For your winters with hard frosts
With global warming, on the Atlantic coast, in the south of Europe and on Mediterranean islands, the choice of hardy exotic plants that can be adapted to our gardens is growing all the time. As a result, more and more of us are able to dream of an exotic garden.
The varieties in this category are semi-hardy exotic plants and can all cope with frosts of limited intensity and duration.
They include fruit trees such as the Toad Tree, climbers such as the Corkscrew vine and exotic bedding plants such as the African Iris plant.
But beware, you'll often be flirting with the hardiness limits of these splendors, so you'll need to be careful.
Indeed, the concept of plant hardiness is often misunderstood, and this can have dire consequences in our gardens.
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How to interpret the hardiness of exotic plants?
Hardiness of plants, definition
Hardiness refers to a plant's ability to withstand cold and frost.
A plant that can withstand frosts below -15°C is considered very hardy; one that can withstand frosts between -15°C and -8°C as moderately hardy; and one that can withstand frosts between -7°C and -2°C as not very hardy or semi-hardy.
Know your hardiness zone
To determine the hardiness of your region, refer to a USDA map.
In the regions mentioned in the introduction (with the exception of mountainous areas), the hardiness zone, or USDA zone, varies between 9A and 10B.
But here's where things get complicated: hardiness is only an assessment for mature specimens and can be influenced by factors such as sunshine (exposure), wind, rainfall and soil quality.
Knowing how to interpret the specifics of one's terrain
Choosing the right exposure
Obviously, cold-hardy exotic plants will prefer a sunny exposure. Choose southern or western exposures. In the event of frost, an east-facing exposure, with its early morning sun, brings too rapid temperature changes. To put it simply, a hardy tropical plant will prefer to recover gradually from overnight frost.
Beware of the wind
And yes, cold-hardy fruit trees like the Surinam cherry tree are like us, sensitive to wind chill. When playing with hardiness limits, it's therefore vital to plant in sheltered areas!
Know your soil
Few plants thrive in clay soils. Tropical plants are definitely not one of them!
A draining, permeable soil is preferable. The more your region is subject to heavy winter rainfall, the faster your soil will need to evacuate water.
Some varieties, like Cockspur coral tree, are particularly sensitive to excess water in the soil as soon as temperatures drop. When young, they will fail at temperatures well above their hardiness.
So don't hesitate to lighten your substrate as much as possible when planting.
Similarly, a trough-shaped plot offers little opportunity, whereas a slope or small hill for a bed is ideal.
As you can see, depending on the specifics of your terrain, you may be able to gain a few degrees on the hardiness communicated for a variety, or, on the contrary, you may have to subtract a few.
After careful consideration, you can choose the varieties that will adorn your garden.
How to protect your exotic plants outdoors
Install mulch at the foot of your plants
Mulching is always a good idea to help cold-hardy exotic plants get through the cold season as serenely as possible. It should be spread in a thick layer at the foot of the plants, preferably vegetal (hemp, cocoa husks, buckwheat hulls, crushed fruit stones...) so that, in addition to its protective function against the cold, it decomposes and gradually amends your soil. Mulching also has the advantage of limiting soil compaction by protecting it from rain, snow and wind, thus promoting microbial life and root aeration. Beware, however, of mulching with pine bark, which can acidify your soil.
Put up winterizing veils during periods of frost
If the nights are shaping up to be very cold, consider protecting certain cold-hardy exotic trees with a wintering veil. This should be spread over the entire aerial part of the plant, taking care that the textile does not come into contact with it. You can support it with stakes, for example, as it conducts cold and moisture. But beware: wintering veils prevent the plant from breathing and ventilating properly and encourage fungal diseases that could take advantage of this excess humidity to develop. They should therefore only be installed for a short period, to compensate for a few days of heavy frost; they should then be removed as soon as temperatures return to positive, or a few hours of regular aeration should frost persist.
When to plant exotic plants outdoors?
In most regions, outdoor planting should be carried out as soon as possible after the last frosts, and as carefully as possible (choice of location and soil preparation) to give it time to acclimatize before the first frosts. Only regions with milder winters will prefer late summer planting.
For young tropical plants like those offered by Rayon de Serre, please be patient!
The hardiness given is that generally accepted for mature specimens. With the exception of bedding plants, it is always preferable to grow them in pots for a few years. Above all, remember to keep your pots frost-free over winter, and to mulch and insulate the base of your pot.