In that picture it looks to me as if you hollowed out a broad area in which you created a smaller raised one. What keeps the inner mound from eroding? And is the crown really at the level of the overall slope? It looks lower.. My slope is much steeper than yours I think. Perhaps it is not even aesthetically suitable for a plant like a yucca which is both vertical but also has a broad "table" of leaves that really should be flat..

as if you hollowed out a broad area in which you created a smaller raised one.

==>>> yes.. the water retaining moat FOR A NEW TRANSPLANT... i dont care if and when it filled back in.. the tree would be free range by then ...

all plants will adjust to their location.. given time ... presuming you can get them established with enough water ...

yes its a very light slope.. but you have to water the darn transplants ... and you cant do that on a hill .... if you dont make a moat ...

yucca.. will probably never need water after the first year .. dont overthink this drought resistant plant ...

to be clear ... im telling you water is the most important variable with a transplant ... and its not easy to water on a hill ..... you seem to want to focus on other variables ... the first year.. all i care about.. is that they live.. they will adjust the next year..

but you can surely understand.. that i would not plant a tree or conifer.. on the angle of the slope .. so why would any other plant.. be planted that way ... unless you had some goal for something weird and unique ...

ken

We are growing a color guard yucca on a steep slope.

We planted it upright and it remains upright. As Ken noted, this plant likes it dry. I am sure that I would have created a level planting area for it, but not a big well. We live in a fairly rainy area, so drainage was most important. I have never watered it in three years.

BTW this is one of our favorite plants and is beautiful year round.

Mine is a colorguard too. Snapped it up on a clearance sale:)

But to the question of planting orientation on a slope. Certainly not all plants are planted upright. Blue rug junipers or anything intended to carpet the slope? There is a beautiful azalea-blanketed hillside nearby that sure looks as if you are looking at their tops, not into legs.. Or do legs not typically form on slope-planted specimens, rather with crowns spreading at a tilt to take advantage of the sun?

You say not to overthink the yucca, Ken, but it is a taprooted plant that is hard to move so this is a rare case where I am thinking.

I think those azaleas do grow uprightly, but their branches grow where they can have space and light, so they appear to drape down the slope, as you described the crowns spreading at a tilt. All plants grow toward the light really.

we werent talking about groundcover plants ... ken

Everything I have grows toward the sun, even if on a slope, and I have some steep ones. So steep I have to scoot around on my butt to weed.

And yes, I plant everything "level" initially so my little water retention system functions during establishment. Then they do what they want to do.

"Should I be thinking about this as I fill in the slope, or just assume
they will all take a harmonious and natural form with time?"

Don't worry about it- as I said plants are gonna do whatever they're gonna do and fighting Mother Nature to fit some aesthetic vision of perfection is a losing battle. Work with Mother Nature, not against her- plant so that initial new-plant watering needs are easily met then let the chips fall where they may.