What is the orange zone?

Why the orange tree?

Citrus trees are renowned for being frost-sensitive and not very hardy, originating from the tropical and subtropical regions of Asia: they require plenty of sunlight and warmth to thrive and produce fruit sustainably and regularly. They are generally considered unable to withstand negative temperatures, and they begin to suffer from the cold below -5/-10°C. This is why they can only be grown in the ground in our warmest regions.

In France, most Citrus are cultivated mainly along the Mediterranean coast, in the French Riviera and Corsica, in the area known as the “orange zone.” The sweet orange (Citrus sinensis) particularly thrives in this climate where it finds the warmth it needs all year round. This citrus tree is therefore used as a “benchmark” to define the preferred climatic zones where temperatures do not drop below a certain threshold, and where the cold is unlikely to jeopardise its cultivation.

Orange trees in the ground, a cultivation possible only in certain areas of France

Where is the orange tree zone located?

The so-called orange zone corresponds to regions where orange trees (and other citrus trees) can be grown in the ground without risk. This takes into account their maximum cold tolerance threshold, that is to say, their hardiness. The USDA (United States Department of Agriculture) has defined a system of geographically delineated hardiness zones. This system, known as the “USDA system,” has been adopted in many countries. This geographical division is based on the average lowest temperatures over the past 20 years in a given territory. Globally, there are now 13, or even 14, hardiness zones.

In France, there are 10, ranging from -23.3 to -20.6°C in mountainous areas (USDA zone 6a) to 1.7 to 4.4°C (USDA zones 10a and 10b) around the Mediterranean Sea. The higher the number, the milder the annual minimum temperatures indicated. They are further subdivided and noted with an “a” or “b.” The orange tree is classified in zone 9a, meaning it can be planted in the ground in a large part of the Mediterranean coastline, particularly in the Côte d’Azur, especially in Menton and Corsica, where the lowest recorded temperatures range between -6.7 and -3.9°C.

However, it is also possible to consider planting in intermediate zones located between the Côte d’Azur and Perpignan:

• 8a, 8b: zones where the lowest recorded temperatures range from -12.2°C to -6.7°C, specifically on the Atlantic coast (Pyrénées-Atlantiques) and in Brittany
• 9B: in regions of the “South-West Basin” (Aquitaine, Languedoc) where the minimum temperatures range between -3.9°C and -1.1°C.

Proof that the orange zone is expanding… In reality, thanks to successive grafts and climate warming, citrus trees are now being seen in other zones, notably in Bordeaux, Quimper, Saint-Brieuc, and on the Cotentin peninsula! Other factors must also be taken into consideration. Wind, in particular, amplifies the effects of cold on plants: a sunny spot in a well-sheltered garden can allow the most delicate plants to acclimatise.

However, the mildness of recent winters should not make us forget that even in the most sheltered zones, one is never safe from a polar wind from the North!

Today, we can grow lemon trees outside the Mediterranean coastal fringe…

→ Discover all the characteristics of these climates in our sheet on USDA zones in France

For which plants?

Beyond citrus trees, the orange tree zone is reserved for all plants with limited hardiness, including bushes thriving in Mediterranean climates and certain Mediterranean perennial plants, which should be avoided in regions with excessively cold winters or too frequent summer rains.

Discover our selection of suitable plants!

Oleander, mimosa, bougainvillea, and many other plants are known to be frost-sensitive