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Petunias - The Classic Annual Flower, Petunia, Gets a Makeover

How to Grow Petunias that Will Bloom All Summer

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Purple Petunias

You can get almost any color flower and many bold combinations.

Photo: © Marie Iannotti

Overview: Petunias are one of the most popular bedding flowers. They have wide trumpet shaped flowers and branching foliage that is hairy and somewhat sticky. They are prolific bloomers, although some forms require deadheading to keep them going. Most varieties will bloom throughout the summer, except in extreme heat. You can now find petunias in just about every color but true blue and with growing habits that mound in borders or trail down containers.

Description: Petunias are annual flowering plants, native to Argentina. Within the petunia family is great variety: single and double blooms, ruffled or smooth petals, striped, veined or solid colors, mounding and cascading habits and even some fragrance. Most of the petunias sold today are hybrids, developed for specific design purposes.

The 2 oldest types of petunias are grandifloras and multifloras. Both are somewhat mounding. Grandiflora has larger flowers, but Multiflora holds up better in the rain. If you grew petunias a few decades ago, you will remember how the flowers turned to mush, when they got wet.

Spreading type petunias, which include The ‘Wave’, ‘Supertunia’, ‘Cascadia’ and ‘Surfinia’ series are some of the most popular petunias because most don’t need deadheading and they can be used as bedding plants, ground covers or trailing in containers.

‘Calibrachoa’ or ‘Million Bells’ look like tiny petunias, but they are actually an entirely different species.

Trying to categorize petunias by looking at them is difficult, but it’s hard to go wrong with the varieties currently being sold. Hopefully your petunias will be labeled. Look for the traits you most value: flower size, flower abundance, no deadheading required... You should be able to find a suitable petunia in what ever color you choose. Here are examples of each of the types listed above.

Botanical Name: Petunia X hybrida

Common Name: Petunia

USDA Zone: Although some species of petunia are tropical perennials, today’s hybrids are usually grown as annuals.

Exposure: Most varieties prefer full sun, but in the heat of mid-summer, partial shade will be appreciated.

Bloom Period: Repeat blooms throughout the summer. Some varieties will require frequent deadheading and some pruning back to continue setting flower buds. Extreme heat can cause petunia plants to stop setting flowers until the temperature drops.

Growing Notes: Petunias do best in full sun, but can handle partial shade, especially in hotter areas. They are very slow to grow from seed. If starting from seed, begin at least 10 to 12 weeks before planting out date.

Petunia seed needs light to germinate, so don’t cover the seed. Sprinkle it on top of the soil and pat lightly, for good contact. They also prefer warmer temperatures for germination. Start the seeds on heating pads or on top of your refrigerator. Once the seed has germinated, move them from the warm area and let them grow on in cooler temperatures.

Although petunias like cool weather, they are not frost tolerant. Wait until all danger of frost is past before planting your petunias outdoors.

When planting, pinch the seedling back to encourage more branching and a fuller plant. How far back to pinch depends on the plant. If it is a short, stocky seeding, just pinch and inch or less. If the seedling has gotten gangly, you can pinch back by half.

Petunias will tolerate a range of soil pH. They don’t like to be dry for long periods, but they also don’t like wet feet.

Maintenance: Older varieties of petunias require diligent deadheading or they will stop blooming. This is not always a pleasant task, since the foliage is sticky and blossoms that have been rained on turn to slimy mush.

Even the newer varieties that say they don’t require deadheading will benefit from a pinching or shearing mid-season. When the branches start to get long and you can see where all the previous flowers were along the stem, it’s time to cut them back and refresh the plant.

Monthly feeding or foliage feeding will give your petunias the energy to stay in bloom. But be judicious with water and make sure the soil is well drained. Too much water will cause the plants to become ‘leggy’, with lots of stem and few flowers.

Problems: Petunias are usually carefree growers although they can get pummeled by rain.

  • Gray Mold and Soft Rot - Usually occurs in rainy climates. Choose weather resistant varieties.

  • Aphids - Hose off with a strong blast of water.

  • Budworm caterpillar - Small green caterpillars that attack late June and July and feed on the flower buds. Often you won’t see the actual caterpillar, but you may notice small black dropping and small holes in the leaves and buds. They’ll disappear in July, but you could use Bt on them, if it’s a real problem.
  • Design Suggestions: Because of their profuse blooms, petunias are excellent in hanging baskets, either alone or as a trailing plant in a mixed planting. They are low growing and need to be planted in large groupings, to make a splash in the garden. But containers of petunias can be placed in strategic areas of the garden, to add color where needed.
  • Suggested Varieties: New petunia varieties come out every year, making older varieties obsolete, but hear are some particular favorites.
    • ’Blue Spark’ Cascadia - Trailing violet flowers with a sweet scent.
    • ‘Supertunia Silver’ - White with lavender throat and veins. Good weather tolerance and very floriferous.
    • ‘Prism Sunshine’ - AAS winning hybrid with buttery yellow grandiflora sized flowers with multiflora weather tolerance. Can be grown from seed.
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