Here Verbena bonensiaris will often overwinter with a good snow cover and a little slope for drainage, also many of the deciduous agapanthus survive quite well and eucomis (pineapple lilies) have been much hardier than I expected. Oh, also some of the calla lilies might be worth trying.

While the subject of your Ericas is back, I've made an interesting observation

Kramer's Rote - serious damage

Ghost Hills or similar pink w/green foliage: moderate damage

Katia: no damage (it's white on green)

I see parallels to other Ericaceae where white or lighter flowered species or cultivars of certain species tend to be among the hardiest. Although now that I read Katia is a sport of Silberschmelze*, one wonders if that is explicative as well. (maybe the sport has a different or mixed level of ploidy)

* exactly the sort of information I'll miss when Heaths and Heathers closes...

All the same based on my experiences (and Henry's too, apparently) I have no idea how E. darleyensis cultivars got a zone 6 rating. They really should be zone 7.

That's a fun question ! I wonder if rosemary is of interest to you ? I've been successful at overwintering mine indoors this year (so far) but there'd be no hope outdoors - here zone pushing would be to zone 5 at best. .

I'll second verbena bonariensis. If it doesn't return, you'll still get lots of seedlings. Either way, it's long blooming and attracts pollinators. Have you grown cannas before? Those will sometimes survive for me (zone 6b) as well as elephant ears. I've had a patch of Salvia 'Black and Blue' for many years that keeps coming back. We often don't have snow cover when it drops below zero which is not good. This year we did, so I'm hopeful that I'll have some "annual" salvias return that I covered with leaves and a plastic bag.

I have tried cannas and they didn’t return. Might try them again as before I didn’t know the cultivar.

Sounds like you’ve got a great microclimate going with that snow cover. You could try pushing things like Rosemary (hardier varieties), Fig with protection, or even Lavender, snow insulation can really help them survive colder zones.

Try Musa basjoo (Japanese Fiber Banana)! I am in Zone 7a/b NJ but read they can take zone 5. The bananas will die down to the corms after a heavy freeze. Growers cover their beds with staw and some tqrp. Corms are HUGE once established, plants grow to at least 12 feet in a season! Only thing is the large leaves should be protected from high winds.

I have musa basjoo but they end up looking sad and small every year.

Tecnically, I am only .5 to 1 zone milder than you, telling you they grow HUGE here. Not sure what the difference is. Corms are literally at least ONE FOOT in diameter, and 12 plus tall trees every year over multiple years. Did you cover yours with straw and tarp? I will post a pic this year. i just bought another clump for my own yard.

I cover mine with tons of leaves every year. I think the reason is because we don’t get extremely warm in the summer and their growing is slowed

Good point, hot as Hades here in the Summer, it is Winter here until it is Summer and then Summer never wants to end!