Re: Some Fall pics of zone 4 Yucca
very nice pictures of healthy Yuccas. Are you sure no. 1 is Y. gloriosa? My first impression was Y. filamentosa/flaccida but maybe the picture isn't that clear. It's impressing to see in which regions Yuccas can grow. Zone 4 sounds pretty cold. What was your lowest temperature of the last few years?
I too grow some of the Yuccas in my garden but in zone 7a (Germany, near Stuttgart). Is the Yucca 'Kaktusgarten' x elata a Y. filamentosa 'Kartausgarten' x elata 'White Sands' made by Jürgen Bredow, Germany? I also grow Yucca flaccida Bright Edge x thompsoniana and a "Big Mama" from Tim and a lot more.
You have been much more successful with creating hybrids than me, I only got one seed pot of Yucca (filamentosa x glauca) x karlsruhensis. If you like we can swap seeds. I like hybrids with trunk forming Yuccas and maybe the hybrids with Y gloriosa will form a trunk.