Ornamental · Solanaceae
Petunia
Petunia × atkinsiana
Give it full sun and steady feeding, and the petunia pours out color from late spring until frost.
Full sun
Every 2–7 days
50–86°F · 10–30°C
70–90 days
Overview
Petunias are the workhorse of the summer flower bed, blooming hard from late spring right up to the first frost. They belong to the nightshade family, the same clan as the tomato and the potato, and have been bred into hundreds of hybrids in nearly every color but true black. You'll find them spilling out of hanging baskets, edging walkways, and filling window boxes wherever a sunny spot needs color.
Most gardeners meet petunias as one of four broad types. The old Grandifloras carry the showiest, largest flowers, the Multifloras trade size for weather-tough abundance, the tiny Millifloras stay neat and compact, and the spreading Wave types sprawl across beds and baskets while cleaning up after themselves. Knowing which one you've got tells you how much deadheading and pinching it will ask of you.
They are easy to please but hungry. Give them full sun, rich soil, and a steady supply of food and water, and they reward you with months of bloom. Skip the feeding or let a container bake dry, and you'll see leggy stems and a thin scatter of flowers instead.
Care
The short version: full sun, evenly moist but never soggy soil, and regular feeding, since petunias are heavy feeders that flower hardest when they're well fed and well watered.
Light
Petunias bloom best in full sun, ideally six or more hours a day. They'll take a little partial sun, but in too much shade the plants stretch, flop, and give you far fewer flowers.
Water
Keep the soil evenly moist but never soggy, letting the top inch begin to dry between waterings. Containers and hanging baskets dry out fast and may need daily watering in summer heat, so check them often. Soggy, poorly drained sites invite rot, so drainage matters as much as moisture.
Soil
Plant in well-drained, fertile loam rich in organic matter. A pH between 6.0 and 7.0 suits them, and good drainage keeps the roots healthy through a wet spell.
Temperature
Petunias grow well across a wide band, roughly 50°F to 86°F (10°C to 30°C). They thrive in summer warmth but won't survive frost, which is why they're grown as annuals in cold-winter climates.
Humidity
Average humidity around 40% to 60% is all they ask. More important than the number is airflow, since still, damp air around crowded plants is what lets gray mold get going.
Feeding
Petunias are heavy feeders, especially in pots, so feed every two weeks through the growing season. A balanced water-soluble fertilizer from spring to fall keeps the flowers coming instead of petering out by midsummer.
Pruning
Pinch young plants to push them to branch, and deadhead spent blooms on older Grandiflora and Multiflora types to keep them reblooming. Cut leggy stems back by about half in midsummer to freshen the plant, though spreading and Wave types are self-cleaning and rarely need it.
Repotting
Container petunias are usually replanted each year rather than kept on. Watch for roots circling the pot or poking through the drainage holes, fast wilting between waterings, and stalled growth with fewer flowers, all signs the plant has outgrown its space.
Size & spacing
Plants stand 6 to 12 inches (15 to 30 cm) tall and spread 12 to 35 inches (30 to 90 cm) wide depending on the type. Give the spreading kinds room to run and the airflow keeps disease down.
When to plant
Petunias need warmth and have no tolerance for frost. Start the fine seed indoors 10 to 12 weeks before your last spring frost, then set the plants out once the cold has passed and the soil has warmed, and they'll bloom from late spring through fall until frost ends the show.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 10 to 12 weeks before the last spring frost
- Plant: after the last spring frost when soil has warmed
- Harvest: late spring through fall until frost
Troubleshooting
Most petunia trouble shows up on the flowers and the soft new growth, where pests gather and rot takes hold. Catch these early and a quick response keeps a small problem from spreading. Match what you see below, then act while it still helps.
Sudden wilting with dark, mushy roots
When a petunia wilts, yellows, and folds despite moist soil, root and crown rot from overwatering is the usual culprit. Lift the plant and feel the roots: healthy ones are firm and white, while rotted tissue is brown, soft, and foul. There's no saving a badly rotted plant, so discard it, fix the drainage, and let the soil dry a little between waterings on the survivors.
Fix:
- Remove and discard severely affected plants
- Improve soil drainage and reduce watering frequency
- Replant in well-drained soil or containers with drainage holes
Chewed buds and ragged petals with dark specks inside
This is the work of budworms, the larvae of the tobacco or geranium budworm moth that tunnel straight into developing buds. Check the buds at dusk for small green, tan, or reddish caterpillars and the gritty frass they leave behind. Handpick what you find, strip off the ruined buds, and treat young larvae with Bacillus thuringiensis before they bore in deep.
Fix:
- Handpick and destroy larvae
- Remove and dispose of infested buds
- Apply Bacillus thuringiensis (Bt) or another labeled product targeting young larvae
Silvery stippling on leaves and twisted, off-color blooms
Thrips rasp at foliage and flowers, leaving a silvery sheen, black fecal flecks, and warped petals in their wake. Tap a bloom over white paper and watch for the slim pale or dark insects that drop out. Pull the worst flowers, treat with insecticidal soap, and reach for reflective mulch or sticky traps, since thrips also carry viruses from plant to plant.
Fix:
- Remove heavily infested blooms and debris
- Apply insecticidal soap or a labeled insecticide
- Use reflective mulch or sticky traps to reduce populations
Fuzzy gray mold on spent flowers and leaves
Botrytis blight, also called gray mold, settles onto fading blooms and crowded foliage when the weather turns cool and damp. Look for grayish, fuzzy spore masses on rotting tissue during humid spells. Clear away the infected flowers and leaves, open the planting up for airflow, and water at the base so the foliage stays dry.
Fix:
- Remove and dispose of infected flowers and leaves
- Improve air circulation and spacing
- Water at the base and avoid wetting foliage
Curled new growth coated in sticky honeydew
Colonies of aphids cluster on tender shoot tips and leaf undersides, sucking sap and leaving a sticky film behind. Knock them off with a sharp jet of water, then follow up with insecticidal soap or horticultural oil where they cling. Lady beetles and other predators do plenty of the work for you, so go easy on broad sprays.
Fix:
- Spray plants with a strong stream of water to dislodge aphids
- Apply insecticidal soap or horticultural oil to affected growth
- Encourage natural predators such as lady beetles
Toxicity
Good news for pet owners: petunias are safe. The ASPCA lists them as non-toxic to cats, dogs, and horses, and they pose no real poisoning risk to other animals or to people. The most a curious nibble might bring is a brief, mild stomach upset.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Petunia is listed as non-toxic to cats, so a curious nibble is no cause for alarm. A cat that eats a lot of any plant might get a brief upset stomach, nothing more.
Dogs None
Dogs can chew the leaves or flowers without poisoning risk. The most you might see is mild, passing tummy trouble if one eats a large mouthful.
Horses Safe
Horses are not poisoned by petunias, which the ASPCA clears as safe alongside cats and dogs. Grazing on a few blooms causes no expected harm.
Rabbits Safe
Rabbits can browse petunia foliage and flowers without toxic effects. As with any rich treat, sudden large amounts may loosen the gut, so keep portions modest.
Livestock Safe
Cattle, goats, and sheep face no poisoning danger from petunias. The plant simply isn't a toxic threat to grazing animals.
Birds Safe
Petunias hold no known toxin for pet or backyard birds. A bird that pecks at a bloom is in no danger.
People Safe
Petunias are not poisonous to people, so an accidental taste by a child is nothing to worry about. The plant is grown for color, not the table, so there's no reason to eat it.
No special handling precautions for toxicity are needed, though ingestion of any plant material may cause mild, transient stomach upset in sensitive animals.
Varieties
Petunias come in hundreds of named hybrids, but they fall into four broad groups that decide a plant's flower size, weather toughness, and habit. These are the ones worth knowing.
Grandiflora
Carries the biggest blooms of any petunia, up to 4 to 5 inches across, though those large flowers bruise easily in rain and heavy weather.
Multiflora
Trades size for numbers, holding many smaller flowers that shrug off rain and rough weather far better than the Grandifloras.
Milliflora
The miniature of the group, with tidy 1 to 1.5 inch flowers on neat, compact plants.
Spreading/Wave
Low, trailing types that spread wide across beds and baskets and clean themselves, so deadheading is barely needed.
How to propagate
You can grow petunias from their tiny seed or take cuttings to copy a plant you already like. Seed gives you the most variety, while cuttings clone a favorite exactly.
SeedModerate
Germination in about 7 to 14 days; bloom roughly 70 to 90 days from sowing
Start petunias from seed about 10 to 12 weeks before your last frost, scattering the dust-fine seed on the surface of moist seed-starting mix. Don't cover it, since the seed needs light to sprout, and keep the mix warm and damp until it germinates in roughly 7 to 14 days. The seedlings are slow at first and reach bloom around 70 to 90 days from sowing, so move them outside only once the frost has passed and the soil has warmed.
Stem cuttingsModerate
Roots typically form in about 2 to 3 weeks
You can also clone a favorite plant from cuttings. Snip 3 to 4 inch tips from healthy, non-flowering stems, strip the lower leaves, and push them into a moist, well-drained rooting mix. Keep them warm and humid and roots usually form in about 2 to 3 weeks, at which point you can pot each cutting up.
Myths
Petunias are poisonous to cats and dogs.
This one isn't true. The ASPCA lists petunia as non-toxic to cats, dogs, and horses, so a nibble won't poison a pet. A big mouthful might cause a brief stomach upset, but that's the worst of it.
Every petunia needs constant deadheading to keep blooming.
It depends on the type you're growing. Older Grandiflora and Multiflora petunias do rebloom better when you pluck the spent flowers. Modern spreading and Wave types are self-cleaning and need little to no deadheading at all.
Petunias are true annuals that live only one season by nature.
By nature they're tender perennials. Gardeners in temperate climates grow them as annuals only because frost kills them. Given a frost-free spot, the same plant can carry on past a single season.