Tender plants: where to place them to protect them effectively from the cold?

Which plants are affected?

The term “frost-tender plants” refers to several different types of plant.

1. Greenhouse plants, such as Hibiscus rosa-sinensis or most of our plants grown indoors. These are often exotic plants requiring a fairly high, constant temperature throughout year. Many of them cannot tolerate exposure to temperatures below +10°C. Often grown in pots, they can be moved outdoors only during fine weather.
2. Frost-sensitive plants. These are plants that cannot withstand any sub-zero temperature. Examples include the red frangipani, the Japanese pepper tree or Acalypha chenille. Also worth mentioning are citrus trees, since most fruit cannot withstand frost. They must be brought under cover before first risk of frost, usually in autumn.
3. Less hardy plants. They can tolerate frost, but only if it is short-lived and mild. They are generally tolerant between -1 and -6°C. Examples include many summer bulbs, some banana trees, abutilon, Strelitzia or bird of paradise, and many Fuchsias.

Indoor plants (here a Monstera), frost-sensitive plants such as many exotics (here a frangipani) and certain perennials are very frost-tender.

Provide frost-tender plants with favourable exposure

This is the first thing to consider. Choice of aspect is crucial, as perceived temperature can be very different between an area facing North and an area facing South within the same garden. Tender plants should ideally be placed in the warmest, sunniest corners, which face South or West.

However, note that although tender plants often welcome heat, they do not all tolerate the sometimes scorching exposures in the height of summer, especially in southern regions. In that case, best is to plant them beneath a deciduous tree: they will benefit from plenty of light from late autumn through spring, when temperatures are lowest, and from a more filtered, semi-shaded aspect in summer. You can also choose a South-East aspect, which will be a little gentler (morning sun is less fierce than afternoon sun).

Plant in suitable, well-drained soil

Soil quality is also essential for growing frost-tender plants. Most do not tolerate heavy soils, which become saturated with moisture in winter and make conditions feel even colder. Although some plants are theoretically fairly hardy, excess winter water can be fatal. This is the case for many Mediterranean plants, such as the lavender or the rosemary.

If your soil is clayey or compacted, it is imperative to work it before planting and add draining elements: river sand, clay pebbles, gravel, pumice, etc. You can also choose to create a mound, which will naturally allow water to drain away from the roots rather than stagnate. By contrast, avoid placing a frost-tender plant in a hollow or at the bottom of a slope.

Plants like rosemary need particularly well-drained soil

Choose a location sheltered by buildings

Especially if you grow frost-tender plants north of the Loire, it is preferable to choose a sheltered position, meaning north or east winds, the coldest, will be filtered or broken. Wind and draughts can indeed dry out aerial parts of plants, making them more vulnerable. Above all, strong wind will further reduce perceived temperature.

For this, you can use existing structures: a spot against a wall, under a terrace, on a balcony, next to a garden shed, etc. Stone walls have the advantage of storing heat during the day, then releasing it at night, when it is colder.

House walls prove very effective at sheltering the most vulnerable plants

Create a protected area

But beyond making use of existing structures, you can also recreate a sheltered spot. To do this, plant a hedge, install a trellis on which a climbing plant can grow, or create a living barrier (dead hedge, wattled wooden border, etc.).

Other measures to protect frost-tender plants from the cold

Install mulch

Mulch creates a protective insulating layer that helps combat cold. It will also generate a little heat as it slowly decomposes. Use plant husks, hay, leaf litter, RCW, etc. Apply in a thick layer of around 8 to 10 cm at the base of frost-tender plants.

Insulate potted plants from soil

To better protect frost-tender plants grown in pots, place containers on a brick or wooden block to insulate them from soil. Remember that plants in pots are naturally less cold-hardy, because the amount of soil is more limited. It therefore provides less insulation to the root system than when grown in the ground. Also consider grouping frost-tender plants to create a slightly warmer microclimate favourable to the plants.

Add winter protection

Finally, if you want extra protection for frost-tender plants, it is possible to install winter protection to shield them from cold. Fleece or covers are easy to find and fit. Just make sure not to press them against above-ground parts of the plant and plan to ventilate regularly when temperatures rise, to reduce risk of disease and drying out.

Protective covers, grouped plants and mulch: a winning trio for the most frost-sensitive plants in winter

Plant frost-tender plants at the right time

Unless you live in an area with a mild climate, where winters are short and frosts light, it is preferable to plant frost-tender plants in spring. Ideally, wait until the last risk of frosts has passed, for example after the Saints-de-Glace in northern regions or mountain gardens.

Manage watering properly

Even though most plants are in dormancy during winter, they may still need watering. Frequency should be adjusted according to the weather. In absence of precipitation, watering every 3 to 4 weeks is generally sufficient. However, never water before a forecast frost or a snowfall event.