Protect your plants: first frost is around the corner

By Nan Fischer
For the Taos News
Posted 9/5/19

As I write this, the forecast is for another 89-degree day, the umpteenth in a row. A weak monsoon season has not brought relief each afternoon, so it seems like it will never cool …

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Protect your plants: first frost is around the corner


As I write this, the forecast is for another 89-degree day, the umpteenth in a row. A weak monsoon season has not brought relief each afternoon, so it seems like it will never cool down.

But I look at the calendar and see September is upon us. We all know the first frost comes in September. No matter how hot it's been, there is always a sudden cold front that takes us by surprise and zaps our plants. Then it moves on, leaving us with comfortable days and clean-up chores in the garden.

Despite iced drinks, air conditioning and flip-flops, are you prepared for frost?

What is frost?

Taos' average first frost date is Sept. 19. The earliest frost on record was Sept. 3, 1973, but has been known to be as late as Oct. 1.

Temperatures above 32 degrees create dew on plants. At temperatures below 32, the dew freezes, becoming frost. A light frost is considered a temperature from 29 to 32. A hard frost, or killing frost, is a temperature below 28 for three to four hours.

The extent of plant tissue damage depends on how long the temperature is below freezing. Sometimes a quick dip to 32 just before sunrise will have no lasting effect. It's not enough time for the plants to get sufficiently chilled. Tissue damage occurs when the fluid in the plant cells freezes and ruptures, so the plants need to be quite cold to exhibit frost damage.

Other factors affecting the amount of damage are the plant species, age, overall health, soil moisture and location. Some plants are more cold-hardy than others, and of course healthy plants can withstand harsher elements. As in humans, younger plants are more resilient than older ones.

Plant location speaks to Taos' microclimates. Plants on the south side of a building will naturally be warmer than those on the north side, but we have to think regionally, too. Ridges are warmer than low-lying areas, because cold air sinks and warm air rises. On the other hand, the mountains and their foothills are colder than the valley. Temperatures drop 3.5 degrees Fahrenheit for every 1,000 feet of elevation. This is valuable information when you're watching the official forecast from the airport and trying to make adjustments to your specific locale.

Get prepared

The first step in getting ready for frost is to watch the overnight temperatures once the nights start cooling off. With a high-low thermometer, you can see the lows even if you aren't up at that time. Pay attention when they consistently dip into the low 40s and high 30s. I always allow for a 5-degree margin of error, so if the forecast is for 37, I cover my plants. (My weather is similar to that at the airport.) It's better to be conservative and err on the side of caution to save your gardens! Keep a record of the highs and lows over time to learn about your yard, your own personal microclimate.

When frost threatens, bring in your house plants. Check for bugs so you're not introducing pests to the plants that stayed inside all summer.

Harvest the fruits of the heat-loving plants, such as tomatoes, peppers, zucchini and other squashes, beans and eggplant, and cut sensitive herbs, such as basil, for drying or pesto. Cut and make a bouquet of tender annual flowers, such as zinnias, marigolds and petunias. Now is also the time to dig and pot up annuals to bring inside for winter decoration.

Cool weather plants will tolerate frost. Some actually taste better afterwards! These include kale, chard, lettuce, spinach, broccoli, cabbage and peas, and root crops, such as beets, carrots, radishes, turnips and parsnips. Perennials and shrubs do not need protection, either, unless they are newly planted and have not developed strong root systems.

Water your gardens well. Hydrated plants are more likely to survive a frost, because they will take longer to cool down and freeze.

When you are done harvesting and watering, cover your plants with straw mulch, row cover, frost cloth, sheets or blankets. Use stakes to prop up cloth covers and keep them from touching the leaves. Do this at the end of the day to trap the accumulated heat. Anchor down the sides to protect from wind.

You can also turn on a sprinkler right before the temperature drops late at night or early in the morning before sunrise. This takes some attention and dedication, even if you use a timer. There is no saying when the thermometer will reach 32. This works, though, because the water that hits the plants freezes, and as it goes through this phase change from liquid to solid, it releases heat, which warms the plants. Sounds counterintuitive, doesn't it? Keep the sprinkler running until the ice melts.

If you get caught by a surprise frost, don't prune your plants right away. Wait until later in the day to assess the damage, which doesn't show up until the plants warm up in the sun. Then just prune the frozen tissue and remove fruits showing signs of frost damage. After that, adjust your watering and fertilizing to compensate for the lost plant material.

In the future

Consider growing in cold frames, a greenhouse or under low tunnels to protect from fall and spring frosts. You will also be extending the season on both ends. Covered growing is gaining in popularity, because our weather patterns are unpredictable these days. You have control over the environment, and it is more stable, which is important in a place that regularly has overnight temperatures in the 40s.

Landscaping your yard with hardy native and adaptable plants will also reduce your losses to surprise freezes.

Record-keeping is your friend. Observe the weather and your plants, and you will be well-equipped to care for them most effectively.


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