Citrus hardiness, which species survive as it freezes and gets colder

Often grown in our regions, citrus trees don’t all react to freezing the same way.

This depends mainly on the variety itself, but how they’re being grown also has an impact on their frost resistance.

The most important factor is the variety that’s being grown. Secondary factors are also relevant: how old the tree is, how old its organs (branches) are, when it freezes and how long the frost spell lasts.

How long the freezing lasts

A short bout of frost, shortly before dawn, with a nice warm sunny day and above-freezing temperatures shouldn’t lead to any problems at all. This is true as long as the temperature didn’t drop below the threshold known for each variety, listed lower down in this article.

Leaves turn brown and curl back while staying on the stemHowever, if the freezing lasts for several days or even weeks, the tree may truly be in danger: citrus trees can only stay dormant for short while, after that they start dying.

A healthy citrus that’s well-settled in will resist frost much better than a young one, or one that’s weak because of a disease or pest.

This is the reason many treatments are sprayed preemptively just before winter, against scale and aphids for instance.

Symptoms of freezing on a citrus:

Fruits turn soft, necrosis appears, and sometimes they burstA frozen citrus tree has telling symptoms: its leaves fall over and dry out, but they still cling to the tree.

Frozen fruits are easily identifiable: they’re soft instead of firm, and may show signs of necrosis or even burst open. Bark on branches cracks open.

What to do if it freezes?

If your citrus has already frozen over, and if some portions only of your citrus show the symptoms above, then you must go for a drastic pruning of all dead branches and any branch which has burst bark.

Also remove all fruits, because they would infect the tree with diseases if they’re allowed to rot on the tree.

Only perform this pruning at the end of winter (when the vegetation phase begins again).

If even just a small portion of the tree didn’t die, then there’s a chance that the citrus may survive.

Even so, and even if the citrus tree seems to come back to life, it will stay very fragile and will have trouble producing fruit.

Growing citrus outdoors

Growing citrus in the ground, outdoors, is only possible in areas where temperatures never drop below freezing. This isn’t the case anywhere in the British Isles, nor in Northern States in the USA.

Non-freezing  regions in Europe and North America are:

  • Coastal areas along the Mediterranean, Iberian peninsula, Gulf of Mexico, California coastal areas.
  • Southern states in the USA, at relatively low altitudes: California, Florida… and even Texas, if not too far inland.
  • These areas can welcome certain varieties, even directly in the ground (kumquat, mandarin orange, satsuma).

Take note, though, that all these areas aren’t necessary frost-free all year round: you’re still running a risk of losing the trees if not protected.

Indeed, for example, along the Mediterranean ocean, cold winters in 1985 and 1986 devastated a great number of citrus trees that were growing outdoors. Many magnificent lemon trees and orange trees never recovered and were lost.

Potted citrus tree in winter

Calamondin planted in a pot to be more easily brought indoors against the coldFor potted citrus, it’s best to bring them indoors in a place that has none or little heating. Such places used to be called “orangeries”, they’re the ancestors of today’s greenhouses.

Temperatures of around 40°C (4 to 6 degrees Celsius) are perfect to protect citrus during winter.

Care in this situation:

A lean-in near a South-facing white wall where citrus are grown. The lean-in can be covered with greenhouse tarps.During the rest phase, you must keep a watchful eye on the health of your citrus plants. In particular, scale insects tend to particularly love wind-free, sheltered places.

You can treat citrus trees even in winter if they’re in a sheltered spot: what matters is that the temperature doesn’t freeze.

If you can’t move your pot around, you’ll have to make do with protecting it with some sort of thermal insulator. Bubble wrap works fine if that’s all you’ve got.

Winterizing fleece:

For the branches, it’s best to use winterizing fleece. This is a product that makes your plant feel that it’s 3 to 4 degrees warmer than the air outside it.

  • Citrus tree with winterizing fleece to protect it from the coldIt’s important to remove the fleece whenever possible: this helps renew air around the plant, which matters since it’s still breathing.
  • As soon as the last frost date has passed, remove the fleece immediately.
  • Young citrus are more vulnerable to freezing, so be especially vigilant if you’re working with young plants.

Read also: how to winterize your plants

Hardiness of citrus varieties and frost resistance

Here is a table that’s ordered by frost vulnerability. The most fragile and vulnerable ones are at the top, the hardiest ones at the bottom. This only includes the most easy-to-find varieties.

>> Learn about the different citrus varieties <<

Take note that the temperatures below are for the tree itself, not the fruits: fruits will freeze much earlier than shown below.

In addition, the temperatures below are for trees that are well-settled in, vigorous outdoor growers that are 5 to 6 years old, without any diseases or parasites that might weaken them.

  • Mexican lime or key lime: (Citrus x aurantifolia): 26°F or -3 °C.
  • Persian lime or Tahiti lime: (Citrus x latifolia): 25°F (-4 °C). Tends to lose leaves in case of strong winds and low temps. Used for punch and for perfume.
  • Citron, hand of Buddha: 25-26°F (-3 to -4°C). Hand of Buddha is used in fruit jams and jellies.
  • Limequat: 25-26°F (-3 to -4°C).
  • Bergamot tree: 21-23°F (-5 to -6°C). Bergamot is used in making perfume, bergamot tea, and as a flavor for candy.
  • Lemon tree: 21-23°F (-5 to -6°C). Including the 4 seasons lemon tree
  • Calamondin: (indoor orange tree) 21-23°F (-5 to -6°C). Note that variegated calamondino isn’t as hardy, only 23-25°F or -4 to -5°C.
  • Combava or makrut lime (kaffir lime): 23-25°F (-4 to -5°C). Fruit and leaves are a spice in cooking.
  • Grapefruit tree, the original tropical species Citrus maxima): 19-21°F (-6 to -7°C).
  • Clementine tree: 17 to 19°F (-7 to -8 °C). (All you need to know about the clementine tree).
  • Common mandarin orange tree: 17 to 19°F (-7 to -8 °C) (growing this one? here!)
  • Orange tree: 17 to 19°F (-7 to -8 °C).
  • Pomelo: (Citrus paradisi): 17 to 19°F (-7 to -8 °C). The ‘Star ruby’ pomelo variety produces pink-flesh fruit.
  • Bitter orange: 16°F (-9°C). Used in perfume, and a key ingredient of Cointreau and Grand Marnier spirits. Also delicious in orange marmalade and simply beautiful as an ornamental tree.
  • Satsumat mandarine orange: 10 to 14°F (-10 to -12 °C). Fruits freeze at 25°F already (-3 to -4°C).
  • Kumquat: 10 to 14°F (-10 to -12 °C). Fruits freeze at around 25°F (-3 to -4°C).
  • Yuzu: 5°F, about -15°C. Superior taste of its leaves, fruits aren’t as impressive. More about growing yuzu.
  • Poncirus trifoliata: -4°F or -20°C. The only citrus with deciduous foliage.

Some parts of the tree are more vulnerable to freezing, like young stems, flower buds and fruits, but larger, older branches will survive freezing.

Philordi


Image credits (edits Gaspard Lorthiois):
CC BY 2.0: Maxim Massalitin
Bugwood.org: Gerald Holmes
CC BY-SA 2.0: Jihad Alachkar
Pixabay: FinjaM, Jessica Bolander