I've been waiting to see if anyone chimes in here. Your description of the retaining wall is producing a charming picture in my head, but none of my heucheras has ever self seeded (I don't have a lot, but I have several Palace Purples). I suppose a combination of some deadheading and some weeding might be the reason. But I'm not a tidy gardener and my gardens are full of volunteers - just not heuchera seedlings. Hope someone can contribute here...
Jan

I have had a few of my Heucheras self seed, though they are not prolific. They self seed where the mulch is thin or on bare ground. The ones I have had self seed the most are Venus, Palace Purple, Dales Strain and Raspberry Ice.

The others I have would probably self seed if I didn't have my mulch so thick in my garden. I wintersow them every year and always have awesome germination so i know that if the conditions are right they would definitely seed like crazy.

Rhonda

I'm glad to hear that Palace Purple is a good germinator. I've received some seeds in trade and I'm looking forward to multiplying them in my gardens.

Martha

What do heuchera seeds look like? I've just collected what looks like dried flowers and can find nothing seed-like in there. Do only some varieties set seed?

I crush the pods between my fingers/hands-the seed look like black dust. A magnifying glass is helpful to see them.

I do not know of any heucheras that are sterile and I have quite a few varieties. All of them are good seed producers. Maybe someone else has experience with sterile varieties.

Rhonda.

I have had heuchera self seed, especially Purple Palace. I read somewhere that they don't come true from seed. Purple Palace and Dale's Strain are an exception in that they are similar to the parent. This has been my experience, some seedlings don't have the same coloring or leaf shape, although it is close. That's why nurseries propagate most heuchera from division or some method other than seed. Still, it is fun to see what pops up.

Beverly

I've had some "bird assisted volunteers" of heuchera "brownies" from a local park where I recognized them. Love them birds.
Lobo, rbrady does what I do and there are lots of seeds in that dust. Petite marbled burgundy gives a lot of seed for me, though when I grow from seed it takes a few years for the characteristics of the plant to fully develop.