Yucca Rostrata
Hesperaloe Parviflora
Yucca Filamentosa

I think there are several othe species that will survive MD conditions. Y.rostrata is nice because it is trunking and looks very tropical. H.parviflora is a great clumping aloe that has long lasting beautiful coral colored flowers. The Y.filamentosa is reliable and flowers are white and bell shaped.

-David

Yucca Color Guard is very pretty varigated leaves.

Description....
Yucca 'Color Guard' is a wonderful middle variegated plant with creamy yellow centers and blue-green edges. It adds an excellent foliage accent to the hot, sunny garden and looks great with dark leaved plants such as Sedum 'Xenox', Geranium 'Midnight Reiter', or Geranium 'Elizabeth Ann'.

Height: 24 - 36" Spacing: 18 - 24"
Light: Full sun to part sun Soil: Average to rich, well-draining
Bloom Time: Summer Zones: 4 - 10

I have Yucca rostrata and Yucca thompsoniana along with 2 Agave ovatifolias outside right now...despite near record lows, ridiculous snow and ice storms, they all look great!

What impresses me most about the Agave is that it is exposed in a pot, so its root-zone is more compromised than if it was in the ground. I don't want to get too excited just yet, let's wait until spring and see if it really did survive.

As for the Yuccas - I think that hot, wet and humid summers might be more of a threat than a Zone 7 winter. Make sure the soil drains exceptionally well.

x

Yucca glauca, Yucca filmantosa, yucca rostrata var linearifolia (possibly). It is new to cultivation so hardiness estimates vary all over the place. some say 9b and some Z6. God it is a beauty, but so is Y. Rrostrata 'sapphire sky'. They do like it drier with good drainage. There are ones that are indigenous to non deesert areas. Yucca aloifolia is good to 7a and a humid lover. Yucca gloriosa is good to Z6a and is tolerant to moisture and humidity, Yucca recurvifolia (7a) likes humidity. Yucca flacida Z4b will grow in humid areas.

I have a very healthy set of Yucca filmantosa in my yard. The previous homeowner was not a green thumb. She lived here 5 years and these puppies are huge without any help from myself! If you live in northeast MD, I would be willing to let you dig up as many as you want from my yard!