I think a few Hydrangeas (mostly the ones I mentioned) are actually very good plants for the right spot in Colorado. The famous blue species (H. macrophylla) really needs a humid, wet environment and acid soils to perform its best. That said, I've seen some stellar plantings of the cultivar 'Endless Summer' in older parts of Denver (with probably more acid soil due to leaching over time). I would generally recommend most of the many kinds of Viburnum you can find locally over Hydrangeas (except for the ones I mentioned). Viburnums are less sensitive to soil alkalinity and can take it a tad drier. If your garden is truly baking hot, and your soil very alkaline, I'd stick to natives (and learn to underwater--they generally hate being wet!). Hope this helps.