When we talk about cold shock, it is usually after an unexpected cold spell that affected our outdoor plants like tender miniature roses, perennials and flowering shrubs. But cold shock can occur indoors as well. Perhaps a houseplant is located too close to the main entrance of your home where the cold outdoor air hits it every time someone enters or leaves.
A tropical plant can suffer cold shock when temperatures drop below 50 degrees. Perhaps you have a plant that needs full sun and you have placed it on a windowsill to give it the best sunny spot. The window could allow cold outdoor air to infiltrate into the home — and if the glass isn’t insulated, damage to your plant can occur to any foliage that is in contact with the glass.
What Is Cold Shock?
When plants are exposed to temperatures below what their native grow zone is, they will be vulnerable to cold shock. That is why every plant is identified with a hardiness rating that matches where it can safely be grown. Most houseplants are tropical plants that can safely grow in a heated home during the winter. They will never survive outdoors in winter unless you live where the temperature stays at least above 50 degrees.
In northern zones 4 and 5, plants need to survive months of below freezing weather every winter. Most of these plants will go dormant in the winter. They drop their leaves, and the bare branches look almost dead until spring when new buds form and the plants look perfect. But even these plants will be at risk when the temperature drops to below zero for unexpected extended periods of time.
When temperatures drop to below freezing, the water inside the leaves freeze. On a cellular level, this means that as the water turns to ice, it expands, rupturing the cell wall. This is permanent damage, but it doesn’t mean the plant will die. If the damage is isolated to a portion of the plant, it can be revived and recover. The focus is on minimizing the damage.
What Are the 4 Signs of Cold Shock?
While some of these signs can be obvious, others can be much more subtle. There are four signs of cold shock, including:
- Leaves Wilt or Droop — As the cell damage occurs, the leaves will lose their rigidity and start to droop or even curl in on themselves. If you have been watering as usual, it is time to consider other causes for your plants’ wilting and drooping appearance including cold shock.
- Leaves Become Discolored — As the leaves die, there may be white or yellow spots on the leaves. On some plants, the leaves will turn red. Sometimes, the entire leaf changes color while other leaves may only have spots of damage. The total actual damage may not be apparent immediately.
- The Foliage or Even the Entire Plant Becomes Mushy and Turns Black — This is almost certainly an unsalvageable plant.
- The Root Ball Becomes Loose — This is an indication that the roots of the plant have also frozen and been damaged. Damage to the roots is also a sign that this plant is in dire shape and most likely will not survive.
How Can You Treat Cold Shock?
All your efforts now will be directed toward minimizing the damage. The first thing to do is check the weather forecast. Was this cold snap a one-night stand or is it possible that nighttime temperatures will continue to drop for several days? If it was a one-night occurrence, all your efforts will be toward recovery. However, if this cold snap is going to continue, your efforts will need to prioritize preventing further damage, including
- Water the Plant — The first thing to do is to water your affected plants. An inch of water will help your plant to recover.
- Avoid Fertilizing — Do not fertilize your plants during this time. Fertilizing can stimulate new growth, which will further stress a plant that is trying to heal. Also, any tender new growth will be very susceptible to cold damage.
- Avoid Pruning — You may be tempted to prune away the damaged areas but have patience. Leave your plant to recover until the weather warms and the new buds will tell you where the dead tissue starts and ends. Heavy pruning of a plant in cold shock can further stress the plant and could encourage new growth when the plant needs all its energy to be directed toward recovery. The exception to this is a soft tissue plant that has areas of black or mushy stems or leaves. This is rot and will spread to healthy areas if left on the plant.
- Bring Pots Indoors — If your affected plants are in pots, you may think that bringing them into the house is the best thing for them. However, the extreme temperature change from the cold outdoors to the warm indoors can also stress your plants. Move them into the unheated garage first. This will protect them from further cold damage and give them the time to acclimatize to the warmer temperatures. After a few days, bring them into a cool room in your home.
- Group and Shelter — If you can’t bring the potted perennial plants indoors, group them together in a sheltered area if possible. This grouping will help the plants to insulate each other from the cold. Grouping them together will also make it easier for you to add extra plant protection from the cold temperatures.
- Trim Dead Roots and Repot — A root ball that is now loose in its pot can be a grim sign of severe damage. You can attempt to save the plant by removing it from the pot and trimming any obvious dead roots away. Then, repot your plant in fresh potting soil and water gently. If there is enough of the root system undamaged, your plant may survive.
- Use the Sun from a Windowsill — Indoor plants, as mentioned earlier, can also suffer cold shock. If you have placed your brightly blooming amaryllis bulbs or houseplants on the windowsill to give them the most sunlight possible, the cold from outside might be the culprit. Put your hand on the window to see how cold it is. If the leaves are in contact with the glass, that could be the cause. If the window doesn’t seal properly, the cold air could be causing a draft that is affecting your plants. Move the plants back from the window where they still have the benefit of the sunlight but aren’t exposed to the cold glass or drafts.
How to Prevent Cold Shock
While it is possible for plants to survive cold shock, the best treatment is prevention. In the last few years, we gardeners have had to manage all sorts of unusual weather patterns, from drought to flooding and from unusually high temperatures to unusually cold temperatures.
Every part of the country has been affected in one way or another. It can be difficult to determine what each season may bring so preparation is key. There are several tips to manage cold shock, including:
Choose Your Plants Carefully
Whether the plants are for outdoors or indoors, the choices you make will determine how much care the plant will need and how vulnerable it will be. Always check the hardiness rating for your plants. Try to limit yourself to plants rated for your grow zone or even a zone colder. This will give your plants the best chance of making it through an unexpected cold spell.
Let native plants be the backbone of your gardens. We have so many plants available to us today as the plant hybridizers are always working to expand the hardiness of plants to make them available to more gardeners. It's a thrill to include hybridized plants that were not possible to grow in your zone before!
Just remember that they may need a little extra attention, especially the first couple of seasons when preparing your landscape for winter. If you do decide to risk growing a plant for a warmer growing zone than yours, grow it in a pot so that it can be given added protection or even brought indoors if necessary.
Shop Sweet-Scented Miniature Roses Provide Your Plants Shelter
If you are planting a more tender plant in your landscape, choose a location for it that is more sheltered. Protect it from the prevailing winter winds which can cause a great deal of damage. Try to plant it where you can use the house or a hedge as a wind barrier.
You can make a barrier from wind and cold by using stakes and burlap to surround the shrub. While this will help protect the plant from wind, burlap is not as effective against the cold. If the plant is small, you can invert a bucket over the plant. Remove the bucket when the sun comes up and the temperature returns back above freezing.
How to Protect Your Garden Plants
One of the most difficult times is when frost is predicted in the spring when the fruit trees and shrubs are already flowering, and you have plants in the vegetable garden. In the garden, you can divide your plants into three groups.
- Night Frost Survivors — You likely will have plants that should be able to survive a night of frost. These include brassicas (cabbage, broccoli, cauliflower), peas and spinach. These should be okay, but it won’t hurt to cover with a bed sheet or a frost cloth.
- Protection Required — There are other plants that probably can tolerate a fair amount of cold, but protection would be better. This includes plants like peppers and some herbs.
- Cold Intolerant — Then, there are plants that can’t tolerate any severe cold. Tomatoes will never survive the frost. If you have already planted your tomato plants in the garden, the safest thing to do is dig them up and move them to the garage or basement until the cold spell is over. Once the danger is past, you can replant the tomatoes in the garden. They may suffer some transplant shock, but they will be alive.
Shop All Living Plant Gifts from Jackson & Perkins How to Protect Your Orchard from Cold Frost
If you have a small home orchard that is already blooming, there are several options to try to save this year’s crop. The size of the trees will help determine which method is the best to try, including:
- Wall of Water Method — You can try the wall of water method which is used by many large orchards. In this method, the tree is completely covered with water which will freeze and envelop the tree in a wall of ice. There are also other wall of water products you can purchase. The theory is that the energy is used to freeze the water instead of the tree. The tree needs to be covered with water, so a good sprinkler is the best method. The ice will melt when the sun comes up and the temperature rises.
- Burn Barrel or Patio Heater — If your trees are planted in a block, you can place a burn barrel filled with wood in the center of the block. The fire will keep the temperature warmer, and when the fire dies out, the metal of the barrel will continue to give off radiant heat. If burning isn’t allowed in your area, a patio heater can help. The negatives of the patio heater are cost and wind. These heaters are usually fueled with propane so it can be quite expensive to heat through the night. Secondly, if it is windy, the heater will be ineffective.
- Bed Sheet Covering — If your trees are small enough, you could use a bed sheet to cover the branches and cinch the sheet around the trunk to keep the cold air out. It is estimated that a bed sheet will keep the temperature about three degrees higher.
If you know a cold night is coming, the best you can do is to prioritize what you most want to save. Use as many techniques as you can to get your plants through. It is heartbreaking for a gardener to lose a plant to one freak night of cold. Hopefully, some of these suggestions will prevent that from happening.
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