Margaret Lauterbach

This winter has been unusually warm. Here are garden tips if we get another freeze.

Tulips are starting to come up in this office garden off Ustick Road last week.
Tulips are starting to come up in this office garden off Ustick Road last week. Statesman photo

We’ve had some beautiful weather this winter, making up for last winter’s long-lasting snow blanket and choking inversions.

But it’s created some challenges for gardeners, such as early growth — right now, snowdrops and winter aconite are in bloom in my shade garden, and hellebores and trilliums are poking their heads above the surface too.

I confess I’ve been starting alliums and brassicas in the greenhouse, as well as some peppers. It may be too early, but it certainly brightens my mood. If you planted lettuce seeds Thanksgiving, as many do, you might be seeing tiny seedlings ready to grow up. Some old-timers will tell you not to store the longjohns just yet, for we’ll have more cold weather before spring arrives. It doesn’t look like that’s coming, though, with long-range forecasts seeing relatively mild temperatures.

If you fertilized your lawn in November and/or December, it’s greening up now. In past years we’ve had to mow in April; this year, we might be starting in March.

Budding trees

What about the rest of the yard?

If you have non-fruit trees already budding out, don’t worry — a freeze will not prevent their leafing out.

Many trees will flower, and if those flowering buds are destroyed, that will just mean fewer seeds will drop and folks who usually suffer from spring allergies will breathe easier. Some trees afflicted with disease drop their leaves and refoliate a few times during the growing season.

Fruit trees are another matter. In Idaho, a lot of the state’s revenue and agricultural product is tied to fruit production.

If trees begin to bud and show color and then we have a frost or freeze, what happens? The low temperature will affect fruit tree buds, depending on how low the temperature drops, for how long and how far advanced the bud blossoms are. For instance, 10 percent of apple blossoms in “full pink” will be killed by temperatures of 28 degrees F., if that temperature lasts 30 minutes. But 90 percent of them will be killed by a temperature of 25 degrees F. If the buds are still green instead of blooming, 90 percent of the buds will survive temperatures down to 23 degrees F. for that period of time.

If you’ve grown apples, you may have noticed that the blossoms occur in clusters, one blossom larger than the others, and the blossoms opening at different times. Orchardists call this large blossom the “king” blossom. Since all of the blossoms do not open on the same day, those later-opening blossoms may become the apple-producing survivors of the season.

Different fruit buds tolerate different cold temperatures, too, according to compilations gathered by extension specialists at Washington State University and Michigan State University. In full bloom, 90 percent of blossoms of apricots, peaches and plums survive a half hour of 27 degrees F., while sweet and tart cherries are slightly hardier, surviving 28 degrees F. If buds are just beginning to swell, they’ll survive much colder temperatures, into the teens.

What can you do for your fruit tree if frost is in the forecast?

We used to be able to hang Christmas lights in fruit trees to keep buds, flowers or tiny fruits warm, but those modern lights have no heat. If the forecast frost is to be a light one, accompanied by wind or breezes, that is the best scenario. You could set up a fan to move the air in your fruit tree or spray it with water to freeze around the buds. As the water thaws in warming sunshine, the thawing effect of water raises the temperature a little. Or you could try covering the tree, although if the tree is large, that’s a difficult operation. If you can cover and install at least a regular light bulb under the cover, it could warm enough of the tree to preserve at least part of a harvest. YouTube has plenty of options for preventing freeze damage.

Gauging temperatures

One thing to keep in mind is that temperature forecasts and reports occurs at a gauge about 5 feet above the surface of the soil. Since cold falls, the temperature at ground level will be colder than forecast or reported. One study showed a 6-degree drop from thermometer to soil surface. Most of the temperatures forecast or reported are for a certain length of time, too. A shaft of cold air “kissing” squash plants in my garden killed leaves last year, although the reported temperature was 38 degrees F.

As far as bulbs are concerned, they’re encased in natural antifreeze, and will not suffer in freezes. If your daffodils are in bloom, a temperature of 15 degrees F. will cause flowers to droop, and they’ll never overcome that. Pick them for use in a vase before that cold temperature. But don’t mix them with other flowers — daffodils are in the narcissus family and so exude a sap that clog the stems of other flowers.

Other tips

▪  Roses should be OK, but don’t start pruning them until forsythia blooms. If you’re eager for spring, cut some forsythia twigs and put them in a vase of warm, almost hot, water. Change the water each day, and they’ll bloom indoors earlier than outdoors.

▪  Don’t forget to prune your grapevines this month. If you wait, they’ll bleed sap and, although it’s not a fatal problem, it’s messy.

▪  Planting onion seeds, sets or seedlings now is a gamble, because if the weather turns cold then warm again, they may go to flower and seed, ruining the bulb for culinary use. Other biennial plants may also go to seed in similar conditions.

▪  We’ll have enough water for this coming year, according to hydrologists at the Natural Resources Conservation Service, because we have an abundance of stored water in reservoirs even though the current snowpack in the mountains is less than normal. Researchers will continue measuring until April, and late February and March usually see more abundant precipitation.

Of course frost tender crops such as corn, tomatoes, peppers, beans, cucumbers, melons, squash and eggplant should not be sowed until the soil temperature is 60 degrees F.

When starting seeds indoors, we usually try to heat the planting soil for all seeds, but not all seeds germinate in high temperatures. Seeds for many crops such as lettuce, parsnips and spinach won’t germinate if the temperature is too high. I have my heat mat set to 80 degrees for peppers and eggplant that I’m germinating now, but must wait until later to re-heat it for tomatoes, basil and tomatillos. They shouldn’t be started until close to transplant time. Setting them out in mid-May to June 1 usually works best.

Most brassicas or cole crops such as broccoli, cabbage, Brussels sprouts, collars, kale, and kohlrabi shrug off frosty weather, so they may be transplanted into the garden at this time. If we have a hard freeze forecast, a floating cover usually protect the plants. These are all easily germinated indoors at room temperature.

Send garden questions to or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

Worried about the mild weather?

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