Last summer, at the Montreal Botanical Garden, I saw a petunia that was totally new to me. With an erect growth habit and small red star-shaped flowers, it only vaguely resembled the blowzy hybrid petunias (Petunia x atkinsoniana) that I knew. The label gave its name as Petunia exserta. So that solved part of the mystery: it wasn’t some new hybrid, it was a species.
While taking photos with my cellphone, a ruby-throated hummingbird* (Archilochus colubris) buzzed into view and began methodically visiting the flowers, one after the other. I found that odd, because in my experience, hummingbirds usually don’t spend much time visiting hybrid petunias as they’re rather stingy with their nectar. I was intrigued!
*Hummingbirds are found only in the Americas.
A Little Research
Back home, I did a bit of research on this plant and discovered that it’s known to be a hummingbird plant. In fact, it is the only petunia that is pollinated only by hummingbirds in the wild (the others are pollinated by bees and moths). Moreover, it has heavily modified its morphology to please its pollen carrier, developing a red corolla (the hummingbird’s favorite color), an abundance of flowers over a long period and a long tube rich in nectar. The flowers are odorless, though, because hummingbirds are not attracted to perfume.
Note that P. exserta is also the only wild petunia with red flowers. (The others have white, pink or purple flowers.) Interestingly, the red coloration now found in many hybrid petunias comes from very different pigments from those found in this wild species.
The name “exserta” comes from the fact the stamens and stigma that emerge from the corolla, as exserta means “pushed forward.” It’s yet another a specific adaptation to hummingbird pollination. As the hummingbird’s beak dives into the bottom of the flower in search of nectar, its neck rubs against the exserted stamens and picks up pollen that the bird will carry to the next flower. A perfect symbiosis!
Barely Discovered, Already Threatened!
This species was only recently discovered in the Serras de Sudeste of Brazil in 1987 and, sadly, is already considered to be near extinction in the wild. An expedition in 2007 to the cliff side where it grows could only find 14 specimens!
For once, this plant is not threatened by habitat destruction due to farming or urbanization—at least not yet!—but by the intrusion into its territory of another petunia, P. axillaris, a moth-pollinated, night-scented white petunia, one of the parent species of the hybrid petunia. It seems that the two cross quite readily and that the hybrids lose their hummingbird-magnet features.
Grow Your Own
Despite its rarity in the wild, Petunia exserta is not difficult to cultivate. Just treat it like any petunia. Sow the seeds indoors about 10 weeks before the planned planting date in the garden, pressing the seeds into the potting soil without covering them, as they need light to germinate. The seeds will sprout in about ten days at room temperature.
When the soil has warmed up and there is no risk of frost, transplant the seedlings into a bed or container. Petunia exserta prefers full sun and a rich and well-drained soil.
In regions with long a growing season, like southern California, you can skip all the “starting indoors” stuff and just sow it outdoors where you want to see it bloom.
On its own, it’s a rather tallish petunia (18 inches/45 cm) and a bit scrawny: it will look best either grown in a large clusters or mixed in with other annuals.
In addition to hummingbirds, butterflies love it. On the other hand, the sticky texture of its leaves displeases mammals, so deer, rabbits, marmots and their annoying little friends tend to leave it alone.
Where to Find It?
This plant is very new to the market. Just a year or two ago, the only way to obtain was to know a botanist … and not just any botanist, either! It was very, very hard to come by! Lately, a few—very few—seed companies have taken it up and now “share it with the masses” (that means, you and I!). I’ve seen it at Select Seeds in the US, Gardens North in Canada and Plant World Seeds. There may well be a few others.
And if you’re looking for packs of plants already started and ready for you to plant up … well, be patient. I don’t think you’ll find it in your local garden center anytime soon!
Petunia exserta: beautiful flowers that attract hummingbirds. Certainly a plant worth discovering!
Any advice on thinning seedlings after sowing indoors? Tiny seeds so lots of seedlings. Do you know if they mind being planted out in little clumps?
Always thin. When they start to touch, to about 1 inch if you want to keep a lot, 2 inches if not. At 1 inch, you may need to thin a second time (when they start to touch) if the weather isn’t appropriate to planting out.
Any idea on the spacing when planting these?
About 8 inches (20 cm).