Long-blooming, deer-resistant, and available in almost every colour, petunias are the most popular bedding plant in the world. I love picking up a few plants that catch my eye at the garden centre in spring, but it’s also fun to grow uncommon petunias from seed.
The tiny seeds are strong germinators, but the seedlings need a long head start, as in 10 weeks from seed to transplanting. You also will need supplemental light. I use the same fluorescent fixture I will use later in the spring for starting tomatoes.
The parent species of modern petunias are native to South America, and were introduced to the gardening world in the 1820s. Backyard gardeners loved how the pest-resistant flowers perfumed the evening air, which won the coarse, sticky plants a place in many gardens. Several wild species were intensely hybridised for decades, resulting in two heritage petunia varieties developed a century ago that are still available today.
I first saw ‘Old Fashioned Vining’ petunia in a church garden where it had grown for years. Growing to 24 inches (61cm) tall, the rangy plants continue to bloom well into autumn, and shed a generous crop of seeds. The hundred-year-old ‘Balcony’ variety has a similar upright growth habit, which becomes more relaxed and vinelike as the plants age.
Fragrant Petunias for Pots
Petunias emit fragrance at dusk to attract the attention of night-flying moths, their preferred pollinators. Indigenous South American people thought the scent of petunias helped ward off evil spirits, and I agree that catching a sniff of the flowers’ sweet floral perfume feels like a blessing.
For years flower breeders placed priority on petunia colour, such that many of today’s showiest petunias are fragrant only by accident. This is not the case with lilac blue ‘Evening Scentsation’, which is reliably fragrant during late afternoon and evening, and is best grown in pots stationed at nose level.
If you are looking for fragrant petunias in other colours, the best strategy is to visit a garden centre in the evening and give various selections a sniff. Expect no aroma during the early hours of the day, because petunias have strong circadian rhythms.
Pricey Premium Petunias
There is much to love about heavy-blooming ‘Wave’ petunias, except perhaps their price. Super-vigorous ‘Wave’ petunias will form billowing clouds or carpets of color when kept fed and watered. I am especially fond of the ‘Silver Tidal Wave’ variety, an All-America Selections winner from 2002, because it goes with everything and has noticeable evening fragrance. The seeds are not cheap, but neither are the plants, which makes them well worth growing from seed. The same is true of ‘Kabloom’ calibrachoa, a hugely popular mini-petunia for containers.
In mild winter climates, container-grown plants of these and other premium petunias can be trimmed back to 6 inches (15cm) in autumn, and held through winter in a semi-dormant state in an unheated garage or other protected space where they will not freeze. When the plants start regrowing in spring, you can root 4-inch long (10cm) stems in moist seed starting mix to quickly increase your supply of plants.
Growing Petunias from Seed
Petunia seeds are tiny, but seeds of elite strains are often sold in pelleted form, which makes them easier to handle. Pelleted or plain, sow petunia seeds by gently pressing them into moist seed-starting mix. Then sprinkle on more mix until the seeds are barely covered. Kept warm and moist, the seeds usually germinate within 7 days.
Treat petunia seedlings as if they were tiny tomatoes or any other Solanaceae cousin. Move them to roomier pots as needed, and take some time with the hardening off process. Set the plants out after your last frost date in rich, well-drained soil or roomy containers. In midsummer, perk up tired plants by cutting them back by half and drenching them with a high nitrogen liquid fertiliser.