How to make poor soil?

I am planning on adding a small bed (which may expand into a border if it works well) of deer resistant, xeric plants, that prefer a very lean well drained soil.I'm thinking Lavenders and the like. My native soil is a glacial till mix of clay, silt and rock certainly lean, but hardly well drained and not at all easy to dig ( we have bent several small pick-axes trying). I have rather a lot of a very rich compost, loam, and sand mix that I use in my raised beds. What would I best add to that to lower the richness and increase the drainage and in about what proportions? Coarse sand and fine gravel? Or should I just mix something from scratch? I am gardening on the Sammamish Plateau just east of Seattle in US Zone 7, Sunset zone 4. Thanks for your thoughts.

Kyra

No expert here but richness usually refers to the amount of organic material. I once did a soil test on my native soil and it came 2.5% which is a little low. Some plants do prefer a medium or low (I guess it depends on what rich is to you) organic content because that's the conditions under which they evolved. I would do a drainage test first -

Dig a hole, fill it with water and see how long it takes to drain. If the soil is really dry do it twice, the first time will only wet the soil. If it takes many hours to drain it's slow draining. Less than an hour is good. I would add sand or coarse sand to improve drainage if necessary. I would think a little compost would be OK but you'd have to ask someone who is familiar with the species of plants you have selected.

Yes, Kyra. Coarse sand and gravel is a good choice to insure good drainage in a raised bed and to make a spare soil. After water flows through the soil you will build, it has a place to go - right? It won't just sit in the depression you make when you build the bed? It sounds like the stuff that rock/alpine gardens are made of. ;o) Good luck!

Al