AREC-Monticello Research Report BB 90 2
ASSESSMENT OF FREEZE DAMAGE TO
COLD HARDY CITRUS AT THE AREC-MONTICELLO
Peter C. Andersen and Gary W. Knox Library
Agricultural Research and Education Center JUL 9 199
Monticello, Florida / Uniersity of orida
Prior to the 1980's it was not unusual to see maturii"' specimens
of cold hardy Citrus cultivars in north Florida. Three major
freezes in the last decade have all but eliminated Citrus north of
30.50N latitude. Nevertheless, many horticultural enthusiasts are
* apparently optimists by nature since cold hardy Citrus cultivars
are being sold with regularity in north Florida. The purpose of
this report is to describe the 1989/1990 winter freeze damage to
Citrus and Citrus relatives at the AREC-Monticello.
A 0.5 acre planting of Citrus was established in 1986 at the
AREC-Monticello. The site has a Fuqua fine sand soil and is
exposed with a slight slope providing good air drainage. The
plants (Table 1) were randomly arranged in 4 rows oriented north to
south with 15 feet between plants and 20 feet between rows. The
plants were planted from 3 gallon containers into the existing
centipede/bahia turf, leaving a 4-foot diameter circle of bare soil
around the trunk of each plant. Trees were fertilized with a 10-
10-10 product applied at rates of 1/2 lb. per plant in 1986 and
S1987, 1 lb. per plant in 1988 and 1989, and 2 lb. per plant in
1990. Plants were irrigated with an overhead irrigation system as
needed. Each autumn, soil was mounded around the trunk of each
plant to a height of 1.5 feet. All cultivars were grafted on
trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstocks.
Trees were in the process of regrowth following minor freeze
damage during the winters of 1987 and 1988. On 22 December 1989,
an arctic cold front penetrated the southeastern United States, and
the AREC-Monticello recorded a high of 340F and a low of 240F. On
23 December, a high of 310F and a low of 120F occurred; on 24
December, a high of 360F and a low of 160F were recorded. Ponds and
small bodies of water in north Florida remained frozen for up to 5
days. High winds and low temperatures prevented the use of
S overhead irrigation for freeze protection of Citrus.
All Citrus species and relatives sustained severe cold injury
(Table 2). With the exception of one specimen of kumquat, all
exposed wood was killed. Cold tolerance was denoted by regrowth
from the portion of trunk that was mounded with soil. Minimum
temperature tolerance reported by Krewer and Powell (Table 2)
before significant damage occurs is generally in agreement with the
results obtained at the AREC-Monticello.
Based upon these results it appears that no Citrus species or
relatives have sufficient cold hardiness for north Florida unless
special precautions are taken. 'Meiwa' kumquat, 'Owari' satsuma,
'Chinotto' sour orange and 'Changsha' mandarin can likely be grown
with some success in north Florida if winters are less harsh, as
was generally the case before 1980, or if adequate cold protection
methods are used. 'Duncan' grapefruit, 'Meyer' lemon, 'Navel'
orange or 'Sunburst' tangerine all lack sufficient cold hardiness
to be grown in north Florida.
Practices that would minimize the extent of cold injury to
Citrus species and relatives include: 1) plant trees on the south
side of the house or provide a windbreak on the north and west
sides of the tree to minimize exposure to the north winds that
typically accompany cold weather; 2) insulate the trunk by using
tree wraps, utilizing microsprinkler irrigation during cold
weather, or mounding trunks with soil to a height of at least 1.5
feet, and; 3) avoid fertilization after 1 July to prevent
succulent regrowth that is more susceptible to cold injury. Many
people have successfully grown satsuma trees in north Florida by
providing a portable shelter for winter protection. Also keep in
mind that young trees are more susceptible to cold injury than old
Table 1. Citrus species and relatives planted at the AREC-
Monticello in 1986.
Scientific Name and Cultivar
Citrus reticulata (Blanco) 'Owari'
Fortunella margarita x japonica 'Meiwa'
Citrus myrtifolia (Raf.) 'Chinotto'
Citrus unshiu (Marc.) 'Changsha'
Citrus paradisi (Macf.) 'Duncan'
Citrus meyeri (Y. Tanaka) 'Meyer'
Citrus sinensis (Osbeck) 'Navel'
Citrus sinensis (Osbeck) 'Sunburst'
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