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Hardiness:
Cold hardiness varies greatly with the bulb species,
the exposure temperature and its duration, and
the precise conditions in which the bulbs are
either packed or planted. In the latter situation,
the depth of planting, moisture content of the
soil, and the presence of a mulch affect the survival
of the bulb. In addition, the species and/or cultivar
can be a factor. Thus, hardiness is very complex.
Traditionally, bulbs have been classified as "Hardy",
"Semi-Hardy", or "Tender".
In addition, the usage has been largely confined
to bulbs planted outdoors. In reviewing the literature
on this subject, De Hertogh and Le Nard (Chapter
6, The Physiology of Flower Bulbs, 1993, Elsevier
Science Publishers, Amsterdam) have proposed the
following hardiness classification for flower
bulbs. Also, consult Sakai references.
Tender I: Injured below 68°F
(20°C)
Tender II: Injured below 50°F (10°C)
Tender III: Injured below 25°F (2°C)
Semi-Hardy: Injured below 28°F (-2°C)
Hardy I: Injured below 23°F (-5°C)
Hardy II: Injured below 14°F (-10°C)
Hardy III: Injured below 5°F (-5°C).
It was proposed that these classifications will
be more functional because they define upper and
lower temperature hardiness limits and these are
directly related to optimal growth and development
responses.
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