How to Grow Petunias
Petunia × atkinsiana
The most-planted annual in America — cascading color in sun from late spring until frost.
By the Plants by Zone Editorial Team · Reviewed June 1, 2026
About petunias
Petunias are the go-to annual for reliable, nonstop color in beds, borders, and hanging baskets from late spring through frost. Modern trailing types like the Wave series virtually eliminate the need for deadheading, while large-flowered grandifloras reward a little pinching with spectacular blooms. A few hours of full sun, regular feeding, and occasional shearing are all they ask in return for months of color in nearly every shade except true blue.
When to plant and harvest petunias
Timing is relative to your frost dates. Find your USDA zone for exact dates, or browse the month-by-month calendars.
Start seeds indoors
10–12 weeks before last frost
Transplant outdoors
After last frost, once nights stay above 50°F
Direct sow
Not recommended — the seed is dust-fine and difficult to manage outdoors
Harvest
N/A — deadhead or shear for continuous color
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How to grow petunias step by step
- 1
Start from transplants (far easier) or surface-sow seed on moist mix under bright light 10–12 weeks before last frost — do not cover the dust-fine seed.
- 2
Pinch seedlings above the third leaf pair before transplanting to force bushy, branching growth.
- 3
Set out after the last frost in full sun and well-drained soil, spacing mounding types 12–18 in and trailing types 18–24 in.
- 4
Feed every 1–2 weeks with a balanced water-soluble fertilizer — petunias are heavy feeders that stop blooming without regular nutrition.
- 5
Deadhead spent grandiflora blooms; shear trailing multiflora and Wave types back by one-third midseason when they get leggy, and they'll flush fresh in 2–3 weeks.
- 6
In the hottest climates, afternoon shade preserves flower color and prevents the leggy sparse growth that sustained heat brings.
Common problems growing petunias
⚠ Leggy, bare-stemmed plants with few flowers
Shear plants back by one-third to one-half in midsummer — they recover in 2–3 weeks with a dense flush of new bloom.
⚠ Tobacco budworm (holes chewed in buds and blooms)
The most common petunia pest: green or brown larvae bore into buds at night. Apply Bt or spinosad at dusk weekly during the egg-laying season — budworms are resistant to most other insecticides.
⚠ Yellowing leaves
Usually overwatering plus poor drainage, or iron deficiency from high-pH soil. Improve drainage, check pH, and switch to a fertilizer with chelated iron.
⚠ Gray mold (botrytis) on spent blooms
Deadhead regularly, space plants for airflow, and water at the base so foliage stays dry.
✗ Keep away from
🧺 Harvesting petunias
Petunias are a display plant rather than a cut flower, but short stems work in mixed arrangements for a day or two. To keep plants blooming, remove spent grandiflora flowers by pinching just below the old bloom. Multiflora and trailing Wave types are more self-cleaning but still respond dramatically to a hard midseason shearing — cut them back by a third, water well, and they return with weeks of fresh, compact bloom.
Petunias: frequently asked questions
When should you plant petunias?＋
In most regions you start seeds indoors 10–12 weeks before last frost, then transplant after last frost, once nights stay above 50°F. Timing is relative to your last frost, so find your USDA hardiness zone for the exact planting dates where you live.
Why do my petunias get leggy and stop blooming in summer?＋
Petunias naturally stretch and tire in peak heat. Cut them back by one-third to one-half around midsummer, water and feed well, and they flush a whole new round of compact blooms as the weather moderates.
What is the difference between grandiflora, multiflora, and Wave petunias?＋
Grandifloras have the largest individual flowers but need the most deadheading. Multifloras bear smaller blooms but are more prolific and self-cleaning. Wave and other trailing types are spreading, ground-cover forms bred for containers and mass planting with minimal maintenance.
Sources & review
Written and maintained by the Plants by Zone Editorial Team. Planting times are based on USDA hardiness zones and NOAA frost-date normals, with care guidance drawn from Cooperative Extension sources. Last reviewed June 1, 2026.
USDA Plant Hardiness Zone MapNOAA U.S. climate normalsCooperative Extension
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