Where I live in French Canada, everybody knows what day March 19th is: St. Joseph’s Day. And what do you do on St. Joseph’s Day? Why you sow petunia seeds of course! This is so well known here that petunias are actually call “St. Josephs”. That makes perfect sense: this is smack on the right time of year to sow them indoors in view of planting outdoors in May. And you can do this even if you’re not Roman Catholic!
So, in celebration of St. Joseph’s Day, here are a few fun facts about petunias:
• Although petunias are grown as annuals, they are actually perennials. We treat them as annuals because they don’t survive cold winters.
• Petunias were named for… tobacco. In 1803, the French botanist Antoine Laurent de Jussieu named the genus Petunia because the plant was a close relative of tobacco (Nicotiana tabacum), at that time called “pétun” in France. The word petun itself derives from the name of a Patagonian tribe that smoked tobacco.
• There are twenty petunia species, but only two in were used to create the hybrid petunias (Petunia x atkinsiana) we know today: P. axillaris with white, day-scented blooms, and P. integrifolia, with purple evening-scented ones.
• Originally all petunias were scented. However, as hybridizers worked at creating new colors and forms (double flowers, bicolors, different sized blooms, etc.), they neglected scent and it remains essentially absent from most modern hybrids. However, you’ll find that some white-flowered petunias with a delicious day-time perfume and some purple hybrids that are delightfully scented at night.
• Until the 1950’s, petunias only came in 3 colors: white, shades of pink and shades of purple. The first red petunia was launched in 1953 and yellow followed in 1977. The first black petunia, ‘Black Velvet’, dates only from 2011! The color range is now almost complete: the only shade missing is true blue.
• Petunias are carnivorous: the sticky hairs on their stalks and leaves trap small insects. When the latter die and decay, the plant absorbs the nutrients they contain. They share this trait with other relatives in the Solanaceae family, like tomatoes, potatoes and tobacco.
• The trumpet-shaped flowers of petunias were designed by Mother Nature to attract hummingbirds, butterflies, bees and sphinx moths.
Grow Your Own
You can sow petunias outdoors if you want to, but then they won’t flower until the end of the summer. Sowing them indoors is therefore the preferred method, as it ensures bloom as early as mid-May or June, bloom that will continue throughout the summer.
Petunias are not at all difficult to sow, but the seeds are very fine, like dust, so need just a little special attention.
Start by filling a pot or tray with pre-moistened artificial potting soil. Sprinkle the seeds lightly over the surface of the mix, but don’t cover them with soil. Petunia seeds need light in order to germinate.
Press the seeds lightly onto the soil mix using a small block of wood to ensure they adhere to the soil, then lightly spray with lukewarm water. Cover the container with a dome or a clear plastic bag and place the container in moderate light and fairly warm temperatures: 70-80°F (21-26°C). A spot under a fluorescent lamp would be perfect.
The seeds should sprout in about in 7 to 10 days. When you see tiny little green growths, remove the dome or bag to increase air circulation and give the plants more light: full sun (a south-facing window ledge, for example) would be fine at this stage. Or place them 4 to 6 inches (10 to 15 cm) below a fluorescent lamp set at 12- to 16-hour days. Also, lower the air temperature if possible: cooler air, down to about 60°F (15°C), gives stockier plants.
When the seedlings start to touch, transplant them into individual pots or six-packs. Fertilize them every two weeks with an all-purpose fertilizer and water them when the soil is dry to the touch. For better branching, pinch the stem tips when the plants are about 6 inches (15 cm) in height.
Finally, at the end of May or June, harden the young plants off, putting them outdoors in shade at first, then in stronger and stronger light over a week or so. You can plant them outdoors, either in the garden or in pots, baskets or flower boxes, when the soil temperature reaches about 60°F (15°C).
For good bloom, petunias need full sun, relatively rich soil, and watering when the soil begins to dry. A thorough watering or rainfall once a week is usually sufficient for petunias growing in the garden, but you may have to have to water pot-grown petunias daily when conditions are hot and dry.
Saving Them from the Cold
Most gardeners simply let their petunias freeze in the autumn, but you can also take cuttings and grow them indoors over the winter. Ideally, take your cuttings early, at the end of August, as the cuttings won’t root as readily if you take them after nights start becoming cooler.
Indoors, grow your petunias in as as much light as possible and pinch occasionally to promote branching. By March, your “windowsill petunias” will have many branches you can then clip off and root to produce all the plants you need to fill your pots and summer flowerbeds.