Hugo Morvan wrote:Welcome to Permies Rose!
Nice wall! The earth looks really sandy. water will drain easily then. Not easy to grow things there. Great some weeds are already there building back up this disturbed soil. Their seeds have been waiting for that moment. Usually the green roofs people have turn brown/yellow in summer. The layer is not deep enough so the grass can't get any water from deeper layers. Those weeds look pretty resilient. They might have a deep taproot and be happy enough with not a lot of nutrients. But they keep the soil in place! Very important on top of the root cellar.
The sides are still exposed to the sun and erosion. Maybe pebble it up? And look for some other low maintenance plant on your terrain that could grow in between those pebbles. You need the roots to keep it all in place.
If it were me i'd let the weeds do their thing and plant something down the sides that can root deep and cover the top. Wisteria springs to mind. It will fix nitrogen at its roots. Maybe chuck in some left over wood debris into the weeds so the wisteria got something to grow above the weeds and shade them out and take over slowly.

I like the idea of picking something that can grow up from the sides over the top. Wisteria isn't going to work though because I just read that as few as two seeds can kill a child! I've got seven little children that routinely forage my weeds so edible is a must.

Arctic roses grow very well here but they're a little big. Maybe thyme? Mint, maybe? I'm not very good at this, hence why I'm here.

Jay Angler wrote:What about naturally low-growing shrubs like wild blueberry?

That's an interesting idea. They do grow wild around here. Do you know if they would be able to resist the weeds? 🤔

I forgot to mention that the slope is squarely southfacing. We're in northern BC, zone 5b. I'll try to edit the original post.

We built a root cellar on our property over the last few years. We filled it in last spring and now have a year of weed growth on top. We've built a terrace above and some retaining walls at the bottom. Originally, many years before we bought this place, our land was all a slope but somebody excavated a large plateau midway up the slope and placed a mobilehome on the property (talk about raping the land!).  We built our cellar into the back remaining hillside. What I'm struggling to work out is what to do with the hill. The slope is quite steep but seems stable. We transplanted some wild raspberries and have plant grapes along side the ugly trellis. What else could we grow here besides giant clover, burdock, dock, thistles and dandelions? We need things that can hold their own and stablize the soil.

For reference, we're in northern BC, zone 5b.