Yucca smalliana Bright Edge Sun Perennials But these are the exception

But these are the exception to the rule in these normally stationary plants

The answer

where they can cascade

That being said

Extended dry spells in summer can decrease blooming as is typical in their native range of Texas and Mexico

Yucca smalliana Bright Edge Sun Perennials But these are the exceptionYucca smalliana 'Bright Edge' is a striking small selection of the deer resistant , drought tolerant American Southeast native soapwort. The narrow, dark green leaves are edged with a wide band of creamy gold, whose color holds well through all seasons. In spring, the 18" tall x 2' wide Yucca 'Bright Edge' is topped with 4' tall stalks of white, bell shaped flowers great for rock gardens or the front of your perennial border.