Petunias are such lovely annuals, with many daily blooms. They come in lots of varieties and colors, which can please anyone's eye.
Petunia is a genus of 35 flowering plants in the Solanaceae family and of South American origin. It is closely related to tobacco, nightshade, tomatoes, cape gooseberries, potatoes and chili peppers. Petunia got its name from the French which assimilated the Tupi-Guarani language word "petun," meaning tobacco. Breeders have made many petunia varieties, which they grouped in a few types: Grandiflora, Multiflora, Wave (Spreading), Supertunia, Cascadia and Surfinia.
Petunia is an herbaceous plant, with hairy stem and leaves. Flowers are tunnel-shaped, with joined petals, like small trumpets. The fruit is a capsule which has many tiny seeds inside. They are good for harvesting when the pods are perfectly dry on the plant.
I fell in love with petunias years ago, when I brought many seeds of several petunia varieties from Mamaia (a Romanian seaside resort), while on vacation with my family. They had beautiful petunia beds all over the resort! I saved them in several packets and sowed all during the following years. I usually sow them in large juice cardboard boxes I save, then divide the seedlings in small plastic pots or in balcony planters, where they have enough space to grow better and faster. Some seedlings grow faster, so those are the first planted in the garden, while the others remain in the pots to grow bigger.
Growing plants from seeds isn't such an easy task (as it seems) because the small seedlings need a special care, until they are big enough to be repotted. Too much water can make them rot and too little water makes them dry out.
Not all petunias need annual sowing. The pink, purple and white Petunia axillaris variety I sowed years ago in my garden, reseeds itself every summer, so I just have to water and, eventually, divide the seedlings. On the other hand, a red Petunia atkinsiana 'Superbissima' doesn't reseed in the garden, and I need to sow it every spring indoors. I don't know whether it is the variety or just the weather conditions in the flower bed (too many plants, too low sunlight) but since the red petunias didn't pop out again the following year, I decided to sow them again.
I plant most of the petunias in the garden, as border plants, but I keep a few for the balcony boxes too. I've realized the petunias are more resistant to heat, wind and to the strong sunlight, than the hanging geraniums, which I've always had on my balcony. The wind always breaks the geraniums' stalks and the heat burns their leaves, not to mention that it stopped them from blooming. That's why I've replaced geraniums with petunias and moved them to a sheltered sill, on the western side of the house, where they are now thriving very well.
I don't need to plant more than three petunia seedlings in each planter because each plant gets that bigger and
bushier as growing and it needs lots of space--almost a third of the box. If I plant more than three, some of the plants won't grow very well because the others will shade them. Their roots grow fast, spreading and filling the box, looking like they've swallowed the soil. The plants spread in all directions and bloom a lot, with many flowers daily. Petunias need regular watering, especially after hot summer days. And if I apply a weekly fertilizer, they grow bigger and bushier, with twice as many flowers. They also need deadheading to stimulate blooming. If the plant isn't feeding the dead flower anymore and forming in a seed pod, it has more energy to start new blooms. The colorful petunia flowers bloomed on my balconies all summer long. By the end of the summer, the plants were hanging out the boxes and full of blooms - and seed pods too. The dry seed pods scatter seeds all over, at the slightest move. Some of the seeds that fell into the balcony box were sprouting at the end of the summer, but I can't keep the small plants growing. It would be weird to have them inside during winter, and anyway, they would grow leggy. The best time to grow petunias in our zone is similar to US Zone 5b, starting the seedlings in February. The seeds were already spread into the planter, which spares me the task of sowing more indoor seeds. How cool is that?
Dozens of tiny seeds scattered from the pods...there must be hundreds of seeds in each planter! I'm sure not all will sprout until winter, and I need at least three seeds in there to sprout in February. As a precaution, I always save a few seed capsules before winter comes. This is best done on a sunny, dry day, when the pods are dry. Before the first frost, I pull all the plants out of the boxes, but keep the soil where the seeds have fallen. I usually deposit the boxes in my conservatory during winter, which is like any other heated room in the house, only it has more windows. I never water the planters before February. Then I start watering every day, so the seeds can sprout. At the same time, I put them in a sunny window to get all the light the small plants need.
I continue regular watering until the petunias grow strong in April or May, when it's time to take them outside.
I have to warn you: if you have a cat, he or she might ruin your seedlings if the box is somewhere within reach. I lost some of the petunia seedlings last spring, because my kitty probably wanted to see what was at the bottom of the box, so she dug a big hole in there, did "something" in it and covered it. I managed to save some of the seedlings in that box, but I already had more than enough of other colors and varieties, in the other two planters, so it wasn't a big loss. I had more varieties, among which several hanging petunias, from the seeds I bought from the nursery.
Now that the summer is gone, it's time to bring all the plants inside and clean off all the balcony boxes. I've stored them in a new shed we have, which will leave me more room for my indoor plants in the conservatory. However, I'll bring the planters back inside in February, when I start watering them. Although I know what petunias grew in each planter, I'm looking forward to see what blooms I'll have next summer. Almost every summer, a surprise petunia--different from the others--pops out in the balcony boxes, possibly brought by the wind from the other planters. But until then, a grey, cold, foggy fall is upon us and soon the freezing winter will come. The balcony boxes are in the shed, holding my little colorful treasure. Sleep well, my precious seeds!
 - https://en.wikipedia.org/wiki/Petunia