Most people associate wilting plants with a lack of water, but in the case of petunias, too much water can cause the plants to wilt and die. Counterintuitive? Definitely. But it makes sense when you understand that petunias are drought-tolerant and prefer drier, well-draining soil. "We have hot, dry summers, and people often overdo it with watering," says Ward Upham, a horticulturist with Kansas State University. Soggy soil denies oxygen to the petunias' roots, which leads to root rot and eventually droopy plants that look like they need a drink. To solve this problem, you must adjust your watering habits. Soak your garden beds once a week (the water should penetrate at least 6 to 8 inches into the soil). Apply a mulch such as grass clippings around the plants when you transplant them to prevent evaporation. Plants in containers dry out more quickly than those planted in the ground. You may need to water potted petunias daily, depending on the size of the pot. A good rule of thumb is to water the container when the soil is dry down to your second knuckle. You can help increase the drainage in your flowerbeds by spreading 2 to 3 inches of compost onto the beds and then digging it into the soil to a depth of 8 to 10 inches. To ensure good drainage in containers, use a soilless potting mix and make sure the container has at least one drainage hole, recommends Upham. Following a proper maintenance regimen will keep your petunias looking great all summer. At planting time, mix a balanced, granulated organic fertilizer into your garden and potting soils (follow rate recommendations on the box). After the plants have filled in and are growing vigorously, apply a foliar fertilizer such as diluted fish emulsion every three weeks. Most petunias with large flowers must be deadheaded to ensure continued flowering. The smaller-flowering, spreading types often don't need deadheading. If your plants begin to look straggly in midsummer, cut them back by half to encourage a second flush of growth and blooms, says Upham. For a list of varieties that do well in a prairie climate such as yours, check out the Web site prairiestarflowers.com, which lists the annual flower varieties that perform best in Kansas State University's ongoing variety trials.
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