This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This is the best of the hardy Yuccas. It grows over 6 ft. high, and has dense rosettes of evergreen grey-green sword-like leaves up to 3 ft. in length, above which tower the thick branching spikes of white or greenish-white bell-shaped flowers resembling inverted Tulips. One of the best forms is recurvi-folia (fig. 449), but there is also a narrow-leaved form called angustifolia. Y. filamentosa is similar in appearance, but is recognized by having the edges of the leaves frayed into white thread-like filaments. The flower spikes often attain a height of 8 ft. There are forms known as jlaccida, with softer recurving leaves, and one with blue-green narrow leaves called glaucescens. Yuccas flourish in rich loamy or good garden soil, and are increased by suckers and seeds.
Fig. 449. - Yucca recurvifolia.