A gardener’s utmost reward is reaping a bountiful harvest after a summer’s hard work. But here comes a showstopper–unexpected frost that is set to leave devastating damage before picking your juicy tomatoes. Want to know how to protect plants from frost? Continue scrolling down to learn more about how to protect plants from freezing.
What is Frost? Key Temperature Definitions
Frost is a weather phenomenon when water molecules form ice crystals on or inside the plant surface. As plants constitute roughly 95% water, the frosted water in the crop tissue arrests its functioning and kills it later. Ice crystals build up when the ground surface temperature plummets to 32 °F (0˚C) or below; or when the air temperature is above freezing between 33-36 °F (1-3 °C), depending on other physical factors. Hence, if this was forecasted 1-2 days earlier, you will need to start covering your plants to prevent frost.
With the advancement of technology, frost damage can be completely avoided or minimized—allowing anyone to enjoy the last-season produce of your tomato plants. The National Weather Service is the responsible body for helping gardeners in the decision-making process to avoid frost, using the following terms:
- Frost advisory — is issued when the air temperature is predicted to plunge between 33-36 °F (1-3 °C) with a relatively calm wind velocity of less than 5m/ph (8 km/h). The formation of thin ice crystals is likely, even with a slightly higher temperature, as radiation freeze can occur. It happens when the heat from the ground rises, and the cool air above is pushed—the result is freezing temperatures.
- Freeze warning — refers to the likelihood of considerable and widespread freezing, with temperature forecast at 32 °F (0 °C) or below. Strong wind gusts above 5m/ph (8 km/h) can cause advective freezes. It brings icy cold temperatures that can actively frost plant leaves.
- Moderate freeze — This warning is a widely destructive cold snap for plants, with night temperatures between 25-28 °F (-4 to -2 °C).
- Severe freeze — Temperatures are predicted to drop below 25 °F (-4 °C), which can leave a significant blow to crops.
How Frost or Freeze Hurt and Affect our Plants
The surface frost is not entirely damaging to plants. The freezing temperatures can induce the clumping of water molecules at the cellular level, forming sharp-edged frost crystals that can perforate the cell walls. The leakage of the fluid dehydrates and deactivates the normal functioning of the cells, leaving massive damage to the plant tissue that is irreparable.
Signs of Frost Damage
Before delving into the approaches to protect plants from freeze damage, here are the signs that are expected after frost damage:
- The water-soaked appearance of the leaves
- Leaves are darker than usual color as a result of cell content leakage
- Blackened distorted limp growth is proof of past frost damage
- Watery or mushy fruits
How to Protect Plants from Frost – Key Methods
Frost protection for plants may include one or more techniques to minimize the damage to an outdoor garden. The following summarizes best way to protect plants from frost:
- Fetch your plant outdoors — This method works for lightweight and small plants, including potted tomatoes, herbs, hanging plants, and tender ornamentals, which can easily be transported indoors where it is warm and cozy. Wait until sunset on the night of the forecast.
- Blanket garden beds with mulch — If your vegetable patches are grown in raised beds, putting soil mulch can help trap heat and insulate the soil. Layer approximately 3-6 in (7-15 cm) of organic ground covers, such as grass straw, wood chips, sawdust, or a heap of dried leaves.
- Water the soil — While one might think this can freeze the ground, watered soil retains heat more than dry soil. This method would only work in light frost or if done on a sunny afternoon before the cold spell. Water moderately, as usual, to not oversaturate soil because it can also freeze with sustained subfreezing temperatures.
- Cover with fleece, cloth, or plastic — Plants grouped in a raised bed outside become cold-proof with old fleece, cloth, or multiple layers of plastic–the most economical and feasible way to protect plants. Use old bed sheets or similar insulating fabric to cover the entire patch: the more layers, the better the heat-trapping effect.
- Wrap potted plants' containers — potted plants are more predisposed to cold temperatures as snow than ground-planted ones. Hence, one preventive measure is to wrap the pot, including the soil, with plastic bubble wrap.
- Envelope susceptible branches with burlap — Young trees or tropical trees have less tolerance against frost. To not kill your fragile sapling from cold, wrap the stems with burlap nets or felted tree protector wraps.
- Place tender plants in a protected site — preferably on the leeward side or the direction opposite from the wind, to eliminate icy wind burn. Will a covered porch protect plants from frost? Yes, it will provide partial protection from light ice and chilly winds.
- Uproot tender perennials — Tender perennials are plants that cannot withstand deep freeze (roots, bulbs, tubers, and corms). If the air temp is forecasted to plummet, take them out from the soil and store them in a frost-free zone such as in the garage, potting sheds, or greenhouse.
- _Move your plants in an improvised mini-greenhous_e — If you don't have a greenhouse, you can still DIY a freeze-absent zone with a cloche or cold frame. A cloche is a bell-shaped glass used to cover the entire bush. To make it, cut the bottom of empty milk or water bottles, and shelter the whole plant canopy. Big pots can also be turned upside-down to have the same effects.
- Overhead irrigation/sprinklers — This works by sprinkling your plant when temperatures are expected just below freezing. The idea is that those water droplets, finer than rain, form ice sheets on the delicate flower buds and protect them from minus degrees of cold. Michigan State University extension greatly explains this in their article for preventing spring frost damage.
How to Cover Plants from Freezing
Protecting plants from freezing should be easier than mounting a tent. Learn how to cover plants from freezing with the following easy steps:
- Install supporting arches or poles that are taller than the plants enough to room the bush.
- Put on the cover of your choice. Ensure that the entire patch is covered, having no holes or any possible entrance for the cold. Refrain from making the leaves come in contact with the cover when using plastic.
- Add another layer of plastic for added protection if severe frost is forecasted.
- Place heavy stones or bricks to prevent the insulating barriers from being dragged with wind gusts.
- Remove the improvised insulations once the next day when the temperature rises above 39-41 °F (4-5 °C).
- For smaller plants and small gardens, use DIY bell chambers like plastic bottles.
What to Cover Plants with in Cold Weather
The cold weather may be unstoppable, but nothing can beat a prepared gardener by covering plants for frost. If you have asked the question, What do you cover plants with in cold weather–the following should help you:
- Industrial plastics such as polyethylene, bubble wraps
- Old bedsheets, towels, blankets, fleece, duvet, drop cloth
- Organic materials like burlap nets, felted tree protector nets
- Grass straw, sawdust, wood chips, or dry leaves for covering the soil.
- Large unused pots
- DIY covers like empty water or milk bottles
How to Manage with Frosted Plants
Plant frost protection is the best method to minimize the damage caused by icy environments. However, some crops would inevitably be susceptible despite all the measures taken. Delicate leaves and herbaceous stems turn black or brown and sometimes appear water soaked when the tissue has been penetrated by the cold. The inflicted injury cannot be cured at this point, especially for tender annuals and perennials. What can be done is to wait until the frost has gone and prune the damaged parts. They still proved a blanketing effect if another frost occurred.
Which Plants Need Protection from Frost
Various garden’s favorite plants naturally succumb to unbearable freezing temperatures, such as delicate flowers and foliage ornaments. Below is a list of which plants need protection from frost:
- Warm weather vegetables — Summer crops like tomatoes, beans, peppers, eggplant, melons, squash, okra, and cucumbers are usually intolerant to cold.
- Tender herbs — A few temperate and tropical herbs, including basil, lemon verbena, stevia, lemongrass, calendula, borage, dill, and cilantro, needs lavish pampering from frost.
- Tender ornamentals — Bougainvillea, some cacti, cape honeysuckle, coral vine, fairy dusters, ficus, hibiscus, lantana, natal plum, pygmy date palms, succulents, and other tropical plants should be protected from the cold spell.
Frost Hardy Plants
Some plants are blessed with a natural anti-frost mechanism or are bred to tolerate frigid environments. You can exempt these plants from your garden frost protection program:
- Root vegetables — plants with a carbon-dense storage organ that allow them to handle the cold spell, including carrots, potatoes, sugarbeets, beetroots, parsnips, turnips, onions, garlic, radish, and rutabaga.
- Cabbage family — crucifers or plants that belong to the cabbage family tolerate frost, including broccoli, cauliflower, kohlrabi, kale, Brussels sprouts, cabbage, bok choy, and collard greens.
- Salad greens — Many varieties of spinach, lettuce, Swiss chard, arugula, tatsoi, and mache can withstand up two a few degrees of negative temperatures.
- Herbs - Some cold-hardy herbs like rosemary, thyme, bay, chives, oregano, and mint can resist sudden temperature drops
- Hardy perennials — can withstand mild frosts such as hostas, Siberian iris, sedum, peony, and coral bells.
FAQ
Best Way to Protect Plants from Frost?
Protect your plants from frost by covering them with multiple layers of plastic or bed sheets; putting them in mini-greenhouses like an improvised plastic bottle cloche also barriers cold air from damaging frost-sensitive crops.
What Temperature Should I Cover My Plants for Frost?
Start covering your plants when there is a frost advisory, usually when the air temperature is expected to plummet between 33-36 °F (1-3˚C). Surface ground temperature can reach freezing point even with slightly higher air temperature.
At What Temperature Should You Cover Your Plants at Night?
Cover your plants if 36˚F (3 °C) is predicted to occur at night. While the air temperature is above freezing, the temperature inversion between the ground and the air causes the earth to reach icy cold temps (radiation freeze).
How Long Can You Leave Plants Covered?
You can cover your plant overnight after the expected cold snap has passed. However, if a series of frosts occur, it would be best to protect it for several nights to prevent further damage.
Will a Covered Porch Protect Plants from Frost?
A covered porch provides partial protection from frost if it faces the leeward direction of the house or if the cold spell is expected to be mild. Most often, the wind exacerbates the effect of air temperatures alone.
