Did you ever think to protect your T. Fortuneis? Perhaps that would get them to a size where they could deal with the cold like the one that is growing well in Sterling, VA. Hardiness varies in individuals and in seed lots so you may have a hardy strain of T. Wagnerianus as I have found them to be only as hardy as T. Fortunei. As I recall your palms seem very small for their age and their location seems less than idea in their setting.

my potted 5 gallon waggie spent it's winter on a closed sun porch with some takil seedlings. temps never went below 25f and all had spear pull.waggie is recovering with new spear emerging but takil seedlings(quart size) are dead.2 one gallon fortunis had spear pull, but 5 gallon size did fine. go figure!

Having those palms in pots in an exposed porch where their root zone can freeze is much harder on them than being in the ground with lower temperatures. Seedlings of any cold hardy palm are vulnerable to cold temperatures.

I went out and took some photos of the "runt" waggie last night:

Closeup of the emerging spear:

My other waggies are much larger, have been in the ground for about 5 years, and are quite healthy. I suppose I could try to "push" them but this species is both smaller and generally slower growing than T. fortunei. I have no idea how big they "should" be at 5-6 years old from seed (they have certainly been set back by some hard winters), but several growers who are far more experienced than I am with this species have told me that the growth rate of my palms is about to be expected. As long as my plants are healthy and growing, I'm happy with them and don't need to see instant results. The challenge, and the fun, are in the growing.

virginian,I think your right. the cold temps were hard on these potted palms, plus on a sunny day this sunroom would heat up to 80 degress and rthen plummet at night.All are growing their spears back except the 1 quart "takils" that croaked.I was trying to harden them up and not expose them to very warm and dry house temps.

raising night greenhouse/sunroom temperature at no cost with thermal mass heat exchange. Try placing 2 water filled large black capped olive containers in the room. This raises greenhouses temperature at night substantially.