| 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.
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A
plants hardiness is determined by its capabilities of withstanding
low temperatures. |
| Hardy
(to -15°C /5°F) |
| Frost
Hardy (to -5°C/23°F) |
| Any attempt to
categorise hardiness must be seen
as a guide only, much will depend on the plants individual environment. |
| Half
Hardy (to 0°C/32°F) |
| Frost
Tender (to 5°C/41°F) |
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| 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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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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| 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 from 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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| There are far fewer
zones in both the European hardiness ratings because most places in
Europe where people grow plants fall within US Hardiness Zones 6 to
10. |
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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 |
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