Hi Jane, If I understand the concept correctly, you intend to use a lot of native plants in the border that your are planning. If so, my experience in New Mexico may be adaptable to your situation. I've been experimenting with native plants for quite a few years. I have planted native (western US dryland species including New Mexico endemics) in pure native soil with great success. I've also lost numerous plants to rot, or quick soft growth that does not withstand weather changes, etc., in amended soil. Penstemons particularly suffer under such cultural conditions, resulting in their reputation for being short-lived. Therefore, I urge caution in amending the soil at all. For those plants not adapted to the climate and soil, add a small amount of organic material such as non-manure-based compost to the planting hole and immediate area Sounds like a fun project! Barbara L. Weintraub Santa Fe, NM 87508-8769 blweintraub1@earthlink.net