Last Updated on October 24, 2022 by Plant Mom Care
Petunia, a genus with 20 species and numerous hybrids, is indigenous to South America. These tender perennials are mainly grown from hybrids these days. They are abundant bloomers and can be found in almost every color except true blue.
Their wide, cone-shaped flowers grow on branching hairy, and slightly sticky foliage. The plants vary according to the variety, with some having double blooms, smooth or ruffled petals, veined, striped or solid colors, cascading or mounding growing habits, and some with fragrance and some without.
They are fast-growers and reach full size towards the end of spring. Their sizes also vary from 6 – 18 inches tall and spread on the ground from 18 inches – 4 feet. In cold areas, they are annuals and will only last one season. In warmer climates, they will return every year although they won’t last long—three years at most. They will self-seed for continuous growth.
Planting petunias hinges on the last predicted frost – these plants should not be exposed to frost. Plants must be spaced about a foot apart. They will keep flowering all summer if given enough water, sun, and fertilizer.
Petunias Light Requirements
Most varieties like growing under full sun, with a minimum of 6 hours of the full sun almost every day. But they will benefit from partial shade in hot summer to keep them blooming better.
They don’t like to stay dry for too long. They also don’t like water-logged soil, which could bring root rot. Too much water can also make them leggy with less flower production. Make sure the soil is well-draining – potted plant containers should have plenty of drainage holes.
Generally, it’s enough to water bedded plants deeply once a week – although spreading varieties and potted plants need deep and frequent watering, as often as twice daily in very hot weather. Don’t let the topsoil dry more than 2 inches.
They prefer low to moderate humidity levels to thrive while high humidity will delay flower production.
They prefer temperatures around 60 – 75°F during the day and 55 – 65°F at night. They can tolerate low temperatures around 40°F, but frost or freezing temperatures will cause damage and eventually kill the plants.
They prefer light, fertile, and slightly acidic soil with good drainage. They are tolerant of different soil types if they are well-draining.
Repot the plant in spring when temperatures are warm and all danger from frost has lessened. Use a bigger pot than the one you used before and add a 1-inch layer of charcoal or gravel in the pot first to help water drain away faster. Now add potting soil and fill 1/2 of the pot. Make a depression about the same as the plant’s root ball in the soil.
Carefully ease the plant from the old pot and tease the roots apart. Settle the root ball into the depression and hold the plant in place while you add soil to completely cover the roots. Keep adding soil until the soil is roughly 2 inches from the lip.
Make sure the stems are above the soil. Place the pot under a light shade, moving it under the full sun when the plant gets adjusted to the new pot.
These plants can be propagated from cuttings and seeds. Propagation from cuttings is better to continue growing the original variety as seeds will not grow the same as the original plant, often taking the color of one of the original plants it was bred from.
Gardeners frequently use cuttings to save a particular variety—particularly if it’s difficult to find at local nurseries.
Take cuttings from healthy stems in autumn before any frost. Trim off healthy portions from stems that are around 6-inch long. Go for supple green stems over older and woody stems.
Remove foliage from the lower part of the stems. Put them in little containers filled with moistened moss or coco peat and place them under indirect bright light after dipping their ends in rooting powder. Keep them lightly watered, and roots will develop within a few weeks. When a couple of true leaves appear, transfer the new plants into the garden or larger individual containers.
Propagation from Seed
Young plants are usually bought from a nursery but it can be a good challenge to try and grow petunias from seeds. Start the seeds 2 months before spring. Spread the tiny seeds on a tray of the damp seed-starting mix. Gently tamp them down, but do not cover them as light is needed for the germination process.
Cover the tray with plastic film and move it to a warm area under indirect light. Germination should start within 7 – 10 days. Remove the plastic and transfer them into individual pots when three true leaves emerge. When more foliage appears, it can be transferred to the garden or in larger pots.
Feed these plants when you first plant them with balanced fertilizer – you can also add some compost to the soil, then from July until the plants start declining in autumn, fertilize them every 2 – 3 weeks with a fertilizer specifically for flowering plants.
When planting young plants, pinch back the tips to encourage branching. Deadhead blooms and trim back leggy growth in midsummer to encourage healthy fresh growth, more branching, and flowers.
To create a fuller and larger appearance, plants grown in pots can be positioned a little closer to one another than in flower beds. But don’t plant more than 3 plants in a 12- inch wide and deep container and the container should have plenty of drainage holes.
Petunias Common Problems
A few pests like flea beetles, aphids, slugs, and snails might attack the plant and feed on the foliage. Sometimes they can just be washed off the plants using a strong spray of water. But in severe infestations, you can use neem oil or insecticidal soap and spray the plant to get rid of these pests, repeating the treatment after 2 weeks.
These plants can be prone to fungal diseases like gray mold, particularly in rainy weather or humid conditions. Remove affected foliage and use a fungicide in severe cases.
There are several causes for wilting flowers or leaves, but most come down to too much/too little water. Inspect the topsoil – if it’s dry, water the plant. If it’s moist, reduce watering.
These plants often develop leggy foliage, but this is easy to correct – deadhead flowers frequently and pinch the stems. As the foliage regrows, it will produce more branching and be less leggy.
How to keep petunias flowering longer?
Make sure they get full sun for around 6 hours every day. They produce fewer flowers if they don’t get enough light. Keep the soil constantly moist, but not water-logged. Potted plants might need watering every day or more.
Feed them regularly. In May, feed them every second week, increasing it to once a week in June as the flowering season comes up. Avoid using fertilizers with a high content of nitrogen as it encourages foliar growth rather than flowers. Feed them with either a balanced fertilizer or one that is high in phosphorus.
Prune off 1/3 of the plant. This will encourage branching and flowering or cut just a few branches every week so you don’t affect the flowers all at once. Deadheading spent blooms will also encourage more flower production.
Do petunias return every year?
These plants are perennials however, in cold climates they are usually treated as annuals. In warm climates, they often survive and even flower in winter. In cooler climates, bring the plants indoors in winter.
What month is best to plant petunias?
For ideal outcomes, plant them in late October to early November or in late January to mid-March.
How do I make my petunia bushy?
Make sure they get enough light every day. Pinch back young plants when you plant them to encourage branching and continue pinching back the tips of stems as the plants grow to encourage more branching, water them properly, particularly in summer– do not over- or under-water them.