Sounds like a plan! Love your garden and pond. Very pretty. :) When you see our examples, often the berm on the lower side of the rain garden is on the edge of the garden. Yours, since you are adding onto an existing garden might be in the middle of the bed. That is ok. Love that you are incorporating this into your existing landscape so seamlessly!

I've grown it in an area that could occassionally flood. I felt the combination that would do it in, was wet during dormancy. The best culture does seem to be a bit drier though. I have cernuum I've grown from seed in a several areas around my house now. It's easy to grow, it took me four years to flower though from August sown seed. Cernuum is the most moisture tolerant allium I've ever grown, but still...just FYI :)That's the best color I have from the seed grown, the typical is a paler pink. May I suggest some plants? (I still don't know what zone rating the OP has) I do natives quite a lot, I grew hibiscus coccineus (in fact most hibiscus) and asclepias incarnata, LA iris cultivars on the edges of my pond at a past house. They all did exceptionally well (compared to any plantings I've done of these before or since), and I think would thrive in the conditions, I also don't know how much (and when) your rainfall occurs. Other candidates would be lobelia cardinalis and siphylitica. I also had Michigan lily (lilium michiganese) growing not quite in the water, but only a couple feet from it...they appreciate wet feet.Just some photographic suggestions...all photos are my own from my plantings. All these seem tolerant enough to me to be able to handle some dryness along with inundation, though again with different rain patterns than mine perhaps, who knows?

It sounds like a good idea to attach a pipe to your downspout and bring the stormwater into a rain garden in your front yard. If your yard is fairly flat, you could dig a trench for the pipe at a slight downward angle, then add a pop up to bring the water up to the rain garden. I like the idea of putting the garden in the front corner! It looks like your yard slopes towards that corner as well. If your neighborhood has a neater front yard look to it, you could put in short massed plants like canada anemone, fox sedge, wild geranium and blue flag iris.

And a month later, I'm back with an update and questions. :) Finally located most of my needed plants a couple of weeks ago, and then it took almost 2 weeks to do all the digging. Here is my husband working on the digging, with some help from my cat, lol: Here it is leveled and ready for planting: The inlet freshly installed, but not yet buried: And here it is mostly planted, with some empty spaces left for the plants I have yet to acquire (and the edging for that top portion): Which brings me to my questions. :) 1. If you look closely, you can see at the bottom of the most recent photo the edge of the concrete walk. The berm pretty much starts right at the walk, which I did not plan but it seemed like it needed to happen that way because that edge of the garden is about 3 inches lower than the top edge. (Top of the photo.) I felt like it needed that extra reinforcement, instead of leaving the 6" flat at the edge. You can see the blue eyed grass I have planted there, BUT...I think I need more? It seems like if it rained really hard right now the edge of the berm would start to erode away. 2. Take a look at this photo, I tried to take it so you could closely see the inside of the berm: (I just noticed the photobombing golfball in there, lol...I don't even know, lol) So the depth of the berm is about 8-9". I'm worried that the whole thing is going to erode *down into the bottom* even with the mulch on it. So my question is this: Can I mulch this with leaves instead of something more chunky, like woodchips? I'm thinking the leaves, if I water them down after placing them, will hold things in place better. Should I plant more in the sides of the berm? Thoughts? Thank for any and all ideas. :)