Before setting your sights on a particular palm species, it is absolutely essential to take into account certain selection criteria since this arborescent plant is intended for a cultivation in the ground. Choosing an outdoor palm tree is therefore not done lightly if you want it to benefit from excellent conditions to develop without problems. Let’s see which are the two points that you absolutely need to look into when buying a palm tree.
Choose an outdoor palm according to the climate
The climate is the most important criterion to consider before buying a palm tree to plant outdoors. Fans of the genre can be reassured: there are about 2,500 species. Whatever the region in which we live, there are therefore necessarily palm trees capable of adapting to it. To choose the right one, you have to find out about the hardiness of the species because not all palm trees tolerate frost. Fortunately, there are still some that easily resist very low winter temperatures.
Note that palm trees can be classified into three categories distinct, namely:
- rustic palm trees : they tolerate temperatures below -6°C,
- The moderately hardy palms : they are more suitable for cultivation in the southern regions of France as well as along the Atlantic coast,
- Non-hardy palms : they do not support negative temperatures and some can even be seriously in danger of death below 10°C, as is the case with some tropical palms.
It is therefore clear that if a very chilly palm can only appreciate the Corsican climate, for example, it must absolutely not be planted in a garden located in Lorraine.
In addition to the common temperatures in winter in your region, you must also consider the earliness of frosts, which can strike as early as November, the duration of frost periods, the frequency of late frosts, i.e. in April or in May. Finally, very humid winters are not to the liking of all palm trees either.
Types of climates and hardiness zones in France
here are the different types of climates in our countrythis being further divided into hardiness zones (from 6 to 10) or zones USDA (US Department of Agriculture to whom we owe this concept of geographical division). These zones were defined according to specific climatic conditions, namely the average, over the last 20 years, of minimum temperatures in winter. It is very interesting to keep these indications in mind when deciding to choose a palm tree.
- Type 1, mountain climate, Zone 6a: -23.3 to -20.6°C.
- Type 2, semi-continental climate and climate of the mountain margins, Zone 6b: -20.6 to -17.8°C.
- Type 3, degraded oceanic climate of the central and northern plains, Zone 7a: -17.8 to -15°C.
- Type 4, altered oceanic climate, Zone 7b: -15 to -12.2°C.
- Type 5, frank oceanic climate, Zone 8a (-12.2 to -9.4°C) and zone 8b (-9.4 to -6.7°C).
- Type 6, altered Mediterranean climate, Zone 9a: -6.7 to -3.9°C.
- Type 7, Southwest Basin climate, Zone 9b: -3.9 to -1.1°C.
- Type 8, frank Mediterranean climate (Corsican coast and extreme south-east), Zone 10a (-1.1 to 1.7°C) and zone 10b (1.7 to 4.4°C).
Gardeners are strongly advised to always refer to these various very precise databefore buying plants, especially if he lives in an area considered extreme in terms of climate.
Choose a palm adapted to the size of the garden
Some palms reach a moderate height in adulthood while others become gigantic within a few years. To maintain a certain consistency the dimensions of the tree must not be disproportionate to those of the ground. A palm tree should never be in the way.
As an indication, here are some examples of palm trees to plant outside. North of the Loire, it is possible to grow a palm that is very resistant to cold. Among the hardy palms that perfectly tolerate low temperatures, we find for example:
- A humble caller : a pretty bushy dwarf palm with a compact base, which measures in adulthood approximately 4 m width and height,
- Trachycarpus Fortunei : it is the palm of China nicknamed hemp palm, whose stipe (trunk) does not exceed 30 cm in diameter in adulthood, but this specimen still reaches a height of the order of 15 m,
- phoenix canariensis : it is the Canary Islands palm sometimes called false date very common on the Côte d’Azur. It should only be grown in areas where winter temperatures do not drop below -7 or -8°C. With an average height of 12,50 m and a wingspan of 8m, it can only be suitable for a large area garden.
- Washingtonia filifera : known as the California palm, it is also called the petticoat palm. Originally from Mexico, it has an interesting hardiness since it can withstand -12°C provided the soil is dry. It grows fairly quickly and reaches a maximum height of 17 to 18 m for a width of 5 m.
- Rhapidophyllum hystrix : it is the needle palm or porcupine palm. Very hardy, it braves temperatures of around -25°C without flinching. It forms a clump of about 1,60 m in height for 2 m in width at the most. It is therefore well suited to a small garden.
Of course, in our regions with mild winters, each gardener can choose any species of palm tree, but always taking into account its dimensions as an adult. In any case, when buying a palm, it is necessary to check with the producer that the desired species can indeed be planted outdoors in the USDA zone concerned.