Those all want full sun and good drainage, if the part that doesn't get rain is under a building overhang none of them will like it if there is much shading. Otherwise the natural precipitation will probably be adequate for all of them, once established. Any that appear to be having a problem during a future dry spell can always be rescued with a good soak at that point. Mulching the planting(s) with gravel would probably be a good idea - you always want to mulch ornamental plantings with something, and the kind of planting you are talking about here is one that would often be mulched with stone rather than organic material.

The most fussy about drainage is probably the lavender, in this region it seems a location cannot be too arid and austere for it.

I just got purple echinacea plants, too. They were on sale for $1.25!!!

Thanks for the response! It doesn't seem like the overhangs interfere too much with sunlight, especially in the dry bed.

It sounds like the lavender might need to go in either the dry bed, or the back of the other bed. Gotta figure out how the heights will work.

Goodness knows I have plenty of decent looking gravel around here!

The cone flowers will want to be watered and if they are one of the new cultivars with abnormal flower shapes (perhaps this applies to those with different than normal colors also) they will need to be kept divided and maybe fertilized as well. As is often the case with plant breeding the built up, fancy types do not have the vigor and stamina of the original version(s).

The previous owners of our house planted lavender in an east-facing border along our lawn, cornered between a fence and a tea rose. The lawn gets watered once a week in the summer, but the previous owners probably watered at least twice a week. Despite being in less-than-ideal conditions, it does just fine. Of course, we're a little drier (and perhaps sunnier) here in Western Oregon, but we still average 40" of rain per year. While most of the cultivated lavenders do prefer full sun and little summer water, you can often get away with less-than-ideal conditions in the garden.

Disease tolerance varies with cultivar.

I'm no lavender expert, but I imagine that most of the cultivars sold in the trade are on the disease-resistant side.

This post was edited by OregonGrape on Mon, Aug 26, 13 at 15:20

Sometimes you see tags on certain cultivars displayed at outlets here mentioning them being disease-resistant, specifically because that is not the dominant situation. As with other groups most kinds sold here are the same ones being grown elsewhere in the English-speaking world - and even beyond.

Bummer about the echinacea needing to be watered. I put it in the driest parts, because that's where it looked best. Ah well. I guess I'll see how it goes with a little watering, and if they don't like it, I'll replace them with more lavender next year.

I have the lavender and sedums in the driest parts, as well. Hope something thrives there!