Preserving Plant Health in Cold Weather

By Libby Reeves

The weather seems to have taken a turn for the better as I sit in beautiful sunshine, not wearing a coat for the first time this year, with a smile on my face. The daffodils are popping, the snowdrops are in full bloom, the early flowering trees are budding up ready to flower and it feels like spring is here. But only a couple of weeks back it felt so very different. The ground would not thaw, the wind whipped across the nursery and my fingers burnt with frost.

There are gardens that are more affected by cold than others. Exposed gardens at the top of hills or that look out onto open fields can have problems as the wind whipping in can lower the temperature dramatically and remove the moisture in the air. Frost pockets are formed in lower sections of the garden where cold air will travel downhill and sit, causing that part of the garden to be particularly cold. North facing areas that have no direct sunlight never have the sun’s rays to warm them, and east facing areas get sunshine in the morning often when there is frost on the leaves and on the early flowers which can cause burning of the tender parts of the plant.

Over millions of years, plants have however created mechanisms to adapt to these problems. Some have thick, tough leaves to prevent rapid water loss. Our native deciduous trees have evolved to lose their leaves altogether to prevent damage to them. Herbaceous perennials die back in winter so as not to damage the tender foliage, and annuals complete their life cycle in a year so as not to face the problems the darker months create. There are also many cellular adaptations plants have made to protect their inner structures from the cold that have evolved over Some plants have turned to using the cold to their benefit – such as grasses, which need the freezing temperatures to initiate germination in their seeds.

Flower death can happen when flowers are cooled to freezing temperatures or frosted flowers thaw too quickly. This is often seen in early flowering fruit trees such as apricots and cherries. This ultimately causes irreversible damage to the flowers that then cannot be pollinated by insects, resulting in no fruit or at best a limited yield. Leaf death often happens when frosted or cold leaves are subjected to high winds, the water cannot travel quickly enough through the plant and the dehydrated leaves crisp and die. As the plant attempts to use up stored energy to recreate the leaves, stem cracking occurs causing the bark to weaken and split due to the water within the vessels of the stem of the plant constantly expanding and contracting in low temperatures.

So how can we combat the problems we often get in cold winters?

• Firstly, having a deep knowledge and understanding of our own gardens: knowing the soil type and how long it takes to cool down in early winter.
• Knowing where the prevailing wind direction is and any frost pockets can help us plan our garden carefully, so the plants are happy in their designated location.
• Choosing the right plant for each place is so important: the apricot tree we have always desired is far better suited to the sheltered south facing wall while the tough and hardy field maple can be planted further out in the open. A clever hedge planting of a hardy laurel or Holm oak can combat a north or east prevailing wind and later flowering annuals and perennials in an east-facing border will not be damaged by a bright early spring sun on frosted leaves and flowers.

For the plants we love but we know we cannot support on the coldest days, fleece can save the stems and the foliage, and bubble wrap protects roots in pots. If the pot becomes frozen, using tepid water can thaw it gently without causing further damage. A cover can even be put around the trunks of trees to help prevent stem cracking. Plants in pots can often be moved: place them in a greenhouse or conservatory to protect from the weather outside.

So how do we recognise frost damage and what do we do when it occurs?

• Wilting, browning, and dying leaves are all signs that a plant has been damaged by the cold. Tips of stems, even the wood of trees can start to turn black and discoloured. Typically, the damage is at the top of the plant and shows around the edges, as the outer branches often protect the inner ones.
• Although pruning may seem tempting, it is best left until the last risk of frost has passed so as not to damage the plant further and prevent damage to any new growth that may have emerged. Often, the plant will lose the dead vegetation naturally.
• Feeding plants at the correct time can reduce cold weather damage. As a rule, feeding plants should cease around the end of August, with a final feed of phosphorus and calcium (bone meal) to help support the plant over winter. Autumn feeding, especially of nitrogen and potassium will encourage the plant to grow new foliage which may then be damaged by any early frosts.
• Finally, ensuring that evergreen plants stay hydrated over winter is important. When pots or the ground freezes, plants cannot extract water from the soil and die due to dehydration rather than the cold itself. This is especially common in potted topiary when the containers are too small and crowded with roots.

Fingers crossed, we are now past the worst of the winter weather on the nursery and I can give my woolly hat and thermals a rest until autumn. We will still have some frosts and rain in the coming weeks and hopefully our plants (and your garden) will be ready to cope with them. Now is the ideal time to be considering your planting to ensure your plants do not get damaged in the future by our unpredictable British winter weather.