeding. The Preston lilac is the second-most-common lilac in Canada, and the most distinctively Canadian flower we've contributed to global horticulture.

Why lilacs become people

The mechanism, I think, has three pieces.

Short, intense bloom. A lilac's flowering window is short — eight to fourteen days, total. The smell goes from absent to overwhelming to gone in less than two weeks. Anything seasonally rare and chemically intense ends up encoding into autobiographical memory more readily than something that's around all summer.

Distinctive smell, with a name. Lilac has a chemical signature dominated by the molecules α-terpineol and cis-3-hexenyl acetate (from leaf-volatile lineage) plus a set of related floral esters. The result is so distinctive and so widely-recognized that "lilac" is a perfumery note in its own right — the way "rose" or "vanilla" or "jasmine" is. Most flowers don't get a perfume note. Smell encodes to memory more directly than any other sense; pair a distinctive smell with a brief annual window and you have something that almost has to attach itself to a specific moment.

Yard placement. Lilacs are shrubs, six to fifteen feet tall, planted typically against a house wall or as a hedge near the front porch. They grow exactly where a small child would walk past them on the way out the door, eye-height to waist-height for most of childhood. The bloom happens at the start of summer break — the moment of the year when grandparents are visited, when porches are reoccupied, when a kid is set loose in a yard. The combination of physical geometry, calendar timing, and family-visit pattern means that a lilac bush is, for many people, the first powerful smell ever encountered in association with a beloved older relative.

Roses don't have this. They're usually back in flowerbeds, planted by adults, encountered as a managed garden rather than a side-of-house ambush. Cherry blossoms are above your head. Apple blossoms happen in orchards, not yards. Lilacs are at the door, at the right height, at the right time of year, with an unforgettable smell. The architecture of memory has very little to do with you.

What Toronto plants on its streets

The species your grandmother had — S. vulgaris — is essentially absent from Toronto's street-tree inventory. The city has 18,677 catalogued lilacs in the road allowance, but 17,589 of them are Syringa reticulata, the Japanese tree lilac — a different species entirely, native to Japan and northeastern Asia, growing as a small tree (8–10 m) rather than a shrub.

Tree lilac blooms three to four weeks later than common lilac (mid-to-late June rather than mid-to-late May), and the flowers are creamy white panicles, not purple. The smell is also different: more privet-like and honey-adjacent, missing the high-floral terpineol notes that make common lilac instantly recognizable. It's a perfectly fine tree, and a sensible choice for a street boulevard — but it isn't your grandmother's lilac. It's a cousin, at most.

The reason common lilac isn't on the city's planting list is structural. Toronto plants street trees — single-trunk, vertical-axis, prunable to a clear stem above sidewalk height. Common lilac is a multi-stemmed shrub that wants to spread laterally; you can shape it to a single trunk with effort, but it fights you, and the natural form is incompatible with a 2-metre boulevard alongside pedestrians. So common lilac stays in private yards and the occasional park edge — exactly the places it's been for a hundred and fifty years.

Where to find them, this year

If you want to be surrounded by vulgaris bloom in southern Ontario, the destination is the Royal Botanical Gardens in Burlington — specifically the Katie Osborne Lilac Dell in the Arboretum. It's one of the largest documented lilac collections in the world, with over 700 cultivars across the genus including a near-complete representation of Preston hybrids.

Closer to home, the Toronto Botanical Garden at Edwards Gardens has a smaller but real lilac collection. Mount Pleasant Cemetery has scattered specimens. Several of the older-grid neighbourhoods on this site — Cabbagetown, the Annex, Leaside — have private-yard lilacs in front gardens that you can smell in passing on a late-May walk. The bloom is so brief and so widely-staged that if you make a single Saturday-afternoon walk through any old residential neighbourhood between May 18 and 25, you'll catch it.

The foundation-marker thing

One last thing. If you ever drive across the prairies in late May or early June and notice clumps of lilac bloom in the middle of empty fields — purple, lavender, white, pink — those are almost always old farmsteads. The houses are gone. The fences are gone. The driveway has been ploughed under for fifty years. But the lilac was planted in 1910 by someone's grandmother against the south wall of the house, and it survived the abandonment, and it's still blooming on the same calendar day it bloomed when the house had a roof. There are entire prairie counties where you can map the locations of vanished farms by satellite imagery, looking for lilac clumps where the sectional grids show no current building.

This is the most literal version of the metaphor we started with. The flower outlives the family that planted it. The smell that became a person, eventually, becomes a marker for a person who is no longer there. Your great-grandmother's lilac in Calgary may or may not still be physically standing — depends entirely on what's happened to the house. But the species, somewhere on the same prairie, in some abandoned yard a half-mile up the road, is almost certainly still doing exactly the same thing she watched it do, every single year.

It is one of the more durable monuments people accidentally build.

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