Thanks Rina. Yea semps do t root deep which is why I thought 3 to 4" would be more than good. I excavated deeper becuase the native soil is clay and crap for drainage. So wanted to get rid of it and place gravel. Yes there will be settling eventually but it's still better than native soil.

Hmm no perlite for the bed actually makes me happy.

I agree with Rina, no need for perlite. Mix some small grit in. I would cover the sod underneath with cardboard to ensure it dies before it grows through the soil you add.

Also, you don't need a rain cover for Semps. Freezing rain won't hurt them. I grow many species/varieties in zone 5 or 6, your plants willbe fine uncovered.

Meant to add that snow cover I winter is a good thing, as it insulates them..

Breton, I've lost potted semps that i had underneath my patio stairs from what I like to believe was water quickly freezing over. Usually with the wind the rain got under the stairs, wet the pots and the pot that was not burried in the ground had a dead semp. That night the temps dropped well below freezing and it was windy. Granted the semp was a 1 year old pup. The year before that, same setting, I lost a few. So you can see in a little worried. Although I've been improving the survival rate, I'm trying to do the best for the semps.

Now, I've seen many many homes around Toronto with loads of semps growing in poorly draining soil and they all look happy and healthy, so that gives me hope.

Yea the cover in top should not block the snow, only the rain if it's not windy will not fall on the bed.

Perhaps they did not get enough airflow under your patio stairs? What kind of soil were they in?

As you can see there is gravel and Ive dug out a bit to make space for the pots. The soil is the old mix, cac soil with pea gravel and small lava rock pieces. All of the new pots have cac soil + perlite + safeTsorb mix (very light).

Looks like you've gotten excellent advice, just chiming in. Though I have no snow or freezing I do have tons of winter rains. I grow a lot of semps, some n the native hard clay soil which doesn't seem to harm them. I do lose some from rot, up to 5 months of non-stop rain is the assumed culprit. I always pull a few of the nice ones out in late fall, in case I lose a lot from rot, I'll have mother stock to start over. I overwinter them on a tray with only a small portion of the roots and soil still on. Some go in a dry house, some under shelter where they are fairly dry but cold and darkish. Maybe you could do that with some of yours, until you work out exactly how to get them through your winter. Maybe a basement window or other indoor/outdoor space? thoughts anyone??