Agriculture Reference
In-Depth Information
Table 2.1
Royal Horticultural Society hardiness categories
Category
Hardiness rating
Species examples
H1a
Tolerate a temperature as low as +15ºC. Require a heated
greenhouse, or grown as a house plant.
Begonia rex
(Brazil),
Dieffenbachia seguine
(tropical South America), and
Anthurium
andraeanum
(Ecuador)
H1b
Tolerate temperatures as low as 15 to 10°C. Subtropical to tropical
plants; need heated glasshouses or grown as a house plant. May be
placed in sunny positions outdoors in summer.
Hibiscus rosa-sinensis
(from southern China) and
Monstera deliciosa
(from Mexico)
2
H1c
Tolerate temperatures as low as 10 to 5ºC. Subtropical plants need
a heated glasshouse. Can be grown outdoors in summer throughout
most of Britain and Ireland while daytime temperatures are high
enough to promote growth.
Most bedding plants such as
Pelargonium zonale
(South Africa) and
Solenostemon scutellarioides
(Malaysia). Also, tomatoes (Central America) and
cucumbers (China)
H2
Tolerate temperatures as low as +5 to +1°C. Ornamental
species are often grown in frost-free glasshouses. Tolerate lower
temperatures, but cannot tolerate any freezing conditions. May
survive outdoors in frost-free town locations, or near the coast.
Grown outdoors when risk of frost is over.
Originate from warm-temperate and subtropical
zones, such as
Canna
spp. (South America),
Begonia x tuberhybrida
(Peru),
sweet corn
(Central America) and potatoes (Peru)
H3
Tolerate temperatures as low as +1ºC to -5°C. Half-hardy, often
grown in unheated glasshouse. Survive mild winters, outdoors.
Often considered hardy in coastal/mild areas (except in hard
winters). May also be hardy elsewhere when protected by a wall.
Warm temperate plants such as
Cosmos
bipinnatus
(Mexico),
Osteospermum jacundum
(South Africa) and
Papaver somniferum
(southern
Europe). Spring-sown vegetables such as carrots
H4
Tolerate temperatures as low as -5 to -10ºC. Hardy in average
winters, and throughout most of Britain and Ireland (except for frosty
inland valleys, or at altitude, or in central/northerly locations). May
suffer foliage damage and stem dieback in harsh winters in cold
gardens. Some normally hardy plants may die in long, wet winters in
heavy or poorly drained soil.
Plants in pots
are more vulnerable.
Many herbaceous and woody plants such as
forget-me-not (
Myosotis sylvatica
from Europe),
lavender (
Lavandula x chaytoriae 'Sawyers'
from
Mediterranean area). Winter brassicas (from
N. Europe) and leeks (from the Mediterranean
region)
H5
Tolerate temperature as low as -10 to -15°C. Hardy in cold winters,
and in most places throughout Britain and Ireland even in severe
winters. They may not withstand open or exposed sites or central/
northern locations. Many evergreens suffer foliage damage, and
plants in pots will be at increased risk.
Herbaceous and woody plants, such as
Aucuba
japonica
(Japan),
Clematis armandii
(China) and
Filipendula rubra
(east and central USA)
H6
Tolerate temperatures as low as -15 to -20ºC. Hardy in very cold
winters across Britain and Ireland and northern Europe. Many plants
grown in containers will be damaged unless given protection.
Acer palmatum
(Japan),
Chaenomeles x superba
(China),
Clematis tangutica
(China) and
Heuchara
cylindrica
(western USA)
H7
Tolerate temperatures colder than -20°C (
very hardy
). Such species
are hardy in the severest European continental climates including
exposed upland locations in Britain and Ireland.
Larix deciduas
(northern Europe),
Cornus alba
(northen China), and
Erica carnea
(central
Europe)
The new RHS hardiness ratings are listed for a wide
range of plants on the companion website: www.
routledge.com/cw/adams.
sending collectors around Africa 2,500 years ago in her
search for frankincense (
Boswellia carterii
). The Greek
philosopher Theophrastus (
c
. 310
BC
), a contemporary
of Aristotle, recorded exotic species such as bamboo,
banana, pepper, cinnamon and cotton brought into
Greece from Asia in 323
BC
by Alexander the Great's
army.
The Chinese emperor Ch'in (
c
. 200
BC
) who began the
construction of 'the Great Wall' is recorded as having
directed the collecting of some 3,000 species of
various herbaceous and woody plants for his gardens
near Xian. The Roman writer Pliny the Elder (
c
.
AD
40)
referred to eastern non-indigenous species such as
apples, pears, cherries and cucumbers being grown
in Rome. Dioscorides (
AD
40-90), a doctor in Rome,
described over 600 medicinal plants. Some of these
such as pepper, ginger and aloe had been brought in
from other areas of the world.
Plant collectors
Many settled cultures throughout human history
have improved local wild plant species for their own
use and enjoyment. In addition, there have been
remarkable
botanists
and
explorers
who travelled
widely around different regions of the world to
collect promising plant material to grow in their home
area. Evidence for such activity in earlier cultures is
sparse, but some topics written two thousand years
or more ago indicate that important species had
been introduced by that time. Chinese botanists are
recorded as collecting rose species for breeding 5,000
years ago. In Egypt, Queen Hatshepsut is listed as
