When midsummer's heat waves leave so many annuals struggling to bloom, Wave Petunias (Petunia x hybrida 'Wave') cool things down with floods of flowers. Ball Horticultural's 'Purple Wave' (Petunia x hybrida 'Purple Wave') appeared in 1992, the first of a series of ground-covering Waves. Perennial in U. S. Department of Agriculture plant hardiness zones 10 through 11, they bloom nonstop from spring to fall's first frost everywhere else. With the right care, they're true showstoppers.
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For strong roots, lush leaves and countless flowers, start Wave petunias off with granulated, slow-release 14-14-14 fertilizer immediately after planting. Spread 3 tablespoons -- or the label's recommended amount -- of the granules over every 4 square feet of soil; work it lightly into the surface and water thoroughly.
Follow with weekly doses of 10-10-10 , water-soluble fertilizer. One manufacturer, for example, requires mixing 6 tablespoons of its fertilizer in 1 gallon of water for each 10 square feet of soil. Your brand may have different instructions, and those are the ones to follow.
Waves need lots of water. Check daily by inserting a finger into the top 2 1/2 to 3 inches of soil. If it feels dry, lift the lower stems and water around the bases of the plants. Otherwise, the flowers and leaves -- not the roots -- get wet.
Water enough to soak the top 6 to 8 inches of soil. If necessary, stop periodically and allow moisture to penetrate its surface.
Pinch Back Sparingly
Wave petunias grow outward, with new stems constantly emerging from their crowns. When the lower stems begin losing leaves and flowers, new ones cover them, keeping the plants fresh and full. Unless they're outgrowing their boundaries, pinching Waves back for tidiness isn't necessary.
- Wave petunias that don't receive enough water or fertilizer can become long and lanky and require pruning back. Using sterilized pruners, trim off several inches of the long stems and begin fertilizing the plant. The petunia should start to recover and resume normal growth within two weeks.
- Sterilize pruning tools by wiping the blades off with alcohol and allowing them to dry before using.
Monitor for Pests
Wave petunias's most serious diseases are insect-vectored viruses. Their most common insect pests are as follows:
- Aphids: Large aphid colonies drain sap from the new stems and leaves, covering the plants with gooey excrement called honeydew.
- Thrips: Slow-flying thrips cause silver or brown scarring on the leaves and flowers, and pepper their feeding sites with black waste.
- Variegated cutworms: These night-feeding moth larvae chew irregular holes in the leaves.
Remove light aphid and thrips infestations by pruning the affected stems and disposing of them in sealed plastic bags. Follow up with organic, ready-to-use insecticidal soap to suffocate larvae you may have missed.
Search petunias with a flashlight after dark for cutworms and drown them in soapy water. If that's not effective, try organic, ready-to-use spinosad spray. Use these sprays in calm conditions, when the temperature is below 90 degrees Fahrenheit and the weather is expected to remain dry for at least 24 hours. Coat petunias until all their surfaces -- including the stems and both sides of the leaves -- drip.
Respray weekly or as often as the products' labels indicate until the aphids and thrips are gone or the worms have stopped hatching.
Organic insecticides minimize the threat to wasps, lady beetles, lacewings and other beneficial bugs that prey on pests.
Spray in the early morning, late evening or at night so insecticides don't harm foraging honeybees.
Wear protective clothing, waterproof gloves, a face mask and safety glasses and follow all the label's instructions when using pesticides.