Petunias are a popular annual flower that can add beautiful color to any garden. They are known for their trumpet-shaped blooms that come in a wide variety of colors including purple, pink, red, yellow, white, and blue. Petunias are relatively easy to grow and do well in flower beds as long as you follow some basic guidelines when planting them.
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When to Plant Petunias
Petunias should be planted outdoors after the threat of frost has passed in spring. This is usually late April or May depending on your growing zone. Petunias are cold sensitive annuals that will die if exposed to freezing temperatures. Wait until overnight lows stay above 50 degrees F before transplanting petunias into the garden.
You can get a head start on the growing season by starting petunia seeds indoors 6-8 weeks before the last expected frost. Sow seeds in seed starting mix and keep moist and warm until sprouted. Transplant seedlings into larger containers as they grow. Harden off plants for 7-10 days before transplanting into the flower bed by setting them outdoors in partial shade during the day and bringing back in at night.
Choosing a Location
Petunias need a site with full sun exposure, which means at least 6 hours of direct sunlight per day. Insufficient sunlight will cause them to grow leggy and produce less flowers. Make sure to select a flower bed or border that receives ample sunlight.
The soil should be well-draining but also able to retain some moisture. Rich loam or sandy loam soils amended with compost or peat moss work well for petunias. Avoid planting them in heavy clay soils or areas that collect standing water after rains.
Preparing the Flower Bed
Start preparing the flower bed at least 2-3 weeks before planting. Remove any weeds, rocks or debris from the bed. Loosen the top 6-8 inches of soil with a shovel or garden tiller. Mix in 2-3 inches of compost or other organic material like peat moss or rotted manure.
You can also blend in a general purpose fertilizer at this time following package directions. Till everything to a depth of 8-10 inches. Then rake the bed smooth to create an even planting surface. Petunias like slightly acidic soil with a pH between 5.5-6.5. Test the soil pH and add lime or aluminum sulfate as needed to reach the desired range.
Planting Depth and Spacing
Petunias should be transplanted at the same depth they were growing in their containers or seed trays. Dig holes the width of the root ball and deep enough so the top of the root ball sits level with the surrounding soil. Gently loosen any circling roots before placing the plant in the hole.
Plant petunias 8-12 inches apart in rows spaced 12-18 inches apart. You can also plant in geometric patterns or scatter them throughout the bed. Just make sure there is adequate air circulation between plants. Overcrowding will increase disease and encourage leggy growth as plants compete for light.
Here is a table with recommended planting distances:
| Petunia Type | Between Plants | Between Rows |
|---|---|---|
| Spreading | 12 inches | 18 inches |
| Mounding | 10 inches | 15 inches |
| Trailing/Cascading | 8 inches | 12 inches |
This chart shows the recommended spacing for planting different types of petunias in a flower bed.
Planting and Care Tips
Here are some additional tips for planting petunias successfully:
- Water plants thoroughly after transplanting and mist foliage to reduce transplant shock.
- Sink each plant slightly below soil level to prevent drying out.
- Pinch or snip off any blooms during the first 2 weeks after planting so energy goes to root and foliage growth.
- Cover beds with 2-3 inches of organic mulch like shredded bark to retain moisture and reduce weeds.
- Water petunias when top 1 inch of soil dries out. Avoid overhead watering late in the day.
- Fertilize every 2-3 weeks with a balanced liquid fertilizer according to label rates.
- Remove spent flowers promptly to encourage continuous blooming.
- Stake plants over 12 inches tall to prevent flopping, especially in windy areas.
Common Problems
Here are some potential problems to watch for when growing petunias:
Leggy Growth
If plants become stretched out and weak, it is likely due to insufficient sunlight, overcrowding, or excessive nitrogen fertilizer. Pinch back leggy stems or cut back plants by one third to encourage bushier regrowth.
Wilting
Petunias are prone to wilting on hot days even when soil is moist. Apply mulch to cool roots and water in morning if wilting occurs. Avoid overhead watering which can encourage fungal disease.
Leaf Yellowing
Yellow leaves often indicate overwatering or poorly drained soil. Allow soil to dry between waterings and amend soil with compost to improve drainage.
Few Blooms
Insufficient sunlight, over-fertilization with nitrogen, overcrowding, or improper pinching can cause low bloom. Make sure plants get 6+ hours of direct sun and prune back vigorously.
Insect Pests
Common petunia pests include aphids, spider mites, thrips and caterpillars. Use appropriate organic or chemical pesticides if pests appear and damage foliage or flowers.
Fungal Diseases
Gray mold, leaf spot and powdery mildew are possible. Improve air circulation between plants and avoid wetting foliage to reduce disease. Remove and destroy diseased plant parts.
Overwintering Petunias
Petunias are tender annuals that cannot withstand freezing winter temperatures. However, you can dig up plants in fall and overwinter them indoors in a sunny window to replant the following spring.
Here’s how:
- Lift plants gently from the soil and remove excess dirt from roots.
- Repot in containers using sterile indoor potting mix.
- Trim back stems by one third to reduce transpiration.
- Place in a sunny south-facing window.
- Water sparingly, allowing soil to dry out between waterings.
- Keep plants above 60°F but cool and dry in winter.
- Begin fertilizing in spring as day length increases.
- Acclimate plants to outdoor conditions over 7-10 days before replanting after danger of frost.
This process allows you to overwinter selected petunia plants indoors and replant in the garden the next season.
Choosing Petunia Varieties
There are many great petunia varieties to choose from. Here are some top picks:
Wave Petunias
These trailing petunias bloom profusely all season with a mounding, spreading habit. Good choices include Wave Purple, Pink Wave, Tidal Wave Silver.
Supertunia Petunias
Bred for lush foliage and massive blooms, these make a big visual impact. Try Supertunia Vista Bubblegum or Supertunia Bordeaux.
Surfinia Petunias
This cascading type has unique star-shaped blooms. Surfinia Heavenly Blue and Patio Blue are popular. Grow in hanging baskets.
Double Petunias
These have showy, double flowers and come in many colors. Try Double Cascade Rose Vein or Double Daddy Mix.
Wildflower Petunias
Ideal for natural style gardens, these have simpler, smaller flowers. Search for Wild Rose, Red Pinstripe, and Blue Jeans.
Conclusion
With some planning and proper care, petunias are relatively easy to grow in flower beds for gorgeous summer color. Provide them with full sun, fertile soil, adequate spacing, and consistent watering. Protect from frost and pinch back leggy growth. Deadhead spent blooms and monitor for pests or diseases. Select adapted varieties suited to your climate and garden design. With the right growing conditions, petunias will reward you with months of vibrant blooms.