Some of the readers may know Fritz Hochstätter, as the author of several books about Pediocactus and Sclerocactus, and now also Yucca books:

YUCCA (vol. I)  In the SOUTHWEST and MIDWEST of the USA and CANADA
                                    The dehiscent fruited species. Revised ed. 2000. 256 pages, Hard bound, glossy paper,
                                    150 color photos, 10 distribution maps, drawings (seeds, inflorescence, root systems),
                                    text in English, with german summary.
                                    PRICE: DM 165,- -- plus pp.
                                    Published in May 2000.
More information on the authors website.

YUCCA (vol. II)  In the SOUTHWEST and MIDWEST of the USA and CANADA
                                    Indehiscent-fruited species. Revised ed. 2000. 340 pages, Hard bound, glossy paper,
                                    289 color photos, distribution maps, drawings (seeds, inflorescence, root systems),
                                    text in English, with german summary.
                                    Published in 2002.
More information on the authors website.

YUCCA (vol. III) Mexico
                                    Indehiscent-fruited  and Dehiscent fruited species. published 2004, 304 pages, Hard bound, glossy paper,
                                    252 color photos, 7 maps, 8 drawings and 18 SEM's.
                                    text in English, with german summary.
                                    Published in 2002.
More information on the authors website.

The books are the best updated and revised books about the Genus Yucca since McKelvey in 1937 and 1947!

Fig 1.
Yucca sp. (Filamentosa/flaccida complex)
Photo by Fritz Hochstätter Copyright © 1999-2005.

Fritz has one of the largest collection of hardy Yuccas in the world. In his garden he has the following species and forms in cultivation:

Yucca arkansana
Yucca arkansana ssp. louisianensis
Yucca arkansana ssp. freemanii
Yucca angustissima
Yucca angustissima ssp. avia
Yucca angustissima ssp. kanabensis
Yucca angustissima ssp. toftiae
Yucca baccata
Yucca baccata ssp. vespertina
Yucca baileyi
Yucca baileyi fa. bella (H. Künzler, New Mexico)
Yucca baileyi ssp. intermedia
Yucca 'Chilensis'
Yucca 'Cochabamba'
Yucca 'Danica'
Yucca elata
Yucca elata ssp. utahensis
Yucca faxoniana (protected against winter moisture)
Yucca 'Flexilis'
Yucca filamentosa several forms and clones.
Yucca flaccida several forms and clones.
Yucca gloriosa
Yucca gloriosa forma robusta
Yucca gloriosa forma variegata
Yucca glauca
Yucca glauca ssp. albertana
Yucca glauca ssp. stricta
Yucca harrimaniae
Yucca harrimaniae ssp. gilbertiana
Yucca harrimaniae ssp. neomexicana
Yucca harrimaniae ssp. sterilis
Yucca 'Karlsruhensis'
Yucca nana
Yucca recurvifolia several forms and clones.
Yucca pallida
Yucca rupicola (protected against winter moisture)
Yucca rostrata (protected against winter moisture)
Yucca thompsoniana (protected against winter moisture)
Yucca 'Vittorio Emanuele II
Yucca whipplei (protected against winter moisture)

All the above species are hardy in the Mannheim area!

Fig 2.
Yucca elata (this plant is one of the "parents" of Yucca 'Filata'!)
Photo by Fritz Hochstätter Copyright © 1999-2005.

Yucca filamentosa x elata, (Yucca 'Filata') made by Fritz Hochstaetter in 1999, fh 1180.88.
Yucca flaccida x pallida, Maybe Fritz Hochstaetter 2007?
Yucca thompsoniana x recurvifolia, (Yucca 'Thompsonifolia') made by Fritz Hochstaetter in 2002.

More information about hybrids.

Climate information for Mannheim:
Yearly average of 600-700 mm precipitation per year or a little bit more.
Average of ca. min.- 12C to - 15C as the yearly minimum temperature (but it's rare and only for a short time)

Fritz Hochstätter, has the largest varieties of Yucca seeds for sale on his seed list, you can see the seed list or read more about his business at:

Navajo Country, hosted by the Cactus Plant Mall: