Not sure about sand + clay -- I have heard it makes a cement-like soil structure, but I have also read that this is a myth. I think gravel or stones would be better in terms of maximizing drainage though.

Biggest killer for Gaillardia is waterlogged winter soil. I have yet to lose one in my clay soil, but all clays are not created equally. Some drain reasonably well, some do not. I would test this first by putting some water in a 1ft by 1ft hole twice and see how long it takes the water to leave the hole completely the second time. If it is > 1 hr., you have problematic drainage.

Compost will improve the soil structure and aerate the soil and will improve drainage over time if mixed in with the existing soil. Also, make sure you don't have the crowns of the plants too low in the soil such that water pools around them. Never fertilize them either -- they hate it.

One anecdotal reason given for Gallardia's lack of staying power is that they flower themselves to death -- expending all their resources to flower prolifically right through the first frost instead of conserving energy to survive winter. There is no science behind this, just speculation. But, you may want to try cutting your Gaillardia back significantly in early fall, about 4-6 weeks before your first frost to force it to devote energy to strengthening itself to survive winter instead of flowering.

This post was edited by mistascott on Wed, May 15, 13 at 11:59

Here is a fairly good writeup about the clay + sand = cement debate. Turns out, it does if not mixed in the right proportion. I would avoid doing it.

I almost hate to share this with you, Ellen, but I grow these successfully in hard red Alabama clay soil. Some composted wood chips were tilled in originally 8 years ago but that's it. We do maintain a layer of mulch on top. We do not have an irrigation system and any plant we choose must be able to thrive in near xeric conditions.

So, blazing sun, clay soil, no irrigation all seem to work for our Arizona Sun. If I'm not mistaken, the first few plants we planted were from Bluestone, but have added many more that I grew from seed. They bloom the first year from seed.