Petunia

The heat-loving workhorse of summer color: trumpet blooms by the hundred in beds, pots, and hanging baskets, from tidy mounding types to four-foot spreading Waves.

Buy transplants or start the dust-fine seed very early (it needs light), set out after frost into sun, and pinch for fullness.

Most gardeners grow petunias from transplants, and for good reason: the seed is dust-fine, needs light to germinate, and is slow — you'd start it 10-12 weeks before your last frost under lights, surface-sown and kept warm and humid. The best modern spreading types (Wave, Supertunia, and the vegetative brands) are propagated from cuttings and sold only as plants, so you buy them anyway. Whichever route, set petunias out only after all frost has passed and the soil has warmed — they're frost-tender and heat-loving, and cold checks them.

Give them full sun (at least six hours) for the most bloom, in rich, well-drained soil or good potting mix. Pinch young plants once or twice to build a full, well-branched habit that flowers across its whole surface. Space by type — 8-12 inches for mounding types, much wider for spreaders, which fill a big basket or a yard of ground from a single plant.

Water and feed generously (especially in pots), deadhead the big-flowered types, and shear leggy plants back to renew them.

Petunias are heavy feeders and drinkers, particularly the vigorous spreading types in containers and baskets. Water when the top inch of soil dries — hanging baskets in summer may need it daily — and feed regularly with a bloom fertilizer; a starved, dry petunia goes pale and stops flowering. Full sun and warmth keep them blooming hard.

Two maintenance habits matter. Deadhead the grandiflora and multiflora types — pinch off each faded bloom and the little seed pod behind it, or the plant slows to make seed; milliflora and spreading types are self-cleaning and skip this. And when any petunia gets leggy and bloomed-out in midsummer (they all eventually do), cut it back by about a third and feed it — it looks drastic, but the plant rebounds fuller and fresh-blooming within a week or two. Watch buds for tobacco budworm, the classic petunia pest, and blooms for gray mold in wet spells.

Not a cut flower or food - enjoyed on the plant; a favorite plant can be overwintered as cuttings indoors.

Petunias aren't cut flowers or an edible crop — they're enjoyed growing, in beds, pots, and baskets, so there's nothing to store or preserve from the blooms. Seed saving is impractical for the hybrids that dominate the market (they won't come true, and the vegetative types set little or no seed).

The one thing worth 'storing' is a plant you love. Because petunias are tender perennials, you can take stem cuttings of a favorite spreading variety in late summer, root them, and overwinter the young plants on a bright windowsill or under lights to replant next spring — the standard way growers keep named vegetative selections going, since those can't be grown from seed at all.

Species and open-pollinated types come true from dust-fine surface-sown seed; the vegetative Wave/Supertunia selections are kept only by stem cuttings.

From seed: petunia seed is dust-fine — press it onto the surface of a moist, sterile mix and do not cover it, since it needs light to germinate. Bottom-warmth (70–80°F) and 10–12 weeks indoors before your last frost give transplant-ready plants. Species petunias and old open-pollinated strains come reasonably true from saved seed (let a few flowers ripen their small capsules, then collect the fine seed); most modern F1 hybrids will not — their seedlings scatter back toward the parents, so buy fresh hybrid seed each year if you want the exact variety.

From cuttings: the spreading vegetative selections (Wave, Supertunia, and similar) set little or no viable seed and are propagated only by cuttings. Take 3–4 inch stem tips in late summer, strip the lower leaves, and root them in a light mix on a bright sill or under lights — this is how a favorite basket is carried through winter and multiplied for spring, and the sole way to keep a named vegetative variety going.

Leggy plants and stopped bloom are the big ones (shear and feed); budworm hollows the buds, and heat/rain punish grandifloras.

Long bare stems with flowers only at the tips: the universal petunia complaint — leggy from age, heat, or too little light; cut the plant back by a third and feed, and it rebounds fuller in one to two weeks; pinch early to prevent it. Buds holed and hollowed, never opening, with dark specks (frass): tobacco budworm larvae boring into the buds — inspect at dusk with a flashlight and treat with Bt (Btk); it's the classic petunia pest. Blooms melting in heat and rain, few flowers: you're growing a grandiflora in a tough climate — switch to a multiflora, milliflora, or spreading type, which take heat and rain far better. Pale, poorly blooming plants: hungry and thirsty — feed and water more, especially in pots. Gray fuzzy mold on blooms (botrytis): wet weather — remove affected flowers, improve airflow. Clusters on new growth (aphids) or clouds of tiny white insects (whiteflies): hose off or use insecticidal soap.

Bred from wild South American Petunia species into a global bedding flower, transformed again in the 1990s by the ground-breaking spreading Wave.

The garden petunia (Petunia x hybrida) descends from wild species native to South America, chiefly the small white Petunia axillaris and the purple P. integrifolia, discovered in the early 1800s. The name comes, by way of French, from a Guaraní word for tobacco — a nod to petunia's place in the nightshade family alongside tobacco, tomato, and pepper. Crossed and selected through the 19th and 20th centuries, it became one of the world's most popular bedding annuals, in ever-larger grandiflora forms.

The modern era began in 1995, when Ball Seed introduced the Wave series — the first true spreading, ground-covering petunia grown from seed. These vigorous, self-cleaning, weather-tough 'hedgifloras' bloomed along their whole trailing length and changed what a petunia could do, spawning a wave of vegetative brands (Supertunia and others, propagated from cuttings) that dominate today's baskets and containers. From a modest white South American wildflower, the petunia became the summer color of choice on porches and in parks worldwide.

A heat-loving warm-season annual: one long summer show in the north, and cool-shoulder or winter color in the hottest zones.

Petunias love warmth but can be thinned by extreme heat and humidity. Zones 3-6: a summer annual — set out transplants after frost for a long show from late spring to the first fall freeze, which ends them; full sun and warm soil bring the best bloom. Zones 7-8: long warm seasons suit them, but the muggiest midsummer weeks can slow flowering — choose multiflora, milliflora, or spreading types over heat-sensitive grandifloras, and shear-and-feed at midsummer to renew tired plants. Zones 9-10: plant in late winter or fall and grow through the cooler shoulders; petunias bloom through mild winters here and struggle most in peak summer heat. Zone 11: essentially a cool-season flower, planted fall through winter for bloom ahead of tropical summer. Everywhere, petunias are frost-tender and must be replanted each year (or overwintered as cuttings), and everywhere the right type for the climate matters more than any other single choice.