Growing Petunias: A Complete Profile
By Growing Home Greens Team · July 18, 2026
Petunias take the longest lead time of any flower on this list. Seed goes in about 9 weeks before last frost, and it needs light to germinate, so it’s surface-sown rather than buried. That long runway is the price for having sizable, blooming plants ready to set out once the weather turns: a trailing or mounding 6- to 12-inch plant covered in trumpet-shaped flowers across a wide color range.
Surface-sown seed and a long runway
Sow petunia seed on the surface of the mix and don’t cover it. Light is required to germinate. Transplants go out about 2 weeks after last frost, and at one plant per square foot and roughly 70 days to maturity, it behaves like a mid-sized bedding plant. Its low, spreading habit makes it best suited to edges and borders rather than the middle of a bed, where taller vegetables would just shade it out.
A midseason trim, not a sign of trouble
Leggy, sparse petunias partway through the season are normal rather than a sign of trouble, a hard midseason trim (“Chelsea chop” style) encourages fresh, bushier growth and a second flush of bloom. Petunias that never fill in usually didn’t get enough light to germinate in the first place, since the seed needs to stay uncovered and near the surface.
A frame for the bed, not a companion pick
There’s no documented vegetable-companion benefit for petunia in the data behind this site. See the full companion guide for petunias for the full picture. Its low, spreading habit is best used as a border or edging planting in the Garden Designer, framing a bed rather than competing with taller crops for space.
Companion planting guide for Petunia · Find your planting dates
Typically viable in USDA zones 2-11. Not sure your zone? Look it up by ZIP code.
Method: Start indoors: Start indoors from seed, then transplant outside. Petunia needs a head start most zones can't give it by direct-sowing alone.
See exact start-indoors, direct-sow, and harvest dates for your zone →
How many Petunia plants fit per square foot?
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 0.5-1 ft.
Varieties worth considering
- Wave series (including Easy Wave and Shock Wave): Iowa State University Extension groups these under 'spreading' petunias, distinct from upright grandiflora or multiflora types, the right category to look for if you want the low, sprawling edging habit rather than an upright bedding plant. (source)
- Grandiflora types (Dreams, Ultra, Storm series): Iowa State's largest-flowered category, up to 5 inches across on single or double blooms, but the page notes these flower less heavily than other types and hold up poorly in rain, getting straggly by late summer. Choose for the bloom size, not for low maintenance. (source)
- Multiflora types (Celebrity, Carpet, Hurrah series): Smaller flowers than grandiflora but far more of them, and per Iowa State more compact and more weather-resistant, better suited to a mass planting than an individual specimen. The safer choice if petunias in a bed (not a container) need to survive real rain. (source)
Cited from the source shown next to each variety. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement.
Where to buy petunia seeds
As an Amazon Associate we earn from qualifying purchases. Some links on this page also go to other retailers we may earn a commission from as an affiliate, at no extra cost to you. We only recommend products with a genuine consensus of positive, independent reviews. See the sources cited on each item.
See it growing
Search YouTube for "growing petunia" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
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Growing Petunia: A low, spreading border flower started indoors nine weeks ahead of frost, grown for edging appeal, not for any documented vegetable pairing.
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