Woolly Yarrow (Achillea tomentosa) Culture

I have tried for 3 years to get Achillea tomentosa to establish here without success. It should work, I do not know what I am doing wrong. Please let me know where it grows in the wild, what its pH requirements are, and if I should use a gravel mulch. I live in Silver City, New Mexico, USA. Elevation is 6,000 feet (2000 meters), it's a zone 7, soil is alkaline and, without amendment, heavy and clay-like.

Achillea tomentosa resents prolonged wetness and will succeed in even very dry, sandy soil. Your heavy clay soil is anything but ideal. I suggest you augment it heavily with sharp sand and raise the planting site over the rest of the flower bed to insure perfect drainage.
It is native to South-Western Europe, from central France and central Italy to Spain. It grows there on dry hills and waste ground.
Authors disagree on its hardiness with some claiming it is hardy into zone 3 while others feel it is only hardy to zone 7. Undoubtedly, individual plants vary in their hardiness and will exhibit their best cold hardiness when grown on the dry side. I have the plant in my zone 4 garden in a rather dry site and it has survived the winters of 1999-2000 (not very cold and little snow) and 2000-2001 ( colder, but with excellent snow cover). The present winter (2001-2002) is almost over and has been very mild and dry, so it will not be a test winter either and I expect to find an alive plant.
The pH of the well-water in this area is 8 and the plant seems to do well with it. During the last rather dry summer I watered the plant about once a week and the soil became very dry between waterings.