A winter frost can be such a beautiful thing. White and sparkling like little diamonds. It can also be deadly for your plants.
When plants freeze, the water in the cells expand causing the cell walls to break. Since the cells of the plant carry the nutrient rich sap the plants require to live, the plant can die.
Frost can form when water vapour in cool air condenses into droplet of water that form dew on the ground and on your plants. Then, when the temperature drops below 0 °C, all this moisture freezes, creating those beautiful but deadly ice crystals.
There are three types of frost, including ground frost which covers the ground, trees and other objects that have a freezing or below temperature. This frost is also called the white frost.
Hoar frost is similar to ground frost in that it’s composed of ice crystals that formed in the same way as dew however the surface temperatures were already below freezing point. This type of frost will have a beautiful feathery appearance.
There’s also “air frost” which occurs when the temperature of the air is below the freezing point of water and at least a metre above the ground. This air frost damages plant stems, fruits and flowers and can even kill them. Occasionally you can have ground frost without having air frost If the ground freezes before the air does.
Not all plants will die all the time from frost. Some plants are much more hardy and their leaves and stems may survive. Evergreen trees and Evergreen bushes are a great example however even Evergreens and other hardy plants may be damaged or killed by extended periods of freezing, especially when the soil freezes. Frozen roots can no longer absorb water and the plant may die from thirst.
One way to tell if your plants have been damaged by frost is when the above ground parts of the plant may blacken. You can also expect to see wilting, damaged fruit, flowers and buds may become brown and drop to the ground.
By far, the most damaging frost is in the late spring. Plants with tender new growths are very susceptible to frost and quickly die.
You probably didn’t come here for a lesson on plant biology or an explanation of what causes frost. You want to gain some insight into how to protect your plants from frost. One of the first things I’d suggest is to include frost in your initial garden planning. If you live somewhere were frost may be a problem, pick hardy plants that are known to withstand the damaging effects of frost. You can ask your local garden centre which plants they would recommend for your area.
If you do choose plants that are susceptible to frost, try to plant them in against walls and shrubs or under trees to reduce wind and help protect them during the winter. If possible, do not plant your early flowering plants in the east facing section of your garden as the first warmth of the sun can quickly thaw them causing shock when the plants are unable to acclimate quickly. You can also leave old growth, leaves, etc. over your plants to help protect against frost. If you prune and cut back your plants in Autumn your new growths are more susceptible to frost. Remember that frost and cold air will descend to the lowest parts of your garden, so plan accordingly when planting tender plants.
If you have potted plants which you kept inside during the winter, take your time putting them back outside. Make sure there’s no chance of a surprise frost which could quickly kill them.
You can also use horticultural fleece [Amazon] [eBay] to protect your plants. To be doubly sure you can put a layer of straw, plant material or old leaves between two layers of the fleece to provide the best insulation against frost.
If you need to immediately protect your plants from frost, use an upturned bucket, bin or box to cover the plants. This is a quick protection however you must remember to uncover your plants later in the day so they get sunlight.
Some plants with flowering bulbs and perennials that die back can be covered with leaves, manure mulch or straw to prevent the soil from freezing. Make sure you remove the mulch in the spring or it may act as an insulator, trapping the coldness in the soil.
Even though Evergreens are hardy, you can protect them from ground frost with a thick layer of mulch. This will help prevent the roots from freezing under the soil which could cause the plant to become dehydrated.
Cordylines, palms, small trees and ferns can be protected by wrapping the crowns and trunks layers of fleece stuffed with straw.
When using outdoor pots in the winter, make sure they are frost proof. Also, place pots on sticks or feet to prevent them from becoming waterlogged when the bottoms freeze to the ground. You can insulate the inside of your pots with a layer of hessian or even bubble wrap.
Here’s an interesting article by Andy McIndoeh about frost proof pots. www.learningwithexperts.com/gardening/blog/is-this-pot-frost-proof
My plants have frost damage, are they going to die? Now what do I do?
Even if your plants have been damaged by frost, they may survive and you can greatly assist them by minimising the frost damage.
In the spring cut back any damaged growth on your plants to encourage new growth. If your frost damaged plants are small enough, dig them up and bring them into your greenhouse. They may recover quickly.
According to the Doubleday Research Association; Giving your frost damaged plants liquid feed, such as Comfrey tea, will encourage new growth.
We would love to hear about your experiences with frost. Let us know if you have any good tips to share with our readers. Good luck!