Growing Petunias

How to Plant, Grow, and Care for Petunias

Garden Petunias

Often grown as annuals, petunias are one of the most popular flowers because of their long flowering period. As with most annuals, they get leggy by midsummer, so you’ll want to prune the shoots back to about half their length. See how to plant and take care of your petunias to keep them blooming.

Pretty petunias are treated as annuals in most areas but also as tender perennials in Zones 9 to 11. The flowers come in many colors and patters, and bloom from spring until frost!

These colorful annuals can really add pop to a front lawn and often used as borders, containers, hanging baskets or even seasonal groundcover. Some even have a slight fragrance.

Height can vary from 6 inches to 18 inches. Spread can be from 18 inches to 4 feet.

Petunias are divided into different groups, mainly based on flower size:

  1. Multiflora petunias are the most durable and prolific. They have smaller, but more abundant flowers and are ideal for summer bedding or in a mixed border (because they are more tolerant to wet weather).
  2. Grandiflora petunias have very large flowers and are best grown in containers or hanging baskets (because they are more susceptible to rain damage). Theese large petunias often do not fare as well in the south because they’re prone to rot during humid, hot summers. 
  3. Floribundas: Floribundas are intermediate between the grandiflora and the multiflora groups. They are free-flowering like the multiflora varieties and produce medium-sized blooms.
  4. Millifloras: Milliflora petunias are much smaller than any other petunias on the market. The flowers are only 1 to 1½ inches wide, but they are prolific and last all season!
  5. Spreading or Trailing Petunias: These are low-growing but spread as much as 3 to 4 feet. They form a beautiful, colorful groundcover because the flowers form along the entire length of each stem. They can be used in window boxes or hanging baskets.

Planting

  • Petunias need full sun or they will become spindly. They don’t tend to flower in the shade.
  • They are quite versatile, growing in different types of soil, but it is important that the soil drains well and doesn’t stay wet.
  • You can grow petunias from seeds, but it is easier to grow them from transplants. If you are going to grow from seeds, start them indoors about 10 weeks before you want to set them outside. Petunia seeds are very small (dust-like!) and needs lots of light in order to germinate. Remember to water them. When the plants have three leaves, you can plant them outside.
  • It’s best to buy young plants from a nursery which often sells petunias in flats. Look for plants that are short and compact, not leggy and not yet blooming and they’ll settle in faster.
  • Plant after the last spring frost. (See your local frost dates) in a place that is sheltered from wind exposure.  Keep well watered.
  • Space the plants about 1 foot apart.
  • If you’re planting petunias in containers, use a soil-less mix.

Care

  • Petunias are tolerant of heat so you don’t have to water them regularly. A thorough watering once a week should be sufficient (unless there are prolonged periods of drought in your area). Avoid watering shallowly as this encourages shallow roots.
  • Note: The spreading types of petunias and those in containers require more frequent watering.
  • Fertilize petunias monthly with a balanced fertilizer to support their rapid growth and heavy blooming. Double-flowered cultivars like a biweekly dose of fertilizer.

Getting Leggy in Midsummer

  • By midsummer, most petunias get leggy, producing blossoms at the tips of long, leafless stems. To keep petunias tidy and flowering, we prune the shoots back to about half their length. This will encourage more branching and flowers.
  • After pruning, fertilize and water the plants well to force out new growth and flowers. The plants may look raggedy at first but they’ll rebound with more color and blooms.
    • Older garden petunia plants can be pruned prune hard (within a few inches of the base) to re-encourage vigor, especially in cooler climates, but keep the remaining leaves.
  • Also, remove faded, old, or dead blossoms to both improve blooms and attractiveness, especially for the larger-flowered petunias. Dead-heading prevents seed pods from competing for the plant’s food supplies. Clippings can be added to a compost pile to be recycled.

Pests/Diseases

Petunias have few serious insect or disease pests. Avoid wetting the foliage and flowers when watering to help prevent disease. 

Recommended Varieties

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Growing Petunias

Botanical Name Petunia
Plant Type Flower
Sun Exposure Full Sun
Soil Type
Soil pH
Bloom Time Spring, Summer, Fall
Flower Color Pink, Purple, Red, White, Yellow
Hardiness Zones
Special Features