Question
I have struggled for 5 years to find a hardy flower to put in my flower boxes.  The front of my house has hot afternoon sun, and all my flowers get scorched, even with daily watering.  My spiller and filler are fine, it's the thriller that dies, and thats the most important!  Help!

Answer
I wondered what plants you have tried? Hot sun can be a challenge.
Flax is a standard, (center) with its sword leaves in dramatic colors.
Stipa is a grass that has plumes that turn from green to buff and are about a foot to three feet long. There are many other grasses that are smaller and very nice. Blood grass, and Zebra grass come to mind.
Artemisia is nice for its silver or colorful foliage, but not for the flowers.
For flowers, Cosmos, Wallflower, Yarrow, Canna Lily, Verbascum, Yucca, Asters, Russian Sage, Lavender, Lychnis, Penstemon, Torch Lily, Globe Thistle, and Salvia.
As you can see by the variety of perennials I have listed, there are many that will take the heat and still look great. Some however will need a large container.
For Annuals Zinnias, Marigolds, Clarkia, and Bachelor Button.
A few tips in planting for the heat. Plant deeper. Give the plants a little extra soil over the roots. Plant thick plants that will shade the soil from the sun, to keep it cooler. If possible, try to shade the container, with other containers in a group. Or tuck it behind some furniture, or other container shade, leaving the plants in the sun. This will lower the temperature on the roots and give the flowers plenty of light. Keep the soil moist but be careful not to over water. Let the soil dry a bit before watering to keep the plants from drowning.