I'd add the pine fines as long as the only water the bed gets is what comes from the sky. Also provide lots of air circulation. I found that's what REALLY got my "dryland" beds in Kansas--not enough air circulation with that relatively (compared to Nevada) wet air. Also, add a gravel or rock mulch around the crowns before winter. That helps a lot of things survive my Nevada clay soil without improving the drainage one bit.

The only way I have found to take clay to sharp drainage is to remove most of it and do a lot of labor mixing in sand and gravel with a bit of organic matter and some of the clay. I then make that soil into mounds so they can drain quickly. The leftover mounds of clay also have decent drainage although not sharp and some of the clay hearty plants do fine there.

If you don't have time to do the labor select really drought tolerant plants that are clay adapted. A lot of prairie grasses will get the soil moving in the right direction in terms of water soaking in & adding organic matter. Prickly pear (maybe the spineless kind is always a safe bet. Some Yucca or agaves and then some wildflowers as you were describing.

Let me reinforce what Kate Rose said about mixing sand, gravel and OM into the clay............REMOVE most of the clay and mix back in SOME of the clay.........very little "some." Clay particles are microscopic whereas sand and gravel particles are so large they are visible. To separate all those clay particles so they don't turn into adobe requires in incredible amount of coarser material. If you don't add enough, you've just created "organic concrete," something actually worse than the clay......if that's possible.

"Let me reinforce what Kate Rose said about mixing sand, gravel and OM into the clay............REMOVE most of the clay and mix back in SOME of the clay.........very little "some." Clay particles are microscopic whereas sand and gravel particles are so large they are visible. To separate all those clay particles so they don't turn into adobe requires in incredible amount of coarser material. If you don't add enough, you've just created "organic concrete," something actually worse than the clay......if that's possible."

I can vouch for this. Some people I was working for at IU thought they could make the Indiana clay well-draining by mixing in sand--instead it was worse. The plants in it did fine, but then again they'd been doing fine in the clay outside, too...

Also worth mentioning is that sand, while usually thought to be well-draining, actually holds water very well. This is why, for instance, water-loving plants like cottonwood will grow in pure sand at White Sands, but can't survive anywhere in the surrounding flats that get just as much rain. Sand doesn't hold nearly as much water as most other soils, but it's got a tight grip on what water it does hold.

Personally, I wouldn't bother with sand. For lightening clay soils, relatively porous gravel (or artificial equivalents like Turface) is good, and organic matter is good. Sand is break-even at best, same with smooth, impermeable gravel.

Patrick Alexander

i have read that crushed shale is much better than sand at loosening up clay soil. this is what i intend to use on mine. and i know many who have had great success doing it with compost and vermiculture. this i will use in beds w/more delicate plants.
good luck!