How to Grow Petunias
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Knowing how to grow petunias comes down to light, drainage and steady, practical care. The three extension guides below agree that petunias need a sunny spot, soil that drains well, and water given deeply rather than in small splashes. They differ on feeding schedules, pinching and the timing of planting, so this guide shows where each source stands.
Petunias suit beds, containers, hanging baskets and window boxes. The sections below cover light and soil, plant types, starting plants, spacing, watering, feeding, deadheading and common problems, and each point names the page behind it.
Quick answer
- Give petunias full sun, or at least five or six hours of good light, in soil that drains well.
- Water thoroughly, with 1 to 2 inches every seven to 10 days once plants are established, and avoid frequent light sprinkling.
- Deadhead large-flowered and double types, since many smaller-flowered cultivars clean themselves.
- Feed with a balanced fertilizer at planting, then keep feeding through the season on the schedule your source gives.
Choose full sun and soil that drains
Light comes first. Minnesota Extension calls it the most important requirement, noting that petunias need at least five or six hours of good sunlight. Clemson HGIC is just as direct: petunias “will become spindly and have few flowers if grown in shade.” UF/IFAS says petunias grow best in full sun and in well-drained soil that is kept moist.
Soil matters less for fertility than for drainage. Minnesota Extension says soil “needn’t be terribly rich” but that it “must drain decently,” and it recommends working in organic matter. The page says to “Spread the organic matter 2 to 3 inches thick” and to “Incorporate it into the soil to a depth of 8 to 10 inches,” using a rototiller or garden fork. Clemson adds that the best growth comes in well-drained, light soil of medium fertility, with a pH of 6.0 to 7.0. If the soil or the area is poorly drained, Clemson suggests building raised beds.
Pick a petunia type that fits the space
The sources sort petunias into groups by flower size and habit. Minnesota Extension says that “Grandiflora have the largest flowers,” while “Multiflora have greater numbers of somewhat smaller flowers.” Millifloras are the miniature group, and spreading types, such as the wave petunias, are fast growers that fill large spaces. Clemson’s list for South Carolina is narrower: “The types of petunias best suited to growing in South Carolina are the multifloras, millifloras and spreading petunias.” It says grandifloras “generally do not thrive” there, because their heavy blossoms are prone to damage and rot in hot, humid summers.
Plant height also varies. UF/IFAS notes that “Some petunias will only grow to be about 6 inches tall while others can get over a foot tall,” and that spread can run from about 18 inches to as much as 4 feet, depending on the variety. For a container, pick a compact type. For a groundcover, pick a spreader and give it room.
Containers call for a little more attention. Minnesota Extension says containers need timed-release fertilizer worked into the soil, and that hanging baskets may need water as often as daily. For ideas on plantings that suit small spaces, see self-watering window box planters or hanging planters for outdoor use.
Start from young plants or from seed
Most home gardeners buy young plants, and Clemson HGIC gives a simple test: “Purchase healthy young petunias that are short and compact.” It adds that “Leggy, thin plants are slow to adjust to outdoor conditions.” Clemson also says plants should be hardened off before they go into exposed beds, which means a few days in a sheltered spot first.
Seed is more work. Minnesota Extension says that “it takes 10 to 12 weeks before petunias are big enough to plant out,” so indoor sowing starts early. Petunia seed is very fine and “they also need light in order to germinate,” so it should be sprinkled on the surface, not covered. The page suggests a warm spot of 70 to 85 degrees Fahrenheit, with seedlings usually appearing in “7 to 10 days after planting.” Clemson gives a shorter head start of eight to 10 weeks before planting in beds.
The timing outdoors depends on where you live. Minnesota Extension says to wait until “soil warms to about 60 degrees Fahrenheit and frost danger has passed.” Clemson says to plant once the danger of frost is past in spring. UF/IFAS takes a different view because it writes for Florida, saying “In Florida, October and November are the best time to plant petunias.” The UF page is written for Florida gardens, so a northern gardener should not copy its calendar.
Space plants and decide whether to pinch
Spacing depends on the type you choose. The table below shows what each source says, along with its advice on pinching.
| Source | Spacing in the source | Pinching advice |
|---|---|---|
| Minnesota Extension | Grandiflora and multiflora about 12 inches apart in full sun; millifloras as close as 4 to 6 inches; spreading types at least 1 1/2 feet apart | Pinch grandifloras and multifloras back when they are about six inches tall; do not pinch millifloras or spreading types |
| Clemson HGIC | 12 to 18 inches apart for groundcover | Pinch off the top inch before planting to encourage good branching |
| UF/IFAS Gardening Solutions | 12 to 18 inches apart if planting as a groundcover | Pinch off the top inch of the plant to encourage branching |
The pinching advice does not agree. Clemson and UF/IFAS both say to pinch the top inch, while Minnesota Extension says to wait until the plant is about six inches tall and to leave millifloras and spreading types alone. This guide shows both approaches rather than picking one. Minnesota Extension also says that petunias planted in containers should go much more closely together, and the sources give no number for that spacing.
Water deeply, and not too often
UF/IFAS says petunias should get “at least 1 to 2 inches of water every 7 to 10 days once established.” Clemson gives the same benchmark and warns against “frequent light watering that encourages shallow rooting.” Minnesota Extension frames the same idea in a different way. It says that “thorough watering once a week should be sufficient in all but the worst weather,” and it notes that spreading types need more frequent watering.
The Minnesota page also says to “soak the soil to a depth of 6 to 8 inches every time you water” when using sprinklers. Shallow sprinkling does little for a plant whose roots need to go down, so the goal is a long soak rather than a quick wet top layer. Hanging baskets and window boxes dry out faster, so check them more often.
Wet leaves invite trouble. UF/IFAS warns that petal blight can be a problem in rainy and very humid weather, and it advises that you “avoid getting leaves or flowers wet when watering.” Clemson gives the same advice, saying to avoid wetting the foliage and flowers to help prevent disease.
Feed on a schedule that matches the season
Feeding is where the three pages differ most. Minnesota Extension gives the most detail. When planting a bed, it says to “work a balanced fertilizer such as 8-8-8, 10-10-10, or 12-12-12 into soil at a rate of 2 pounds per 100 square feet.” It then says, “Later, early to mid-July, begin to use liquid fertilizer every 3 weeks,” and notes that spreading types “require weekly fertilizing.”
UF/IFAS and Clemson HGIC both take a simpler line. UF/IFAS says “Fertilize your petunias monthly with a balanced fertilizer,” and it also names controlled-release products for planting time, which this guide does not repeat. Clemson says to “Fertilize petunias monthly with a balanced fertilizer to support their rapid growth and heavy blooming.” The gap between a monthly feed and a liquid feed every three weeks is real, and the sources do not reconcile it. A soil test, which Minnesota Extension recommends, is the best way to settle the question for your own bed.
Deadhead, and prune when plants get leggy
Deadheading keeps petunias blooming. UF/IFAS says that “Deadheading is necessary on large-flowered and double petunias while many of the smaller flowered cultivars are self-cleaning.” Clemson says the same, and adds that “Many of the smaller-flowered cultivars are self-cleaning.” Minnesota Extension recommends removing faded flowers along with the portion below each bloom, since seeds form there and removing them encourages blooming.
Some petunias get leggy. Clemson advises that “If plants become leggy or stop flowering, prune the shoots back to about half their length.” It then says to fertilize with a liquid feed and water well to force out new growth and flowers. Pinching the top inch of young plants, covered in the spacing section, is the earlier step that encourages branching.
Seed from petunias is not a reliable way to keep a favorite. Clemson says petunias “often reseed in the garden, but will not return true to type,” usually reverting to a mix of small white, lavender and rose flowers.
Watch for pests, disease and weather
Petunias have few serious pests. UF/IFAS says so directly, and it adds that aphids and caterpillars may be an occasional problem. Clemson lists aphids and viruses as the usual issues. Keeping foliage dry when you water is the main cultural step that both UF/IFAS and Clemson describe.
Weather creates the biggest risks. UF/IFAS says that “Gardeners in North Florida may have to protect their petunias from frost,” and Minnesota Extension says to give young transplants some shade for a few days at transplanting time when the weather is hot or windy. Both pages are about protecting plants from conditions, not treating them with products.
Frequently asked questions
Do petunias need full sun?
Yes, for the best show. Minnesota Extension says petunias need at least five or six hours of good sunlight, and that the more shade they get, the fewer flowers they produce. Clemson says they will become spindly in shade. Impatiens, which Minnesota Extension names as a better choice for shady places, are the better pick for that situation.
Can petunias be started from seed at home?
Yes, but it takes patience. Minnesota Extension says seedlings take 10 to 12 weeks to reach a size that can go outdoors, and the seed needs light to germinate. Clemson suggests starting seed eight to 10 weeks before planting in beds. Minnesota Extension says to keep the seed warm under clear plastic until it sprouts, and Clemson notes that the seed needs light, so it should not be buried.
How much water do petunias need?
Once established, most sources point to 1 to 2 inches every seven to 10 days, which UF/IFAS and Clemson both give. Minnesota Extension describes a thorough weekly watering that soaks the soil to 6 to 8 inches, and it says containers may need water far more often.
Should petunias be deadheaded?
If they are large-flowered or double, yes. UF/IFAS and Clemson both say those types need deadheading, while many smaller-flowered types clean themselves. Minnesota Extension recommends removing faded flowers and the part below each bloom, because that stops seed forming and keeps the plant blooming.
Will petunias come back next year?
The sources treat petunias as annuals. Minnesota Extension calls them “among the most popular flowering annuals,” and Clemson says they often reseed but do not come back true to type. The pages do not say how a petunia would overwinter in any region, so this guide does not promise a return.
How we chose
We opened three petunia pages from university extension sites on 2026-10-23: UF/IFAS Gardening Solutions, Minnesota Extension and Clemson HGIC. We kept a claim only when one of these pages states it in plain words, and we show the figures each page gives. Where the pages disagree on pinching, watering frequency or feeding, we show each view and do not choose between them. Where a page is written for one state, such as Florida or South Carolina, we say so. The only arithmetic in this guide is the reading of spacing ranges into the table above.
What we could not verify
The three pages leave several gaps, and this section names them so you can plan around them.
What the sources do not say
- The sources do not give a planting window for every region. UF/IFAS gives October and November for Florida, and Clemson says its recommendations are for South Carolina conditions and “may not apply to other areas.”
- No page gives a spacing for petunias in containers, although Minnesota Extension says they go closer together there.
- The pages do not agree on how often to feed. The monthly schedule and the every-three-weeks schedule are both in print, and this guide does not decide between them.
- None of the pages says how long a planted petunia lasts through the season in a given zone.
- The Clemson page names control products for slugs and aphids. This guide does not repeat them, because treatment advice is outside what it covers.
The three pages were written for three different climates: Florida, South Carolina and Minnesota. A grower elsewhere should check local planting dates with a county extension office, since the sources themselves send readers there.
Bottom line
Give petunias full sun and well-drained soil, water them deeply about once a week, and deadhead the large-flowered types. Feed on the schedule your own soil test suggests.
Sources
- https://gardeningsolutions.ifas.ufl.edu/plants/ornamentals/petunias/ (opened 2026-10-23)
- https://extension.umn.edu/node/9061 (opened 2026-10-23)
- https://hgic.clemson.edu/factsheet/petunia/ (opened 2026-10-23)
