Scented petunias

Someone has been fooling around with the petunia genes and it could be a good thing. Petunias in my garden last summer were puffing out a heady scent after dusk from their long tube throats, the kind of deep nectar repository hummingbirds look for. I spend quite a bit of time thinking of ways to entice my little hummer to stay longer in the garden, so I’m interested in knowing more about this. Petunias (Petunia x hybrida) are in the Solanaceae family, and related to tobacco and ornamental nicotine (Nicotiana hybrids and species), another flower with a long tube throat and similar scent.

From my completely disorganized survey of petunia scent (which involves sniffing each cultivar as I pass along the nursery aisle), it seems not all petunias are perfumed. This is a highly inaccurate method, because flowers express their perfumes at particular times (often morning or evening) and in certain climate circumstances (high humidity, cool air temperature), and usually smell like nothing at all in mid-day hours at the garden centre. However, it can be said that some petunias are more perfumed than others.

There are many flower sizes, colours, bi-colours and forms of petunias (spreading hedgiflora, grandiflora, multiflora, milliflora, frilled, double). All are bred from two Argentinian species: P. axillaris, with large, highly scented, night-blooming white flowers; and P. integrifolia, with small, almost scentless violet blossoms. These two species have provided ample genetic material for hybridizers to develop a broad colour palette and diverse plant forms. In particular, the breeding work done on spreading petunias (like the Wave, Easy Wave, Tidal Wave, Shock Wave, Avalanche and Ramblin’ Series) allows us to select plants for groundcover in beds, or to cascade down the sides of baskets and containers. And then there are the mounding petunias, in every colour from palest pink to almost true black, with stars, striping, bi-colour veining and multi-colour throats of every kind.

In this plethora of petunias, no catalogue description mentions scent. Most breeding work has focused on colour development and I can say it’s gone way overboard on that, having been startled by some of the garish new cultivars like candy-pink and green ‘Lime Bicolor’. The innovation of self-cleaning plants like Proven Winners’ Supertunia (no more wet tissue paper-type spent blooms) has been useful.

Scent has remained illusive and unpredictable, but there are some worthwhile plants available. The original P. axillaris species can still be grown from seed (anniesannuals.com), and the Tumbelina Mixed Perfume Collection of double flowers has been developed in Britain.

I’ve grown Madness Plum Crazy petunia and it was indeed scented, and perhaps other cultivars with mauve petals bearing purple veining will also have perfume. I know for certain that the yellow and white grandiflora ‘Prism Sunshine’ petunia is deliciously scented at night; and as well, several double petunias (especially mauve-purple cultivars) also are perfumed. Purple Wave also seemed somewhat scented in my garden last summer. Those Argentinian species are floating around in these hybrid plants and the scent genes from P. axillaris seem prominent in white (or white bi-colour), veined mauve single and double purple flowers.

This is not just speculation from a hummer-hopeful gardener. Scientists at the University of Amsterdam have isolated the volatile benzenoid chemicals that synthesize perfume in species petunia petals. It’s known that white P. axillaris emits strong scent after dusk to attract night-flying hawk moths; violet P. integrifolia produces a less intense daytime scent to attract pollinator bees in sunlight. Isolating the scent genes makes it easier to breed new perfumed petunias.

Take no notice if you should see me this spring, sniffing my way down the petunia aisles. I’ll be engaged in serious research!