I have acquired the habit of making multiple vertical slits with a utility knife in all potted material that I put in the ground. Something in a 3 gallon container that was very root-bound would get 6-8 vertical cuts to the full depth of the blade. This operation helps guard against circling (girdling) roots & the possibility of water/nutrient flow being cut off later. The injury to roots also generates chemical messages that stimulate quicker root (re)generation. Though some container gardeners can come close to growing plants temporarily at nearly peak potential genetic vigor (when everything is just right), it is a good bet that o/a vigor and and a jump on getting the plant established in soil would be enhanced by planting out now. I think the main concern would be getting the plant enough water during its period of establishment. Al

I was thinking about planting this too but decided not to after reading responses from Dave's Garden website where I get a lot of research info. I live in Minnesota. What I read was that this shrub really needs a good 6 hours of sunlight daily. I don't have that much of it where I wanted to plant it. If you lives in the Carolina's or there about it would probably grow better. One guy said that he planted it in an old gravel road and it tripled in size in one year, but then he was in North Carolina. I don't think that it thrives in our winters.

Slightly alkaline unamended blackland clay. They're in an area enclosed by sidewalk and a semi-circle drive competing with a large Chinese pistache and the 6ft+ boxwood hedge they're growing to replace. Rabbits don't seem to eat it, but like to hang out under it when browsing most of the other ground-covers we've been trying in that space. It eventually becomes very broad, but is slow growing; so for now we've filled it's mature footprint with temporary salvias, lantanas, and a few other things. Those plants have needed more water and attention than the sumacs. Think there's a very good chance it would do fine in your spot.

Just so you know, getting any plant established will require watering on a regular basis the first season, so plan on doing that and get the length of hose needed. One suggestion would be to lay hose under the mulch with a sprinkler set at the top of the slope and leave it there so that all you have to do is hook it up to the water and turn it on whenever it's dry. The fewer times you have to walk on the slope, the better, so you might want to ask your up hill neighbor if you can use his yard for access the first season since it's also to his benefit to have the slope stable in the long run. Or use the stake and board method below to build a temporary set of steps. Or a more permanent set along with a path across the midslope for easier access when needed. I have a steep sandy hill from an old river channel that was disrupted by construction in a few areas, and here is what we did. We began by doing things to stabilize the slope on a short-term basis. First DH created a bunch of 2' wood stakes and got long boards (just pine sawmill cutoffs) which he staked in place across the slope, slightly below the soil line, but mostly above. I followed with a rough mulch that knitted together well and didn't slide down the slope. Look for gorilla hair mulch or chipped arborists' trimmings, both of which work well. I did a lot of the work from the top of the slope since gravity helped me out. face on - Over to the left by the concrete wall ( which was poured as part of the building's foundation) you can see some of the boards. Looking across the slope you can see some of the stakes sticking up. There are boards under the mulch. Once you have done that, then you can start working on your wall and planting the upper part of the slope. I agree that a modular concrete block wall would be the way to go, though I would also check into a poured concrete wall to see if that may be cheaper and/or more stable in the long run. Read up on how it needs to be built to be safe - tying back into the slope and a proper foundation. Plan on getting all the materials and doing the work in chunks so that you don't have exposed soil for long periods of time. I would be more likely to do a two or three foot wall to decrease the slope's steepness and then use plants to stabilize the remainder of the slope. Multiple walls that together equal more than a certain height need engineering to be stable. My slope pictured above is in shade most of the day, so the plants I used there won't help you much. In another sunnier spot I used a combination of old-fashioned orange daylilies (Hemerocallis fulva) which spread (unlike many of the modern daylily cultivars) along with Centaurea dealbata, a perennial magenta-flowered cornflower. Both spread vigorously and are in the range of 1 1/2' -2' tall out of bloom, and I usually weed the slope once or twice annually (takes about 20 minutes for 60'x15') and renew the mulch in very early spring every few years before the plants have sprouted to keep the weeds from getting a foothold. Here is a photo of the slope, freshly mulched early season before the plants came up. By now this is about 20 years old and only gets a few hours of attention per year on this west-facing slope. It is densely packed with plants and has flowers from late spring into summer, and I have added a few shrubs to the slope to provide interest when neither of the groundcovers are blooming. I got the Centaurea as a hand-me down plant from a neighbor and the daylilies were already on the property so I only had to divide and move them. You will most likely want to get started on your plantings in the spring, and if there is a plant source that will sell you flats or you know someone with either of these plants (or can find them somewhere like Craiglist), you can increase them over time with division.