We originally got Agave americana 'Opal' from Mark Shealy in Virginia who claimed it to be winter hardy near Roanoke. Our plants did survive below 10 degrees F, but damage was too severe to claim it reliable in Zone 7b. Agave americana 'Opal' is one of the many yellow-edged Agave americana forms sold under the group name "Marginata". This particular clone makes a large, upright clump of sharp-spined, blue-grey foliage with an attractive creamy yellow edge. Our oldest clumps are 3' tall x 4' wide, but in warmer climates they will grow larger, eventually producing a 20' tall flagpole-like flower stalk...a great hummingbird magnet. In colder climates, Agave americana 'Opal' is great for large summer containers.