Betsy Lyman is a gardener and freelance writer.

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Oh No! It’s Going to Freeze Tonight!
by Betsy Lyman    

When late spring temperatures drop below freezing, it’s time for your plants to take cover.

Few things strike terror in the heart of a gardener more than a forecast for a late spring freeze. And let’s face it, with this year’s rollercoaster ride of temperatures it is hard to know what’s around the corner. But I think you’d agree that if this year’s wacky weather patterns continue, chances are good that a late spring frost could be in your garden’s future. To avoid being caught off guard, here are some tips to help you prepare.

Get Ready ‘Cause Here it Comes

The best time to get ready for an overnight freeze is weeks before it happens (like now). Why? If you’re like me, you have been guilty of doing the old last minute frost scramble. Trouble is that if you wait until the day before the frost to prepare it is often difficult to find all the coverings you need. By gathering up the materials ahead of time and storing them all together, when the time comes to cover your plants all you’ll need to do is grab and go.

What’s in and What’s Out  

The first step in preparing for a spring frost is to figure out which plants you’ll need to cover. While every year is different, if you’ve gardened in the same spot for a few years, you may be familiar with your garden’s sequence of spring-blooming plants. Garden journals from previous years and photos with date stamps can be helpful reminders. But even if this is your first garden, there are plants that often need spring frost protection such as young vegetable and flower seedlings, flowering fruit trees and shrubs, spring-blooming bulbs and containers of mixed season plants.

Crocuses are cold-hardy plants that don’t require frost protection. They are among the first flowers to bloom in spring so they often experience freezing temperatures.

However, not all flower and garden plants have to be covered. There are several kinds of cold-tolerant plants that can survive brief bouts of mid-20 F temperatures. A few examples are crocuses, tulips, narcissus, grape hyacinths, pansies, nemesia, diascia, snapdragons and osteospermum as well as collards, cabbage, spinach, kale, peas, radish and leeks. If you are in doubt about a plant’s ability to withstand temperatures below 32 F, call your county extension service or check reference books or online sources.

Once you’ve identified the plants that need to be covered, the next step is to determine the size each covering should be so that it can adequately protect your plant. Sometimes the height and width of a tree, shrub or a planting bed is hard to judge in an outdoor setting, so a tape measure is helpful to get the correct measurements.

Size Matters

Why measure your plants? To be effective, a cover needs to be large enough to drape over the plant on all sides to trap warm air rising from the ground and to prevent the outside cold air from getting to the plant. Anything that creates a dead air space between the ground and the plant will do the trick. For trees, shrubs or large plants you may need to sew or pin together several old bed sheets, while for small seedlings a plastic container will work. Almost any type of covering from cloth to cardboard boxes to plastic milk jugs will do.

Avoid any covering that is too heavy or too small so that it crushes or breaks your plant’s stems. Some gardeners have saved plants from freezing only to lose them from being crushed under heavy covers.

A bonnet of wire fencing held aloft with a wooden stake creates a framework for plastic sheeting over a raised vegetable garden bed. The sheeting will cover all sides of the bed to create a protective shield for the plants from freezing temperatures.

Just remember that if you use sheets of plastic, they need to be elevated above and around the plants. Why? If frost forms on the outside of the plastic it transfers that cold to any place it touches the plant. There are several ways to create a framework around your plants to hold the sheeting. Some gardeners use pieces of lawn furniture such as chairs, tables or a chaise lounge. Others create a bonnet effect over the plants with hoops of wire fencing. Plastic plumbing pipe, wooden stakes, tomato cages, overturned carts and wheelbarrows can also work. Plastic is often preferred for protecting plants during a windy night, so if those are the conditions you face, double up and cover the framework with plastic along with a blanket to increase the amount of insulation.

Now, with your list of plants and the sizes of covers that you will need, you can gather the right types of materials. You might already have many of these items on hand or you can get them from friends and neighbors or pick up at yard sales. By preparing early you’ll have time to modify the coverings or sew them together to make large wraps. You’ll also have time to save the right size and number of plastic containers you’ll need. If you use milk or soda bottles as coverings, cut off the bottoms of the containers but save the screw-on tops to make them air tight over the plants.

Here are a few frost covering options:

Soft and Lightweight Fabrics
Old sheets, tablecloths, lightweight blankets, bedspreads, curtains, pillowcases, towels, commercial row covers and plant fabric covers

Vinyl or Plastic Material
Tarps, clear plastic sheets, commercial plant covers, garbage bags, buckets, liquid containers (milk, soda and water), food containers (cottage cheese, deli and yogurt), flower and nursery containers (be sure to cover the holes on the bottoms of the overturned plastic pots)

Cardboard boxes (can be collapsed and stored), newspapers, garbage cans, large glass jars, terra-cotta pots

Make it Easy on Yourself

Storing all your plant protection supplies together will save you time when a spring frost is looming. A rolling garbage can makes it easy to transport your materials around the yard and garden.

A great way to store your frost protection materials is to stash them in one or more rolling garbage cans. Keep the cans tucked away in the back corner of your garage or basement. That way you won’t be tempted to use your designated frost coverings for other projects. Remember, we want to avoid the frantic frost scramble! When the time comes that you need them, just roll the cans around the yard to transport the covers to the plants. The rolling containers also make it easier to pick up the coverings the next day.

A Few More Tips

With your materials stored away, you can relax knowing that if a frost is predicted, you’ll be ready. As you watch your local weather forecast, remember that a TV station’s predicted low temperatures are often based on where they are located, not in your garden, so adjust accordingly. There are online weather sites that let you put in your address and find a weather reporting station closer to home. However, anytime a forecast for your region is going to be near 32 F, it is time to spring into action.

Shelter your plants before the sun sets so you can capture as much warmth from the soil as possible. And remember that cold air is more dense than warm air, so it sinks to the lowest point. Low-lying areas of the garden can be several degrees colder than other areas. Consequently, frost may occur in these areas when there is no frost evident anywhere else in the garden.

Water Then Cover

As odd as it may sound, an important line of defense in protecting your plants from frost is to water the soil around them. Studies have shown that moist soil holds much more heat than dry soil so you can enhance the soil’s ability to capture warmth during the day and deliver it to your plant during a cold snap by making sure it has consistent moisture. However, watering alone will not provide all the needed protection from a freeze, but watering combined with covering your plants can make the difference between a plant’s survival or its demise.

Turn up the Heat

Adding other sources of heat under your frost coverings may also help protect special plants. Fill plastic jugs with water and then leave them in the sun to absorb the warmth. When they are placed next to the plant under the wraps, the water will release its heat through the night.

Watch Out for Wind

Few things are more frustrating than to go to all the work of covering your plants only to have the wind or even a light breeze blow them off during the night. To keep that from happening, secure your coverings to the ground. Gardeners often use stakes, U-shaped wire pins, boards, bricks, rocks or soil.

Wait for the Light

The next morning, don't remove the frost covers if it is still dark; preferably, don’t remove them until late in the morning. Some of the coldest temperatures are just after sunrise. The timing of removing the covers might not coincide with your work schedule, but be aware that taking the coverings off too soon may make the plants vulnerable to frost, or leaving them on too long could cause the plants to overheat. And if the weather calls for more than one night of frost, don’t leave the plants covered during the day unless daytime temperatures remain below freezing.

Photos courtesy of Betsy Lyman.


Posted: 03/10/14   RSS | Print


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