Protecting Your Plants From Frost

In the Northeast, we are used to false-starts for Spring.

Last weekend was warm and sunny, but this weekend is shaping up to be very different; a typical story around here! If you took advantage of the warm temperatures and got to planting for the upcoming growing season, you will need to protect your new seedlings from the impending frost.

What happens when plants are exposed to frost?

In short: damage. It's tough to generalize how cold it has to be before a plant will die, so be sure to look up the cold hardiness for the plant in question before leaving the plant unprotected. Some plants can survive sub-freezing temperatures for months while others cannot take temperatures below 50° F for more than a few hours.

Light frost typically doesn’t cause major damage, with exception to very tender plants, but hard frost freezes water in plant cells, causing dehydration and damage to cell walls. Cold injury is more likely to occur as the sun comes up. As a result of these damaged cell walls, the plant defrosts too quickly, killing leaves and stems.

What can you do to minimize cold weather exposure for your plants?

According to Gardening Know How, don't panic! There are simple ways to protect your plants from freezing temperatures, including:

• Covering plants – The most popular way to guard against frost is with the use of some type of covering. Most anything will work, but old blankets, sheets, and even burlap sacks are best. When covering plants, drape them loosely and secure with stakes, rocks, or bricks. The lighter covers can simply be placed directly over the plants, but heavier covers may require some type of support, such as wire, to prevent the plants from becoming crushed under the weight. Covering tender garden plants in the evening will help retain heat and protect them from freezing. However, it is important that the covers be removed once the sun comes out the following morning; otherwise, the plants may fall victim to suffocation.
• Watering plants – Another way to protect plants is by watering them a day or two before the frost is expected. Wet soil will hold more heat than soil that is dry. However, do not saturate the plants while the temperatures are extremely low, as this will result in frost heave and ultimately injure the plants. Light watering in the evening hours, before temperatures drop, will help raise humidity levels and reduce frost damage.
• Mulching plants – Some people prefer to mulch their garden plants. This is fine for some; however, not all tender plants will tolerate heavy mulching; therefore, these may require covering instead. Popular mulching materials that can be used include straw, pine needles, bark, and loosely piled leaves. Mulch helps to lock in moisture and during cold weather, holds in heat. When using mulch, try to keep the depth at about two to three inches.
• Cold frames for plants – Some tender plants actually require over-wintering in a cold frame or indoors. Cold frames can be purchased at most garden centers or built easily at home. Wood, cinder blocks, or bricks can be used for the sides and old storm windows can be implemented as the top. For those needing a quick, temporary frame, simply incorporate the use of baled hay or straw. Stack these around your tender plants and apply an old window to the top.
• Raised beds for plants – Designing a garden with raised beds will also help guard plants against frost during cold temperatures. Cold air tends to collect in sunken areas rather than higher mounds. Raised beds also make covering of plants easier.

Is there anything you can do to revive plants that are damaged by the cold?

Yes! While not always visible until spring, frost crack results from sudden drops in nighttime temperature following the daytime heating from the sun. Unless these cracks are ragged or torn, however, they usually heal themselves. To help minimize frost damage to trees, lightly mist foliage before the sun hits them. Likewise, potted plants can be moved to another location away from direct sunlight.

Unless damaged plants are moved indoors or another sheltered area, do not attempt to prune damaged leaves or stems. This actually offers additional protection should another cold spell occur. Instead, wait until spring to cut away the damaged areas. Prune dead stems all the way back. Live stems, however, need only the damaged areas cut back, as these will eventually regrow once warm temperatures return. For soft-stemmed plants suffering from cold injury, immediate pruning may be necessary, as their stems are more prone to rotting. Cold damaged plants can be watered and given a boost of liquid fertilizer to help aid in their recovery.