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Most plants
available for your garden actually originate from all around the
world, finding out which ones will grow happily in your garden
depends on a few factors. 'cold hardiness' is one of
them.
|
| A
plants hardiness is determined by its capabilities of withstanding
low temperatures. |
| Any attempt to
categorise hardiness must be seen
as a guide only, much will depend on the plants individual environment. |
| UK
Hardiness Terms |
| Hardy
(to -15°C /5°F) |
| Frost
Hardy (to -5°C/23°F) |
| Half
Hardy (to 0°C/32°F) |
| Frost
Tender (to 5°C/41°F) |
|
|
| The US Department of
Agriculture has devised a zone scheme to identify the zone in your
area. These different temperatures are then divided up into zones as
follows. |
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|
Certain
measures may be taken to improve the likelihood of a plants survival
during cold periods. Plants that can be damaged by cold winds need
protection in the form of wind-breaks (natural or man made) e.g. trees,
hedging, walls,
fleece,
cloches,
cold
frames, plastic
greenhouses etc. Providing plants with free
draining soil prevents the growing point and roots from freezing. A
winter mulch is another way, a good mulch can be made from compost,
manure, gravel, bark etc.
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|
Some non-hardy varieties need
to brought indoors for the winter or stored in a frost free greenhouse. Always check the label of plants before buying, if
buying online most retailers show the plants hardiness.
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|
| UK
Equivalent USDA Zones |
|
Zone |
°C |
°F |
| 6a |
-23.3
to -20.6 °C |
-10
to -5°F |
| 6b |
-20.5
to -17.8°C |
-5
to 0°F |
| 7a |
-17.7
to -15 °C |
0
to 5 °F |
| 7b |
-12.2
to -9.5 °C |
10
to 15 °F |
| 8a |
-14.9
to -12.3 °C |
5
to 10 °F |
| 8c |
-9.4
to -6.7 °C |
15
to 20 °F |
| 9a |
-6.6
to -3.9 °C |
20
to 25 °F |
| 9b |
-3.8
to -1.2 °C |
25
to 30 °F |
| 10a |
-1.1 to 1.6
°C |
30
to 35 °F |
| 10b |
1.7 to 4.4 °C |
35
to 40 °F |
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|
| 2006 AGM
Plant Hardiness Rating |
 |
Plants
with an AGM (Award of Garden Merit) symbol
are labeled with the following hardiness
ratings. The hardiness rating is an integral
part of the AGM, and should be included in any
citation of the award. This is intended to serve
as a general guide to growing conditions, and
should be interpreted as follows: |
|
|
H1 |
Requires
heated glass |
| H1+3 |
Requiring
heated glass; may be grown outside in summer |
| H2 |
Requires
unheated glass |
| H1-2 |
Intermediate
between H1 and H2 |
| H2-3 |
Intermediate
between H2 and H3 |
| H3 |
Hardy
outside in some regions or particular situations or which,
while usually grown outside in summer, needs frost-free
protection in winter (e.g. dahlias). |
| H3-4 |
Intermediate
between H3 and H4 |
| H4 |
Hardy
throughout the British Isles |
| For plants requiring heated glass, further guidance is given as follows: |
Minimum temperature
(oC)
15: Hot glasshouse
10: Warm glasshouse
2: Cool glasshouse |
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