Petunias can be planted out as soon as the last frost has gone. How To Grow Fibrous-Rooted Begonias From Seed You can sow begonia seeds from January to March under glass, polythene or in a propagator, keeping them at a temperature between 21-24°C (70-75°F). This should be carried out two weeks after potting. 10) Keep the plants regularly watered and feed with a general all-purpose fertiliser. This is a very short list, mainly because petunias are quite companionable plants. The obvious one is to give your plants lots of proper care (more on that below). You can plant these petunias at any time after frost dangers is past and once soil temperatures reach 15.6 degrees Celsius. The seedlings need bright light to grow well. This species features 3 to 4 inch (7.5 to 10 cm.) Although there are about forty species growing in the wild the showy varieties that we grow now are all derived from just two perennial species which grow naturally in Argentina. Planting Petunias Outdoors When youâve moved your seedlings outdoors or purchased your transplants, you should be sure itâs after your last spring frost. Petunia seeds are small but easy to handle. Many excellent petunia varieties can be grown from seed, or you can start with plants grown from rooted cuttings. So that rules out cacti, but most other plants should be great with petunias. Surfinia will require pinching to encourage the right habit and breaks to get a bushy and spreading plant. You can also be quick to pluck off dead or dying flowers to spur the plant to put out more buds. Also, youâll need to make sure the area youâre planting the petunias in has fluffy, well-drained soil; is in full sun (or at least partial sun); and has a soil pH of 6.0-7.0. 9) Petunias are generally pest free but greenfly/aphids can become a problem, in which case use a recommended proprietary brand of insecticide. Best Varieties to Grow New petunia varieties come out every year, making older varieties obsolete, but here are some particular favorites. Spreading petunias may need weekly fertilization, while container-grown plants will respond well to a time-release fertilizer. So itâs best not to grow them with shade loving plants, and plants that prefer arid conditions. Surfinia is responsive to daminozide (B9), which can be sprayed at a rate of 2,500-5,000 ppm. Now if you arenât looking for overall plant lifespan, you can have your petunias bloom longer with a few simple tricks. This has more than likely come about by poor sowing techniques or bad compost rather than poor seed performance. We supply petunias in several plug plant sizes, but thereâs a real sense of satisfaction in growing a show stopping summer display of petunias from seed.. Somewhere along the line, petunias have gained a wrongful reputation of being difficult to grow from seed. Petunias do best in full sun or part shade, and need moderate amounts of water. ... United Kingdom ... along with resistance to mildew. It's preferable to plant in the cooler early summer so the newly planted petunias don't suffer shock from summer heat, but plants kept well watered usually survive the heat with minimal damage. After learning how to plant petunias you can include them in your flower bed and container garden. Four species of petunias include hundreds of cultivars and offer a perfect addition to the home landscape: Grandiflora petunias are the most common type of growing petunias. Most gardeners buy petunias as inexpensive bedding plants, set out in spring as soon as danger of frost has passed. Move the pots into a bright, frost-free light place, keeping them moist but not waterlogged until they are safe to plant out in the garden.