Hardy Species Survey
Explanation & Caveats
by Joe Bruso
|Feedback Questions for All Massachusetts Chapter
If you have grown this species outdoors: Species
1. Do you still have it? __Yes __No
2. How long have you had it? __years __1-5 __6 or
3. Has it flowered for you? __Yes __No
4. Is it a reliable performer for you? __Yes __No
5. Comments on cultivars of species you grow?
How we obtained Survey data
Survey data were obtained via three
- Hardiness Survey Questionnaire sent to Massachusetts
Chapter members. We particularly targeted members known to the
Species Study Group to be growing a number of species.
- "Species in our Midst" questionnaire. Each month, the
Species Study Group publishes in the Massachusetts Chapter
Newsletter a "species profile" titled
"Species in our Midst". At the end of each profile is a brief
questionnaire, which we ask members who have grown this species to
fill out and return.
- Species Group consensus experience. This was a consensus
rating by Species Group members of species we have had personal
experience with, as well as knowledge of others'
Hardiness Survey Questionnaire
We created a database with the names of all
non-vireya Rhododendron species. The source of all names was The
Genus Rhododendron: Its classification & synonymy by David
Chamberlain et. al.
Hardiness ratings were added for each species
whenever possible (for some species we found no source for
ratings). The starting point for these ratings was Greer's
Guidebook to Available Rhododendrons by Harold Greer. These
ratings appear in the leftmost Hardiness column, under "Greer".
We amended or confirmed Greer's ratings
using information from the following additional sources:
- The Encyclopedia of Rhododendron Species by Peter &
- Azaleas by Fred C. Galle.
- Species Group members' experience.
These ratings appear in the right-hand Hardiness
column under "Other".
From this compilation of data we extracted and
produced a comprehensive list, which we call our "Master List", of
species that could reasonably be expected to survive, if not thrive
in New England. That is, they have a hardiness rating of
-5° F or lower. Using this
list, we created the Hardiness Survey Questionnaire.
Definitions for selected fields on the Survey Responses detail
Name – We've consolidated our
data at the species-level. Note that there can be considerable
variation in hardiness among the subspecies, varieties etc. within
a species. For example, minus ssp. chapmanii is borderline hardy in
New England whereas minus ssp. minus, Carolinianum group is very
hardy in New England. There can also be great variation in
hardiness among plants within the same species/subspecies, which
have a different geographic origin, or are from different
elevations. Plants from higher latitudes and/or elevations are
often hardier than their lower latitude/elevation relatives. For
example, viscosum from Maine is much hardier than viscosum from
Type – indicates the broad group in
which each species belongs. We chose to use less technical
terminology than classification by sub-genus, section and
- Azalea, Deciduous
- Azalea, Evergreen
- Elepidote – without scales
- Lepidote – with scales
- Other – other than the above (a few odd-balls)
Hardiness: Greer/Other - Described in
Group Rating - A consensus rating of the
Species Study Group. Values:
Recommend. These are the "Good Doers" which should do very
well in many, if not all New England zones. They can be expected to
look healthy and to bloom.
B = Conditionally
Recommend. These are species for which the data are not as
clear-cut. They may do very well for some growers, but not for
others. Some may survive, but may not thrive without special
treatment of some sort (for example, winter protection, or constant
C = Not Enough
Data. Some of these species may some day be determined to
be "Good Doers". We do not currently have enough data to make a
conclusion about these. This rating was given to most species for
which we had three or fewer observations, or for which we felt
additional experience was needed.
D = Not
Recommended. These species have proven themselves to be
"reliably unreliable" in New England. Some have never been
successfully grown. Some may survive, but will not thrive unless
given special conditions and/or care. Only experienced growers
looking for a challenge should expend effort on these.
Still Own? – Is the plant still
alive in the garden.
Years Owned – Mostly as-of 1997
when the Hardiness Survey questionnaire was distributed.
Flowered? – Has the plant ever
Healthy? – Does the plant look good
and grow well.
Zone – New
England zones for which we have data range from 4A to 7A.
- From the data we obtained and our best judgement, species
listed on the "A" list can be expected to do better in New England
than species on the "B" list. Species in the "B" list can be
expected to do better than those on the "D" list. However, "your
results may vary". Growers’ personal habits, skills,
microclimates, the source of the plant, and other factors may cause
one to succeed where others have failed, and vice versa.
- Hardiness ratings for some species may be understated for
one or more of the following reasons:
- Hardiness may vary among subspecies, varieties etc. of a
- Plants originating at higher altitudes or more northerly
latitudes can be hardier.
- Some species’ ratings are based on the lowest
temperatures recorded in relatively mild climates. They have not
yet been adequately tested in New England's coldest
- Winter hardiness is not the only factor in success. Some
species survive cold New England winters only to die in the heat
and dryness of summer.