Cold-Hardy Citrus for North Florida
Prior to the 1980's it was not unusual to see mature specimens of "cold-hardy" citrus in north Florida. Three major freezes in the 1990’s have eliminated most of the citrus north of 30.5 north latitude. Nevertheless, cold-hardy citrus are being sold with regularity in north Florida.
Homeowners should consider growing only a few of the many available citrus types. Of the three types of sweet citrus (mandarins, oranges and grapefruits) only mandarins have sufficient cold hardiness. Satsuma (Citrus reticulata) is the most popular mandarin in north Florida with cold-hardiness down to about 20F, although fruit damage can occur at 25F. It is self-fruitful and fruit ripen in October. Other cultivars such as Ponkan (mandarin), Clementine, Dancy and Robinson (tangerines), Lee, Page and Osceola (citrus hybrids) or Minneola, Nova and Orlando (Tangelos) can tolerate minimum temperatures of about 23-27F before tree damage will occur, and are best-adapted to areas south of Ocala. Another disadvantage of these cultivars, compared to Satsuma, is that fruit generally ripen during the winter and can be frozen at temperatures of 25-28F. Sweet oranges and grapefruit are even less tolerant of cold, and should not be grown much further north than Orlando.
Kumquats are the only acid type of citrus that are sufficiently cold-hardy for Tallahassee; lemons and limes will not tolerate our winters. Meyer lemon, a relatively cold-hardy lemon hybrid will tolerate temperatures down to about 26F. Meiwa, Nagami or Marumi kumquats (Fortunella x crassifolia), or the Changshou kumquat (Fortunella x obovata) will typically survive down to 20F.
Of the passive methods to minimize cold damage, proper site selection is most critical. Trees should be planted on the south side of homes or other structures, or windbreaks must be provided to minimize exposure to north or northwest winds. Also, citrus grown north of Ocala should be grafted on trifoliate orange (Poncirus trifoliata) rootstocks which confers a greater degree of cold hardiness to the scions than other rootstocks.
Cold damage can be minimized by following some annual cultural practices. Do not fertilize after July; a late application of fertilizer can stimulate a new flush of growth in the fall that is especially susceptible to damage. Also, each December the trunks of young trees should be insulated with a commercial tree wrap or mounded with soil at least to a height of 12 feet (young trees are more sensitive to cold than old trees). This protects the trunk so that even if the branches freeze back, the tree will be able to re-sprout from dormant buds on the trunk. Remove the wrap or mounded soil each spring. When temperatures below 25F are predicted, you may want to provide additional protection. A day prior to the freeze, thoroughly wet the soil around your trees. Wet soils retain more heat than dry soil and thereby provide a degree or two of protection. A method often used by people with only a few small trees is to place a portable shelter over young trees just prior to the cold weather. Placing an incandescent light bulb in the shelter will prevent winter damage under the worst weather conditions. The shelter should be removed during the late morning when temperatures moderate.
- Pete Anderson and Gary Knox, UF-IFAS, NFREC Quincy.