How to protect plants from snow

Over the last decade, winters have brought milder average temperatures and less snow than we are used to seeing, but this doesn’t mean that cold snaps are a thing of the past. Although on the one hand, milder weather enables various plants, including delicate species, to survive more easily in the garden, on the other hand, cold spells are necessary. Low temperatures allow plants to grow thanks to the bud cycle, with “pause” mechanisms that preserve them from cold and frost — otherwise known as dormancy, quiescence and other states of suspended growth — which is followed by vegetative awakening as temperatures increase. These mechanisms are part of the adaptation strategies that plants adopt to overcome unfavourable winter conditions.

The risk of a mild winter is therefore that some plants whose buds have resumed growth activity will suffer damage from cold snaps, icy winds or late frosts. Or, if temperatures have been insufficiently cold, plants may sprout late or poorly, or may even shed the buds themselves. Furthermore, cold weather gives plants respite from parasitic attacks and diseases. In this article, we look at why the cold can be crucial for vegetation and how to protect plants from frost.

Snow and frost: their effects on plants

While low temperatures benefit plants to some extent, it is also true that cold can be a problem. Frost forms when the air temperature drops to 0°C or below, whereas snowfall typically occurs from freezing point up to an air temperature of 3°C.

Cooling and freezing are forms of stress that plants experience due to low temperatures. How they cope with this stress depends on the species and variety, their state of health, the presence or absence of protections (which we will talk about later), the rate and duration of the drop in temperature (sudden drops are more harmful) and so on. Plants are able to adapt and resist up to a certain point, but from 15-10°C down to 0°C, they are prone to damage (such as the slowing of their functions). Below freezing point, they suffer from frostbite (resulting in the formation of ice in tissues, dehydration and breakage). Plants originating from warm areas suffer more and have lower adaptability than species endemic to temperate or continental climates, or in any case, native plants.

So, to protect the plants in your garden from the cold, the first thing to do is “classify” them according to the minimum temperatures they can tolerate, which depends on the species/variety and age (young plants are more sensitive). We suggest classifying them into the following plant categories:

• Very delicate: able to resist down to 15°C, i.e. succulents.

• Delicate or semi-hardy: can tolerate temperatures down to 5-6°C, i.e. typical Mediterranean species (olive, rosemary, lemon, etc.).

• Hardy: can withstand temperatures down to -5°C or less, such as roses and other flowering shrubs, hedge shrubs, conifers and – despite their Mediterranean origins – oleanders.

Snow predominantly damages the foliage of plants, by remaining on leaves and branches for a long time and thereby creating the conditions for cooling/freezing. If the snow is heavy and doesn’t slide off onto the ground, its weight can overload and break branches – especially the longest ones – or warp them by bending them outwards: this also applies to hardy species, which are otherwise resistant to cold. Evergreens are most at risk as opposed to deciduous trees, which have a smaller surface area for snow to accumulate in, although the latter are disadvantaged by having generally less flexible branches. By contrast, when it comes to soil and the roots of plants, a thick layer of snow works as an insulator: by remaining at around 0°C in the layers close to the ground, it protects the snow from more frigid external temperatures.

How to protect plants in the open ground from the cold

To protect plants from the cold in the open ground of your garden:

• Cover the most delicate plants with non-woven fabric (NWF): it comes in sheets, which you can wrap around the aerial part (canopy), or practical, ready-made hoods.

• You can protect roots from frost and wind, which dry out the soil, by mulching at the foot of the plants with a generous layer of natural material (at least 8-10 cm thick).

• Suspend watering, but if the season is particularly dry, water evergreens moderately about once a month.

• Protect the plants most exposed to the wind, which exacerbates the effect of the cold, by wrapping them or creating a windbreak around them using bamboo screening.

By mulching natural material you can recycle waste generated from gardening work, including dry leaves collected with a blower, dried grass cut with a brushcutter, bark, and pruning debris shredded with a flail mower or bioshredder (find more tips in our dedicated article on how to mulch).

You can combine canopy protection with mulching. You may want to protect younger trees and shrubs in order to help them get through their first winter after planting. Also mulch flowerbeds with perennial herbs, which appear dead because they are dry or lack an aerial part. In reality they are dormant and the vital parts are at ground level (basal buds) or underground (bulbs, rhizomes etc.), waiting to regenerate the plant in spring.

How to protect potted plants from the cold

Protecting by means of non-woven fabric and mulching is an excellent solution even for potted plants, which, perhaps due to their weight, cannot be moved to sunny areas sheltered from the cold wind (such as in a porch) or, in the case of the most delicate species, to an enclosed and bright environment (such as unheated rooms in the house, a greenhouse etc.).

With non-removable potted plants, we also suggest insulating the container itself, for example by wrapping it in non-woven fabric, jute or bubble wrap and, if possible, separating it from the ground using a wooden board or polystyrene panel. Bear in mind that the roots of potted plants are especially vulnerable to the cold due of the reduced volume of soil.

When you are dealing with large weights and volumes, such as in the case of potted plants or flowerpots, you can make the job easier by relocating them in a transporter.

How to protect allotment vegetables from the cold

On your allotment you can safeguard your winter vegetables by building a cold tunnel on each plot, with galvanised iron arches for the load-bearing structure, covered by strong polyethylene or PVC sheeting. Alternatively, apply mulch using natural materials or plastic mulch sheeting. If you need to intervene urgently, or for additional protection under the tunnels, you can lay non-woven fabric sheeting directly on the plots.

Another important practice for protect the roots of plants is to make sure that the soil is well drained, i.e. that water does not stagnate. Water cools the soil and, in frosty conditions, it is liable to freeze. Potted plants are at greatest risk, and the smaller the container, the more likely they are to suffer damage from cold and frost. To facilitate soil drainage, in your vegetable patch we recommend that you raise the beds instead of keeping them at ground level (here you will find some ideas for organising the beds of your vegetable patch). Clay soil is known for its poor drainage: here's how to improve hard ground, including with the help of a rotary tiller or rotary cultivator.

How to protect plants from snow

NWF, which we talked about earlier, protects vegetation from the cold. It not only insulates plants from frost, but also prevents snow and ice from coming into contact with plant tissues. After gathering and tying the canopy, wrap the NWF directly around the canopy, or use it to cover a structure that provides a roof over the plant, built from bamboo canes or wooden stakes, for example. The canopy should be tied – with raffia, soft plant twine or similar – not too tightly so as to preserve twigs, leaves etc. and to allow air to circulate and prevent fungal diseases. If it snows frequently where you live, to protect your plants from the snow, make sure that the non-woven fabric protections for the canopy and the structures that it covers are steeply sloping if possible, so as avoid retaining snow.

As an alternative to non-woven fabric you can use plastic sheeting, but on sunny days be sure to fold it back during the hottest hours in order to avoid stagnating moisture and the spread of disease. Even though it is a breathable material, we still recommend that you fold back NWF covers in the same way.

Let's focus on the evergreen plants in your garden. Conifers such as firs, in addition to having rather elastic branches, have a pyramid-shaped canopy that enables snow to slide off it. If you prune evergreen hedges into a geometric shape – especially one where the top part is narrower than the base – the plant grows with a compact structure and in winter offers less surface area on which snow can accumulate. On evergreens with a dense canopy, such as young plants and hedges or bushes kept with a free-form shape, the weight of the snow tends to bend the branches outwards, moving them away from the trunk and thus distorting the plants. Therefore, if you live in a snow-prone area, we recommend that you gather the foliage together and tie it up, so that the snow has little space to rest on and slides easily onto the ground.

In the event of snowfall, remove it from branches, NWF and plastic plant protections, tunnel coverings in the vegetable patch, and so on. To do this, all you need is a broom to gently sweep the surfaces and/or shake the trunk to remove the white stuff from the highest branches. Avoid stepping on a snowy lawn, so that it doesn’t compact and freeze, thus damaging the grass tissues. Don’t use de-icing salt on your lawn, and if you spread it on your driveway, be careful around the edges where it could be scattered onto nearby grass and plants.

In the garden, winter is a fairly quiet period but – as we have seen – when temperatures drop, we need to remain vigilant. Here you find a summary of winter maintenance activities, including dry pruning to be done at the end of the season, which also rid plants of broken branches and parts "burned" by the cold, thereby remedying the damage caused by snow and frost. On that subject, we also offer you a guide to selecting pruning tools.