I had mine on a slope for a couple of years and moved them because of lack of sunlight. They did well on the slope but I did have to use a landscape fabric stake to stake down a few that wanted to fall over the first year they bloomed. I used the stakes that look like a big staple.

I put iris on a slope with trees in my guy's yard because it's the only option. Planted last September and blooming now. Seem to be holding steady and not falling but they are only "old fashioned" type, I think.

Because the slope faces North, I think they are behind a full zone and I'm expecting less of a show per plant because of the shade.

I was very surprised to get blooms at all this year because I knew not to plant them deep but still might have been too deep. Now I know better. Plant 'em high!

I'd plant them there. It's hard to interplant with irises because if another plant grows over the rhizome it will rot.

I pull off dead foliage to keep the plants neat looking. If you planted some "s" shaped swoops of irises near the top of the slope and some low perennials just below them would it help?

Wow all great ideas and encouraging. I'm going to go ahead and do it! I like the idea of the landscape stakes to hold them if they tend to fall forward. Also like the 's' shape swoop idea rather than just randomly throwing them in. This area faces East so they'll get sun until about 2 because of the trees behind them on top of the berm. I hope that's enough sun. I think I'll limb up some trees...

I had experience with NO bloom on some gorgeous ones that bloomed last year - because of another plant growing over the rhizome - weeds. A weed I've been trying to get rid of for 20 years. I'll be digging up that whole bed and replanting it and next year I'll use a 'pre-emergent'.

Thanks everyone!

Westy

Would that weed happen to be black swallowwort? I've been fighting it for years and have a neighbor who has been fighting it for 40 years. If you find a pre emergent that works, please post it.

Here is a link that might be useful: Black swallowwort control

Not Black Swallowwort, happyday. I've had several people tell me it's 'Sheep's Sorrel' and someone told me it was 'pig' something. I'm going to take it to some experts at the master gardeners HQ here in a couple of weeks. The nurserymen just quibble amongst themselves when I've brought it in. It has a root system that is very shallow but it's like 'hair' because they are so fine and there are MILLIONS coming out of ONE plant. It will usually stay about 4 to eight inches tall but can smother anything because it grows so thick. The older they get (and taller) the easier they pull out of the ground but I'm done fighting it. I'm going to have to use something I don't like to use I think. I'm so angry they smothered my Iris!

Westy

Is this it? Sounds like Roundup will kill it.

Here is a link that might be useful: Sheeps Sorrel