We detail each bulb's ornamental features, collection
(if applicable), height, month(s) of bloom (in our USDA zone 5b locale,
except as noted), Royal Horticultural Society awards received (AGM =
Award of Garden Merit; AM = Award of Merit; FCC = First Class
Certificate), and cultural preferences. We base our descriptions on
personal experience, reliable references, and educated guesswork. To
estimate bloom time in your
area, multiply the difference between our USDA zone number and yours by
1 to 2 weeks. Unless otherwise indicated, listed bulbs favor full
sun (while in leaf) and well-drained, reasonably fertile soil. Their
other cultural preferences -- and their likelihood of success in your
region -- vary widely, however, depending largely on their native
climate, which we categorize thus:
- Montane: Cold, snowy winters; cool, moist springs;
dryish to moist summers. U.S. geographical range: western mountains.
- Maritime: Cool to cold, moist winters; cloudy springs;
mild, moist summers. Range: coastal Northeast; immediate coastal
- Modified continental: Cold to cool, moist winters;
moist summers. Range: eastern Midwest; interior Northeast;
Mid-Atlantic; upper South.
- Continental: Cold to cool, dryish winters; hot,
droughty summers. Range: western Midwest; Plains.
- Steppe (Cold Mediterranean): Cold, relatively moist
winters; dry, hot summers. Range: interior Northwest to Great Basin.
- Mediterranean: Mild, relatively moist winters; mild to
hot, dry summers. Range: western California; interior coastal
- Subtropical: Mild, dry to moist winters; warm to hot,
damp summers. Range: lower South.
- Tropical: Warm to hot winters and summers. Range:
Of course, we oversimplify climate's infinite variety. Moreover,
you shouldn't dismiss a bulb merely because its native climate differs
from yours; it may, in fact, thrive (and if it doesn't flourish in the
open, it might do so in the shelter of a greenhouse, bulb frame, or
south-facing wall). But the above generalities should help you
determine the plants and cultural
methods best suited to your conditions. For example, most bulbs
from dry-summer climates require porous soil if grown in wet-summer
regions, just as bulbs from wet-summer climates often need supplemental
summer irrigation in dry-summer areas.
Additionally, we include (with some hesitation) a conservative
estimate of the USDA zone to which each bulb is cold-hardy .
Keep in mind, however, that a bulb's tolerances
vary widely with cultural conditions and climate. For example, many
steppe and Mediterranean bulbs considered tender in Great Britain and
other maritime regions are quite hardy in hot-summer areas of the U.S
(casting suspicion on the hardiness ratings of British references such
as the RHS Manual of Bulbs ). Moreover, some extremely
cold-hardy bulbs are intolerant of hot summers or mild winters. Unless
its native range is known,
a bulb's hardiness ratings -- particularly if it is rare in U.S.
gardens -- mean little (and they should always be viewed with at least
a trace of skepticism). As for us (and for most other plant fanatics,
many of whom consider hardiness ratings to be a contemptible canard),
we usually assume a plant to be at least a zone hardier than its
customary rating, until proven otherwise.