Answer: Coneflowers are drought and heat tolerant, but only when planted in the ground or a large planter, where they have access to more resources from a bigger volume of soil. It may have died because of the drastic change of conditions - from very dry to wet and hot. Too much water can cause a plant to wilt as quickly as too little, since the roots cease to function when there's so little air in the soil - they literally drown. The plant may have been better off watered lightly in the evening, and perhaps the next evening as well. If your coneflower was standing amidst other plants at the nursery, they were probably keeping one another cool with shared shade, whereas the lone coneflower on the deck had no protection from the heat. If you want to experiment, cut it back to the ground, place it in partial shade and see if it will rise from the dead! Best of luck!
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