How does Frost Damage Plants?
Frost Causes the water in the plant cells to freeze which damages the cell wall and as a result the inside structure of the plant is damaged. When the ground is frozen, roots cannot take up any water to feed the plant and as a result dies.
Don’t be caught out!
Be aware, early frosts may occur From September onwards or late in spring. When an early frost occurs, not only have you not prepared your garden for cold weather and frost, the plants themselves may not have prepared themselves either and an unexpected frost can occur when they are not ready. Plants prepare themselves for the winter months by:
- Materials and chemicals – some plants store extra chemicals and materials that act as an anti-freeze lowering the freezing point of cell contents. This process usually starts when the days become shorter in autumn.
- Antifreeze – this is where the plant is able to prevent water in the cells from freezing even below freezing point. In order for this to happen, plants have to be in a cold environment for about a week or so before freezing conditions occur.
- Bark – this insulates the plant to prevent water freezing inside the plant cells
During spring there will be new growth and buds appearing, which is vulnerable and has no resistance against sudden freezing conditions.
A few things to Consider
- Golden or variegated varieties of plants are usually more vulnerable and less hardy.
- Research hardiness of plants so you don’t waste money and time planting them if they cannot withstand the cold.
- Shelter will be required for tender plants.
- Plants with flower buds and new shoots are less likely to be damaged in east-facing sites.
- Avoid if possible colder areas in your garden called ‘frost pockets’ and are usually the lowest point in your garden or near fences and garden walls.
- Newly planted and young plants will be more vulnerable to frost damage than fully established specimens as they have not developed any resistance to frosty conditions.
- Pruning and cutting back plants encourages new growth which will be damaged by cold weather and/or frost.
Protecting Your Plants
If you didn’t plan ahead in spring and consider the cold weather and frost when planting, then protecting your plants this winter may also involve a bit of re shuffling of some plants around your garden to provide extra shelter for them. Protecting your plants will also include covering them with fleece, bringing them indoors as well as adding mulch.
- Evergreen plants will need a thick layer of mulch on the surrounding soil to keep the solid from freezing so water can be taken up by the plant so they don’t dehydrate. Fleece?
- Tender Plants ideally need to be in pots over the winter so they can easily be moved indoors to protect from the frost and cold weather.
Growing in the Open: if they cannot be potted up and moved indoors, they can simply be covered in fleece. The ground around the plant should be covered in a mulch to prevent the soil freezing. In the spring new shoots can be covered with a bell-cloche until they are more established.
Potted: Move any potted tender plants indoors to protect from the cold weather.
- Plants growing against a wall can simply be protected with fleece.
- Low growing Plants will need to be protected from wet weather so a cloche is ideal to keep them covered. You can then surround them with gravel or grit to ensure they will have effective drainage.
- Tree Ferns, Cordylines and Palms will need theircrowns (centre of the plant) protecting by tying their leaves into bunches and the trunk of den trees should be wrapped in fleece.
- Tuberous Plants, once the frost has blackened the foliage, you should carefully dig them up taking care not to chop them in half with your spade. Remove the soil form the tubers and place somewhere cool and dry to allow the tubers to become fully dormant. After a few days, store the tubers in almost dry compost in a frost free place over winter such as the greenhouse.
- Plants in Pots need to be moved indoors. If you can’t move the pots indoors then you will need to use pot feet to prevent waterlogging. If you don’t have frost proof pots they may crack in the frost so you should insulate them with a layer of bubble wrap or hessian.
- Frost Pockets are the coolest places in your garden and can be found by a wall or fence and at the lowest ground levels. These areas can be damaging to plants so if possible you will need to dig up and move these plants elsewhere in your garden. If not remove some of the lower growth to improve cold air drainage.
- New plants Avoid planting any new plants as newly planted and young plants will be more vulnerable to frost damage than fully established specimens as they have not developed any resistance to frosty conditions.
- Know which ones are the Less hardy plants in your garden. They ideally need to be moved to a sheltered spot such as under a tree or next to well established shrubs if possible if they are in an exposed position. They will need to be covered in fleece and mulching may be necessary too depending on how resistant to frost they are.
- Plants with flower buds and new shoots if not already, need to be in east-facing sites.
- Do not prune and cut back plants before the winter or during, as the older foliage is vital as it will help to protect the rest of the plant and hopefully will take the hit of any frost damage. Cutting back encourages new growth which will be damaged by cold weather and/or frost.
How to detect frost damaged plants
Overall the general signs you need you look out for are withering, scorching or browning of leaves, limp stems, brown fruit.
- With hardy Evergreen plants the leaves becomes scorched and often turn brown.
- Tender Young Growth causing scorching of the leaves and pale brown patched will appear between the leaf veins, usually on the more exposed surfaces.
- Tender perennials usually become blackened and the plant stem will be limp and distorted.
- Blossom and young fruits will have a corky layer form at the flower end of the fruit
- Bedding plants and some tender vegetables will show leaf scorch and browning
- Some shrubs may have the spotting on the leaves
- The foliage of certain plants appears water-soaked and dark-green and will then turn black.
Checking for Signs of Life
After the winter, a great way of detecting frost damaged plants is to scrape the outer layer of the stem away and if it is sappy and green then it shows a sign of life. If the stem has no sap and is soft, dry and brittle this will mean that the plant may well have died. However, you cannot tell if this is the case with all plants, as climbers with woody stems don’t have green sap at this time of year, so you will not be able to tell whether they are dead or alive.
What to do if your plants are damaged
If your plant does appear damaged, so not give up hope as you never know, it may well recover. There are ways to prevent any further damage to your plants.
- Protect them from the morning sun to prevent them from thawing out to quickly. If they cannot be moved then cover them in black plastic to block out the sun.
- Cut back frosted growth in spring to prevent further die back and encourage fresh, new growth. You should be looking to cut back to an undamaged side shoot or bud.
- Feed damaged plants with a slow release plant food to encourage strong and healthy new growth. The fertiliser will need to be balanced with equal amounts of nitrogen, phosphorus and potassium.
- Dig up small tender plants and place them in the greenhouse. Provided they were not exposed to long period of cold and frost they should recover and start to produce new growth.
- Newly planted specimens if there has been a hard frost will lift up above ground level if just recently planted. Check them regularly to re-firm the ground around them and keep the roots in contact with the soil.
Remember: Many plants can actually recover from frost if you give them time, do not just give up on a plant that has been frost damaged. Even if there is no sign of life above ground, the root system may still be okay and you may start to see some growth over a few weeks. If no re-growth has appeared by mid-summer you may well need to replace the plant.
Snow actually acts as an insulator; however it can still damage plants. If there is a heavy covering, the weight of it can cause leaves, branches and stems to break. To minimise damage you will need to shake snow off the branches of large trees, shrubs and hedges. Even if the snow doesn’t break the branches it can leave them distorted. Snow on greenhouses or cold frames prevents the light from getting through so it will need to be removed. You will also need to avoid as much as you can from walking on snow covered grass as it damages the turf and will leave it looking unsightly.
Hardiness zones are useful as a guide only as there are many other factors to take into
account on how a plant may survive in your garden. For example, a damp shaded spot my kill a plant that in the same garden, would survive in a border which slopes away and has sandy soil.
How hardy is it on a scale from 1 – 11. One will survive arctic winters, eleven is tropical. The hardy zones vary across the UK from 7 to 10. Generally most of England, Scotland, wales and centre of Ireland are zone 8.
You can see the hardiness scale to the right, so before purchasing any plants check out your area first so you know how hardy your plants need to be to stand the best chance of surviving this winter.