With green vegetation and large, trumpet-like flowers that come in a range of colours, petunias are a popular annual in many gardens. Requiring little more than occasional watering, petunias are prolific, flowering throughout the spring and summer. While petunias are easy to start from seed, to get genetically identical plants, try rooting cuttings from your favourite petunia. The plants that come from these cuttings will bear exactly the same type of blooms as the parent plant.
Fill a seed tray with a good potting soil mixture. Poke a pencil into the soil in each tray cell to form a hole into which you can place the stem of the cutting.
Cut the ends of petunia stems 7.5 to 10 cm (3 to 4 inches) long and just below a leaf node from mature stems. Remove any leaves within 5 cm (2 inches) of the cut end of the cutting. Remove any blossoms or flower buds from the stems.
Place the cut end of the stems into the rooting compound powder to completely coat the end of each stem. Insert the cut end of each stem into the hole in the potting soil in each cell in the seed tray. Press the soil down firmly around the stem to support the cutting. Water the soil in the seed tray thoroughly so that it is damp, but not wet.
Poke several holes in the large plastic bag to allow excess moisture to escape. Insert the pencil into the centre of the seed tray to hold the plastic bag up from the cuttings. Place the seed tray completely in the bag and seal it.
Place the cuttings in a warm, well lit area away from direct sunlight. Allow the cuttings to remain there for two to four weeks to allow them to root. After that time, check to see if the cuttings have rooted.
Remove the cuttings that have rooted from the seed tray and transplant them to 10 cm (4 inch) grow-out pots filled with top soil. Water them in so the soil is moist. Place the potted plants outside to harden off, before planting them in you your garden.
Newly rooted petunias that were raised indoors do not require any dormancy period before moving outside.