An unexpected freeze in spring or fall can quickly devastate your garden.
Early in the growing season, it is especially destructive for tender seedlings that are too fragile to survive sudden dips in temperature.
Even in autumn, when we’re trying to get as much food harvested as possible, it can force more established plants to become dormant and non-productive.
What is Frost?
Frost is defined as a thin layer of ice that forms when water vapor changes from a gas to a solid as it is exposed to temperatures below the freezing point.
Frost injures plants when water in the plant cells turn into ice crystals, which disrupts the movement of fluids and damages plant tissues.
A light frost of between 28°F to 32°F won’t wreak as much havoc on plants as a hard frost below 28°F will.
When to Expect Frost?
While keeping an eye on the weather forecast goes hand in hand with gardening, there are a few environmental conditions that will typically lead to a frost.
Cloudy nights help insulate the earth from sudden swings in temperature, but clear skies have a cooling effect that allows heat to escape into the atmosphere.
Calm conditions with little wind are more likely to reach a freezing point since very low air movement means warmer currents are not being distributed over the ground.
Clearly temperature is a major factor for frost, especially when there is moisture in the air (during foggy conditions or when dew is formed overnight) which promotes ice crystal formation.
How to Protect Your Plants from Frost
Frost may be deadly to our garden crops, but practicing a bit of vigilance and having some supplies at the ready can make a huge difference in protecting your delicate plants from the cold.
1. Bring Potted Plants Inside
When a frost is in the forecast, wait until dusk and move your potted plants and hanging baskets indoors.
Plants situated in containers are more prone to frost damage since they won’t benefit at all from the insulating powers of the earth, like in-ground plants would.
Potted plants are much more susceptible to root damage in colder temperatures.
Choose a place that isn’t too warm – as sudden changes in temperature can shock plants – such as a spot in your garage, shed, or basement.
Inspect plants thoroughly for pests and disease before bringing them inside your home. Keep plants isolated from your houseplants to prevent the potential spread of insects.
Once the risk of frost has passed, haul all your plants back outside first thing in the morning.
2. Water Plants in the Afternoon
It may seem counterintuitive but keeping the soil moist can help protect plants from the cold.
Moist soil has an insulating effect, which radiates heat upward come nightfall.
When watering plants before a cold snap, be sure to do it in the midday when temperatures are still somewhat warm.
3. Add a Thick Layer of Mulch
Just like slipping on a sweater when it’s chilly, adding a layer of mulch to your garden beds will help protect the soil from sudden swings in temperature.
Use straw, wood chips, leaf mold, or even just a heap of leaves to provide crucial insulation for the plants’ root systems below ground. Mulch heavily, to a depth between 3 to 6 inches, to create a good barrier.
Leave an inch or two opening around the central stalk so that the warmth of the soil can travel up through the plant.
Although mulching your garden beds is one of the best things you can do to keep things low maintenance, you’ll want to pull some of this protective mulch away when the weather warms up.
4. Cover Up Individual Plants with a Cloche
A cloche is a bell shaped cover made from plastic or glass that helps keep smaller plants warm and cosy in cold weather.
If you’re in a pinch, many things around the home can be used as a cloche.
When using cloches to ward against frost, place them over your plants just before nightfall and uncover them in the morning so they can benefit from the warmth and energy of the sun.
5. Give them a Blanket
To protect a larger group of plants, simply cover them up with blankets, bed sheets, towels, or drop cloths.
Before laying down the fabric, place several stakes around your plants so that when your cover them, it creates a tent-like structure.
Allow the material to drape over the plants all the way to the soil line. Don’t cinch it around the trunk or stem of the plant, as tying it off will prevent the heat of the earth from emanating up through the plant.
For extra frost resistance, add a final layer of plastic – a tarp or an old shower curtain, for instance, would work great.
Just be careful that no part of the plastic covering makes contact with your plant’s foliage as plastic can damage your plants.
Weigh down the corners and edges with heavy stones or bricks to prevent the coverings from blowing away in the night. Done just before dusk, you’ll need to remove these coverings first thing in the morning the next day.
On really chilly nights, mylar thermal blankets, with the aluminized side facing down toward the plants, helps reflect 99% of the heat back to the earth.
Place space blankets on top of plastic covers.
6. Wrap Your Trees
Younger trees, between the ages of 1 to 4 years old, are more much more sensitive frost injury, which may outright kill them.
Likewise, the buds and blossoms of fruit trees exposed to frost in spring will stunt their growth and result in a reduced harvest for the rest of the growing season.
Citrus trees are particularly frost tender and should be protected when temperatures dip to 29°F.
To protect trees from the cold, wrap their trunks with towels, blankets, cardboard, rags, or pipe insulation.
You can also use burlap or felted tree protector wraps.
Starting at the base of the trunk, wrap around and around, making sure to overlap layers by a couple inches. Keep wrapping in this manner until you reach the lowest branches of the tree.
Secure the wrap to the tree with some twine or weatherproof tape.
If temperatures reach 26°F for a prolonged period, add a layer of plastic sheeting over your wrap for added frost protection.
7. Keep the Air Moving
When frost threatens vast tracts of land in commercial agriculture, farmers have employed various tactics to simulate wind.
One such device is a selective inverted sink, a large fan in a chimney that pulls cold air up and away while it pulls warmer air down to the ground.
Another method is to task a number of low-flying helicopters to fly over crops to keep the air flowing!
While neither of these are practical solutions for the home gardener, the concept of air movement to ward off frost can be utilized at a much smaller scale.
Simulating wind this way can raise the temperatures in your garden patch by 2°F to 7°F.
On still nights with no rain in the forecast, an electric fan can be used to create an artificial breeze.
Because electronics and water don’t mix, you may wish to invest in a powerful blower made for outdoor use.
When possible, place portable fans in a sheltered spot. To ensure warmer air is drawn downward, set it up a few feet off the ground – the higher the better.
Try to situate it so that the breeze moves over every plant in the plot.
What to Do After a Frost
You’ll know your plants have been damaged by frost when the leaves and branches turn black or brown.
Wait until the weather warms up and all danger of frost has passed before pruning.
Dead branches and twigs provide a bit of protection too, so hold off until you see new growth before cutting the damaged foliage away.
How to Make a More Frost-Tolerant Garden
Save yourself the panic and heartbreak of losing your flowers, trees, and crops to a sudden frost by planning your garden accordingly.
Plants that are native to your region are much better adapted to the temperature swings of your biome.
Other frost hardy flowering plants include crocus, pansy, tulip, calendula, sweet alyssum, and snapdragon.
As for edibles, there are plenty of cold hardy veggies that often taste sweeter when touched by frost:
Root Vegetables – Carrots, potatoes, beets, parsnips, turnips, onions, garlic, radish, and rutabaga.
Cruciferous Vegetables – Broccoli, cauliflower, kale, Brussels sprouts, cabbage, bok choy, and collard greens.
Leafy Greens – Spinach, lettuce, Swiss chard, arugula, tatsoi, and mache.
When planning out your garden in the spring, avoid planting frost tender plants in low lying areas and in depressions in the ground that create frost pockets.
Since warmer air rises and cooler air sinks, plants sensitive to frost should be sowed in higher ground, in raised garden beds, or in containers that are easy to bring inside when cold weather hits.
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