My Wave Petunias are dying! What's wrong with them?
We recommend that you rotate bed plantings every year and replace the soil in containers. We have found that this simple step minimizes the loss of plants. Wave petunias require at least six hours of full sun to perform at their best.
And Wave Petunias are heavy "feeders"! If possible, mix a tablespoon of dry or slow-release fertilizer with the soil or into the hole when you are planting your Wave Petunias. This will provide constant food as the plant grows. If you are using a standard fertilizer, like Miracle Gro®, try fertilizing twice as often as usual to promote new growth. However, even after increasing the feed, it may take as long as 10 to 14 days to see significant growth throughout.

Also, maintain adequate moisture. The plants should not be so dry that they start to wilt. Wilting is not only a sign of the plant needing water, but can also mean that the roots are dying. The best practice for watering is to test the soil by poking your finger down in the soil at least 2.5 to 3 in. If it's still moist, you do not need to water. During the hottest months of the Summer, you may need to water every day or twice a day for small containers. Check for insect damage. Use the recommended insecticide for the specific pest or another control you prefer.

If you have done all of this and your plants are still not performing well, it may be best to take one of your plants to a local nursery to help determine the possible cause of the problem. You can also contact a Master Gardeners or University/Extension Agent in your area.