We pulled out junipers and have sort of the same situation, at least in part, areas along the drive that are fairly steep and some areas along the street that are sloping. We added good-sized rocks (3 tons worth) to give a small amount of support and give it a natural look. They're just "scattered" (you don't really scatter 100# rocks!) and partly buried to give some structure to the area but don't form a wall. I did create pockets of 3-6 rocks in many places to serve as partial terraces. We're planting small shrubs, perennials, groundcovers, and grasses to keep the soil in place. Many of them are evergreen so will provide year-round interest. Some things are clumping but some are more spreading. I've tried to be careful to not select things that are too aggressive; for example, some of the thymes spread quite a bit but aren't going to swamp the area. My plan is that once things are more mature and I get a few more things planted, the roots will hold things in place well. This winter will tell a lot but from what I've seen in my walks around Vancouver and Portland, I'm on the right track.

If you want flower beds for annuals you might want to consider terracing or some sort of wall/support/structure. I've seen some nice examples that look very natural, if that's what you're after, and of course there are tons of examples of more formal looks. It's worth spending the time to look around at what others have done and do some research before you get started -- better to do any structural work up front than to have to struggle with soil erosion and problems later. If you're willing to do the research and put in some muscle, it's not that hard and not very expensive to do the work yourself, depending on what you want to do.

Good luck!

I found interesting info on how to plant a hillside at the website for laspilitas nursery (natives in California). They have plant lists but also how to articles and one was planting on a hillside. There is an article now at: http://www.laspilitas.com/garden/howto/slope.html but its not the same article I read 3 yrs ago.

I have a steep hill behind my house which was lawn, converted to drought tolerant perennials and shrubs. I wanted to remove the sod, rototil and add amendments but imagined the whole loose mess sliding down with the first good rains.

Their article was actually kind of entertainingly written - don't remove the grass, kill it and plant through the dead sod and cover it with a mulch but 'don't overestimate the ability of grass to recover and return' or something to that effect. Note tho that this was for planting natives/drought tolerant plants .

I round-up'd the hillside and once the grass died dug planting holes in the dead grass and amended each hole rather than the whole site. I made the only mistake of not believing the grass resurection part and ended up with grass reviving around all the plants during the rainy winter season so did make more work for myself by not covering with a mulch - I then had to remove the returning grass.

So I guess my main advice is not to disturb the existing area any more than necessary (if you don't currently have an erosion problem) and you shouldn't have erosion - my hill has been in for 3 summers now and I have never had a problem. My hill is not so steep as to need rock climbing ropes to work there (LasPiltas article) but steep enuf that balance has been a problem when working.

This is just an interesting option to retaining walls/terracing. Have fun and good luck