'Sedum tile' is not name of the plant, but a product . It could include one or few or many different plants. Your photo is not clear enough to ID, but I can see at least 3 different plants.

It doesn't matter too much, since many have similar requirements to grow: good drainage, good light.
Personally, I would use very little (if any) soil since it is planted in organic "container". I wouldn't use mulch either, rather some gravel top-dressing, or rocks. I don't use sand or vermiculite at all. Sand, and especially play sand, is very fine and not good at all for containers.
This tree stump is kind of container - but not same as much more enclosed pot.
I assume that it is recently cut tree since you say it is still alive? What kind of tree was it? Some will sucker after being cut like that.
I would fill up the stump with small grit and some perlite, and maybe 10-20% (of total volume) soil. The sedums should spread around, eventually filling up whole area and even hang around the edges. This is just what I would do - others may have different ideas and opinions.

I don't understand what you mean by: "Hoping to avoid again digging out soil that smells like hell's lavatories," ??? Are you digging over the septic bed or???

It's a maple, cut last year, before the winter. I'm surprised it seems to still be alive - it's sent up sap, and when I drilled 6" holes down it, the next morning they were full of water. It also has a new growth from a side now.

What is "small grit", and where would one buy it?

Re: smell, I made the mistake of using topsoil, which I also compacted. It rotted or gained lots o anaerobic respiration bacteria or whatever it does, and did the sulphur / rotten egg smell thing. To the extent it smelled worse than some actual sewage I've been near. I removed the sedum from it, which was surprisingly easy, I'll need to brush off the bad soil but I think it'll be fine. The sedum actually didn't show any health problems, the only reason I noticed the soil problem was that I removed some soil to run a low voltage DC cable (I made some fiber optic "plants" to go beside the sedum). But unlike removing the sedum, removing all the soil from the stump and then hosing out the remnants was very not fun.

Danny
Maple is notorious for sending up suckers, new shoots. It may need some 'intervention'.
There are many suggestions how to do it:
Epsom salt or rock salt (not table salt) - you need to drill holes into the wood, fill them with the salt. It has been recommended to seal top of holes with candle wax so it doesn't 'escape'.
Then cover the top with something non-porous - plastic, garbage bags have been suggested, but that may be unsightly. I would do it this way:
- put a square or round paving stone on top to cover all the holes
- pick up a round or square shallow container
- sit the container on top of the paver - fill the container with mixture of grit - about 50%, and you could use c&s soil and some perlite if you have too - and plant sedums in it. They should grow well.

(You don't plant directly over the stump - the salts are no good for the plants; if stump is exposed to lots of light and water, it will 'live' much longer.)

It will take apparently upwards of 6weeks to few mo for stump to die, eventually will start falling apart, you can help it by chopping dead chunks off. Or you could leaveit there to decompose naturally.

I don't have personal experience doing this.

You can also use chemicals, there are some sold as tree killers - you probably would do it similar way as for salts.

You can burn the stump - but fire is dangerous. Not sure if you can set it where you live.

You could chop it or have it done, there are stump grinder available to rent or hire ppl to do it. Could be pricey?

Rina

Just to add to above:
sedum will grow well in container just make sure it has drainage holes.
Here is trailing-kind of sedum that is planted in old concrete planter, it is trailing over the edges and looks like a large ball of plants - it sits on top of landscape rock, can't see the planter:

Rina

Figured out what grit is - really small stones between course sand and crushed stone, like 2-3mm - but I just called several landscaping and stone yard type places, no one had it :-/

Re: rina_Ontario - I don't want to get rid of the suckers. I like them, and they don't seem to be harming anything. And the stump being alive probably also increases the lifetime of the carved out "container". I'm just interested in suggestions for soil (or lack thereof) formulations for the sedum.

Danny
Sorry, forgot about that. I use chicken grit bought in farmers supply store, in 50lb bags. Inexpensive, it is crushed granite.

I obviously misunderstood - If you don't want to get rid of suckers, they will grow into trees. In the meantime, if it was mine, I would fill the stump with lots of grit+little soil. If I was concerned about drainage, I think I would drill few holes sideways (on the angle, from bottom of stump at soil line) - JMO!

The stump will eventually decompose without any help, but will take years. I think they are quite nice as a live containers and/or 'natural pedestals'...and will add organic component to the soil as it decomposes.

Rina

Ah, the nearest Agway is about 1.5h away. Hmmm... would aquarium gravel work for small grit stone? It's hella expensive, but for the small space it wouldn't be so bad. And based on my poor memory the size is about right.

Don't think the sucker will manage to grow into a tree about 8 inches from the curb; if it starts growing into the street I'm sure someone or the city will cut it (pic with more context below).

There are already plenty of drainage holes that work fine; the problem is the compacted topsoil was just sponging up the water. Even the soil right next to the holes was saturated, although the last rain was around a week ago.

(Photo upload seems to be broken at the moment - here is the photo I referred to.)

Ah it's not broken just insanely slow... here's a different picture; esp. if you click on it you can see the little sucker on the middle of the right hand side.