Extreme Temperature Changes and Gardening

Did you ever plan a vacation to Florida and get off the plane in North Dakota? Would you want to? I once left Hawaii where it was 82F degrees (28C) and sunny and landed hours later in Montana where it was -10F (-23C) degrees and snowing. It’s an experience I don’t recommend repeating.

Late winter often provides some of us similar extremes and we don’t have to leave home to experience them. Residents along the Front Range of the Rocky Mountains are in the middle of such an event and much of the Eastern U.S. will follow soon.

A bird caught in a sudden spring storm

Yesterday we enjoyed a high temperature near 70F degrees (21C). Today will be about 45F (7C) and tomorrow we’ll be lucky to reach 30F (-1C) for a daily high. The low temperature tonight will reach 10F (-12C). Along with an 80-degree temperature difference in just over a day, we’ll also receive inches of snow.

I knew about the forecast temperature in Montana when I left Hawaii and was able to put warm clothes on in the airplane. I can do the same tonight and tomorrow for this storm. But my plants are like the vacationers to Florida. They’re prepared for sunny, warm weather and are about to be surprised by an unexpected arrival in Minot, North Dakota.

This is the time of year that can lead to damage and death of many garden plants. During the gradual climate changes of fall and early winter, plants prepare for cold conditions and change their growth cycles accordingly. In late winter and early spring as weather and soil warms, many plants come back to life and begin growing again. When a sudden burst of arctic cold interrupts that cycle they can suffer.

As a concerned and conscientious gardener it’s my job to try to reduce that suffering. By taking a few simple precautions I can limit plant damage when faced with a huge temperature swing.

It’s important to note that not all plants need protecting when conditions like these threaten. I encourage gardeners to make a regular survey of their gardens. That’s why I’m often wandering through the garden at this time of year to check on plant growth. Many sections of my yard are still buried in snow and have no new growth. Some shaded spots still have frozen ground. It’s only the areas that have started to thaw and where the plants have responded that need attention.

And even in those areas not every plant is a concern. There are perennial plants like some of my daisies and penstemons that shrug off the cold. The strawberries are peeking above the mulch but can handle freezing conditions. Many groundcovers don’t care how cold they get. A lot of plants stay partially green even through cold winters and are ready to grow rapidly when spring finally arrives. A sudden 80-degree temperature shift may slow them down but it won’t kill them. I’m not worried about those plants.

The daisies can handle cold and snow

It’s the bushes and small trees that concern me most. Buds begin to open and grow on the warm days and they’re not designed to handle extreme cold. If they grow too soon in the season and get hit by harsh cold, damaged buds affect branch, flower, and fruit growth. I’ve had an entire apricot tree lose its blossoms in an April freeze.

Frozen apricot blossoms

A tarp or blanket thrown over the plant can head off disaster. By shielding the plant and holding in some of the heat from the warm day, a simple covering can prevent serious damage. You may not be able to protect the entire bush or tree, but anything saved is good. You can’t cover larger bushes and trees and they will probably lose buds in severe temperature changes, but their size and girth should provide some natural protection.

Small and young perennial plants are most susceptible. I lost 10 lavender plants about this time last year. They were planted in early fall and made it through the winter fine. I kept them covered with protective straw through the worst months. A fellow master gardener and I checked their new growth after early-season, warm weather and confirmed they were alive, supple, and doing well. A devastating cold surge a week later changed all that.

A frozen, young lavender

Simple milk jug coverings can cover and save small plants. The protective umbrella holds some of the soil and plant heat in, usually enough to counter the sudden cold. If they’re sturdy or if you provide short supports, a tarp thrown over a grouping of plants can save them all. The concept is just to give them some protection from the cold.

Plastic protection for young growth

A close look at the forecast can save you some effort and worry. Snow is a great insulator and actually provides protection. Snow does not get much colder than 32F degrees (0C). That’s warmer than our current average night temperatures so any buds that are growing can handle 32 degrees. A blanket of snow provides a relatively constant temperature that can be well above the extreme low temperature of outside air.

So that means that if the forecast calls for inches of snow before the severe cold temperatures, a natural blanket will help the plants and less covering may be needed. If the forecast has the cold temperatures coming before the snow, that’s when you have to take protective action.

By focusing on plants you know are growing and that you know are susceptible to cold damage you can center your protective efforts. By analyzing the type of weather expected you can decide how much action is necessary.

In the end, how many of your plants survive drastic and severe temperature changes may be up to you. I’ll take another look this afternoon before temperatures plummet to make a final evaluation. My tarps and milk jugs are ready.