Ornamental · Solanaceae
Petunia
Petunia × atkinsiana
Give it full sun and steady feeding, and the petunia fires off color from late spring right up to frost.
Full sun
Every 2–7 days
50–86°F · 10–30°C
70–90 days
Overview
Petunias power a summer bed like few other flowers, blazing away from late spring clear through to the first frost. They spring from the nightshade family, the same crew as the tomato and the potato, and breeders have churned out hundreds of hybrids in nearly every color but a true black. Watch them tumble from hanging baskets, chase a walkway edge, and pack out window boxes anywhere a sunny corner begs for a jolt of color.
Most growers latch onto petunias through one of four broad types, and pinning yours down changes the whole game. The old Grandifloras throw the biggest, boldest flowers, the Multifloras trade size for weather-tough numbers, the tiny Millifloras stay neat and compact, and the spreading Wave types race across beds and baskets while tidying up as they go. Nail the type and you already know how much deadheading and pinching lies ahead.
They come easy but they eat like crazy. Hand them full sun, rich soil, and a steady flow of food and water, and they fire back months of nonstop bloom. Skimp on the feeding or let a container bake dry, though, and you land leggy stems and a thin scatter of flowers instead.
Care
The short version: full sun, soil kept evenly moist but never soggy, and regular feeding, since petunias are heavy feeders that bloom flat out when they are well fed and well watered.
Light
Petunias bloom flat out in full sun, ideally six or more hours a day. They will take a little partial sun, but push them into too much shade and the plants stretch, flop, and crank out far fewer flowers.
Water
Keep the soil evenly moist but never soggy, letting the top inch start to dry between waterings. Containers and hanging baskets burn through their moisture fast and may beg for daily watering in summer heat, so check them often. Soggy, poorly drained sites invite rot, so drainage carries just as much weight as moisture.
Soil
Drop them into well-drained, fertile loam loaded with organic matter. A pH between 6.0 and 7.0 hits the sweet spot, and sharp drainage keeps the roots charging through a wet spell.
Temperature
Petunias thrive across a wide band, roughly 50°F to 86°F (10°C to 30°C). They soak up summer warmth but crash at frost, which is exactly why cold-winter climates run them as annuals.
Humidity
Average humidity around 40% to 60% is all they chase, so this one barely registers. What really counts is airflow, since still, damp air around crowded plants hands gray mold its opening.
Feeding
Petunias are heavy feeders, especially in pots, so feed every two weeks through the growing season to keep them roaring. A balanced water-soluble fertilizer from spring to fall keeps the flowers rolling instead of stalling out by midsummer.
Pruning
Pinch young plants to fire up branching, and deadhead the spent blooms on older Grandiflora and Multiflora types to keep them reblooming. Cut leggy stems back by about half in midsummer to jolt the plant, though the self-cleaning spreading and Wave types mostly handle it themselves.
Repotting
Container petunias get replanted each year rather than dragged on. Keep watch for roots circling the pot or shooting through the drainage holes, fast wilting between waterings, and stalled growth with fewer flowers, all shouting that 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. Turn the spreading kinds loose with room to run, and the airflow that follows keeps disease on the back foot.
When to plant
Petunias run on warmth and buckle at the first frost, so timing is where the fun starts. Fire the fine seed indoors 10 to 12 weeks before your last spring frost, then push the plants out once the cold clears and the soil warms, and they will blaze from late spring through fall until frost finally calls it.
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
Petunia trouble almost always breaks out on the flowers and the soft new growth, the exact spots pests crowd and rot grabs hold. Jump on it early and a fast response shuts a small problem down before it runs. Match what you spot below, then move while the fix still lands.
Fast wilting with dark, mushy roots
A petunia that wilts, yellows, and folds while the soil sits wet has almost certainly hit root and crown rot from overwatering. Pop the plant loose and check the roots, since firm and white spells health while brown, soft, and foul spells rot. A badly rotted plant is done, so pull it, sharpen up the drainage, and let the soil dry a little between waterings on the survivors to send them charging back.
Fix:
- Remove and discard severely affected plants
- Improve soil drainage and reduce watering frequency
- Replant in well-drained soil or containers with drainage holes
Bored buds and shredded petals with dark grit
Shredded blooms and dark grit inside them give away budworms, the larvae of the tobacco or geranium budworm moth that tunnel straight into forming buds. Head out at dusk, crack open a few buds, and hunt down the small green, tan, or reddish caterpillars and the frass trailing behind them. Pick every one, strip the wrecked buds, and hit young larvae with Bacillus thuringiensis before they burrow in and the flowers bounce right back.
Fix:
- Handpick and destroy larvae
- Remove and dispose of infested buds
- Apply Bacillus thuringiensis (Bt) or another labeled product targeting young larvae
Silvery stippling and warped, faded blooms
A silvery sheen, black flecks, and twisted petals flag thrips, slim insects that rasp away at leaves and flowers. Snap a bloom over white paper and watch the tiny pale or dark specks scatter loose to nail the diagnosis fast. Yank the worst flowers, treat with insecticidal soap, and roll out reflective mulch or sticky traps, since thrips shuttle viruses from plant to plant and stopping their spread pays off.
Fix:
- Remove heavily infested blooms and debris
- Apply insecticidal soap or a labeled insecticide
- Use reflective mulch or sticky traps to reduce populations
Gray fuzz on tired flowers and crowded leaves
Once cool, damp weather rolls in, Botrytis blight, better known as gray mold, moves onto tired blooms and crowded foliage. Scan the rotting tissue during humid stretches for those grayish, fuzzy spore patches. Sweep out the infected flowers and leaves, throw the planting open for airflow, and aim your water low at the base so the foliage dries fast and the mold loses its grip.
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 with a sticky glaze
Curled tips and a sticky glaze on the fresh growth mean aphids have piled onto the shoot ends and leaf undersides, tapping the sap and dropping their residue. Blast them off with a punchy jet of water, then chase the holdouts with insecticidal soap or horticultural oil. Lady beetles and their allies charge in and clear plenty on their own, so ease off the heavy sprays and let the good bugs work.
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
Great news for pet households: petunias are safe. The ASPCA clears 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 stirs up is a brief, mild stomach upset.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Grow petunia freely around a curious cat, since it lands on the non-toxic list. Even a cat that dives into any plant might get a quick upset stomach and nothing worse.
Dogs None
Dogs can chomp the leaves or flowers with zero poisoning risk. The worst a big, greedy mouthful brings is a bit of passing tummy trouble that clears on its own.
Horses Safe
Horses join the safe list too, cleared by the ASPCA right alongside cats and dogs. Let one graze a few blooms and expect no harm at all.
Rabbits Safe
Rabbits can dig into petunia foliage and flowers with no toxic worry. Keep the helpings modest, since any rich treat piled on too fast may loosen the gut.
Livestock Safe
Cattle, goats, and sheep run no poisoning risk from petunias whatsoever. The plant simply packs no toxic punch for grazing animals.
Birds Safe
Petunias carry no known toxin for pet or backyard birds, so let them flit in. A bird that pecks a bloom walks away just fine.
People Safe
Petunias are not poisonous to people, so a child who grabs a taste is perfectly fine. They earn their keep with color rather than flavor, so there is no reason to eat them.
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 all shake out into four broad groups that lock in a plant's flower size, weather toughness, and habit. These are the ones worth chasing down.
Grandiflora
Swings for the biggest blooms of any petunia, hitting 4 to 5 inches across, though those giant petals bruise easily in rain and heavy weather.
Multiflora
Piles on the flower count instead of the size, packing many smaller blooms that shrug off rain and rough weather far better than the Grandifloras.
Milliflora
The pint-sized dynamo of the group, packing dainty 1 to 1.5 inch flowers onto neat, compact plants.
Spreading/Wave
Races low and wide across beds and baskets and cleans itself as it goes, so deadheading barely enters the picture.
How to propagate
Launch petunias from their tiny seed or grab cuttings to copy a plant you already love. Seed hands you the widest variety, while cuttings clone a favorite dead on.
SeedModerate
Germination in about 7 to 14 days; bloom roughly 70 to 90 days from sowing
Kick off petunias from seed about 10 to 12 weeks before your last frost, scattering the dust-fine seed right across moist seed-starting mix. Skip covering it, since the seed needs light to fire up, and hold the mix warm and damp until it breaks through in roughly 7 to 14 days. The seedlings take it slow early on and hit bloom around 70 to 90 days from sowing, so wait for frost to clear and the soil to warm before you send them outdoors.
Stem cuttingsModerate
Roots typically form in about 2 to 3 weeks
Want an exact copy of a favorite plant? Cuttings deliver. Snip 3 to 4 inch tips off healthy, non-flowering stems, strip the lower leaves, and drive them into moist, well-drained rooting mix. Keep them warm and humid, watch roots push out in about 2 to 3 weeks, and pot each cutting up once they do.
Myths
Petunias are poisonous to cats and dogs.
Bust this one wide open. The ASPCA lists petunia as non-toxic to cats, dogs, and horses, so a nibble will not poison a pet. A big mouthful might spark a brief stomach upset, but that is as far as it goes.
Every petunia needs constant deadheading to keep blooming.
It rides entirely on the type you are growing. Older Grandiflora and Multiflora petunias bloom harder once you pluck the spent flowers. Modern spreading and Wave types clean themselves and barely ask for any deadheading at all.
Petunias are true annuals that live only one season by nature.
Not so, since they are tender perennials at heart. Temperate gardeners run them as annuals only because frost cuts the season short. Keep one frost-free and that same plant powers on well past a single season.