Agriculture Reference
In-Depth Information
Climate in Britain and Ireland
Differences in climatic conditions do occur across the
whole of Britain and Ireland. The differences are not
as great as those described above for world climatic
zones, but are enough (especially during the winter
months) to cause serious damage to certain plants
growing outdoors. For this reason, plants have, over the
years, been classified according to their temperature
sensitivity ( hardiness ) using different systems.
An American ( USDA ) system has been used for
several years in Britain and Ireland and is described
briefly on the companion website: www.routledge.
com/cw/adams.
Hardiness
The current Royal Horticultural Society hardiness list
gives nine hardiness ratings for plant species based
on growers' experiences of species planted in Britain
and Ireland. The RHS system can give a fairly accurate
indication of a plant's likely survival under Britain
and Ireland conditions, although variables such as
'condition and age of the plant' and 'position in the
garden' may influence its survival. When the RHS are
considering a plant species' eligibility to be awarded
an ' RHS Award of Merit ', its hardiness is carefully
assessed as part of this process. As a consequence,
all 'Award of Merit' species and cultivars are given one
of the nine 'H' ratings.
In Table 2.1, several examples of plant species in each
'hardiness category' are included, along with their area
of origin. The temperatures referred to are the lowest
winter temperatures tolerated (not the mean low
temperature measured over an extended period).
Figure 2.10 Lavandula species (lavender), with an H4
hardiness rating, originates in the Mediterranean area
Figure 2.11 Clematis armandii , with an H5 hardiness
rating, originates from China
Figure 2.9 Begonia a genus with an H2 hardiness
rating, originating from South America
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