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How to Grow Petunias in Your Garden: 5 Care Tips for Petunias

Written by MasterClass

Last updated: Jul 17, 2020 • 4 min read

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Planting petunia flowers is an easy way to incorporate explosions of color into your landscape, either in garden beds, or cascading from hanging baskets and window boxes. These popular flowering annuals with cheerful, gramophone-shaped blossoms are among the easiest to grow and maintain.

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4 Petunia Varieties

There are four main types of petunias:

  1. Grandiflora petunias: The oldest variety of the bunch, Grandiflora petunias produce softball-sized blooms in zones with moderate summer temperatures. Their large flowers are striking in hanging baskets, but they can begin to droop mid-season, especially in humid environments.
  2. Multiflora petunias: Multiflora petunias are considerably smaller than Grandifloras, but hardier in more challenging weather, like wind and rain. Their blooms come in both single and double varieties, which take on a crinkled, carnation-esque fullness.
  3. Milliflora petunias: Miliflora petunias are tight, compact plants, with smaller flowers to match. They’re easygoing and low-maintenance when planted in baskets or containers: They bloom quickly, and don’t require any pruning to produce new blooms.
  4. Spreading petunias: Also known as Wave petunias, this variety is an eye-catching choice for ground cover or edging gardens. Varieties like “Tidal Wave” will usually spread up to four feet.

How to Plant Petunia Seeds

Petunias are slow to emerge in the beginning, but once established, are low-maintenance, consistent growers.

  1. Start indoors. To get a head start on planting petunias, start seeds indoors about two months before the last frost date. Fill peat pots with a seed-starting mix (a finer blend of nutrient-dense potting soil available at any garden center or nursery), and place in a tray. Sprinkle petunia seeds over the top of each pot. To sow, gently press petunia seeds into the soil, but do not cover: These sun-loving blooms need light to germinate, too. Mist with a spray bottle, and cover with plastic wrap before setting in a warm, well-lit place like a sunny windowsill (or on a heat mat with a grow light, if full sun is unavailable). Keep the soil moist by pouring water directly into the tray to avoid disturbing the tiny seeds. After 15 days, seedlings should fully sprout. To supercharge their growth before transplanting, stick them under fluorescent lights during the day.
  2. Pick the site. Petunias thrive in direct sunlight, unlike their lookalikes, impatiens flowers. While partial shade can work, aim for a planting site that gets at least six hours of sun per day. Like most plants, petunias need fertile, well-draining soil with a slightly acidic pH—6.0 to 7.0, which is achieved by incorporating organic materials or fertilizer as needed.
  3. Prepare the site. To ensure that the soil has proper ventilation, till organic matter like compost into the first eight inches or so with your hands. Dig holes about the same size of the starter pots before planting.
  4. Plant. Carefully remove the petunia seedlings from their containers, or, as is the norm with many biodegradable seed starter pots, simply place the pot directly into the hole. Fill in with soil, tamping down gently around the delicate stems. Space petunias according to their type: compact Millifloras can be closer together, around six inches, while other petunia types may need around 10 inches, depending on their size. Water well to establish the root systems.
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How to Care for Petunias

Petunias are relatively simple to grow. The colorful flowers require routine watering, pest control, and mulching to thrive.

  1. Water regularly. Petunias have relatively shallow roots, and depending on the container they’re planted in and their sun exposure, some plants may need daily watering. Check the soil and keep an eye on the health of the leaves to determine the right watering schedule for your petunia plants.
  2. Control pests. Aphids are a common petunia pest, especially for young plants; if you notice curling, sickly leaves or spot the clusters of pale green insects, remove the infected leaves, or treat with insecticidal soap. Companion planting offers a chemical-free way to curb the problem.
  3. Mulch. A light layer of soft organic material like straw or grass clippings will regulate the temperature and moisture of the soil and keep weeds from taking hold.
  4. Deadhead. Deadheading is a form of pruning that simply refers to the removal, either by pinching or clipping, of dead flowers to encourage new growth. Some varieties will not require deadheading, but Grandiflora and Multiflora petunias should be regularly deadheaded to maintain appearance and productivity.
  5. Fertilize. Prolific petunia plants benefit from the occasional application of liquid fertilizer, either applied directly to the soil, or sprayed in diluted form over their foliage. Pelleted slow-release fertilizer is another option for plants planted in a soilless growing medium.

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