Nearest Climate Station Altitude Last Spring Frost First Fall Frost Growing Season
MASON CITY, IA 1105' May 6 Sep 27 143 days
Last and first frost dates are 30% probability. Calculated using 1981-2010 Climate Normals.
HOW TO PREDICT A FROST
PREPARING AND PROTECTING YOUR GARDEN FROM FROST By Catherine Boeckmann
Frost is one of a gardener’s worst foes! Learn how to predict frost, differentiate between a light frost and a hard freeze, and protect your garden from frost with these tips!
KNOW YOUR FROST DATES
Know your average frost dates. Put your zip code in our Frost Dates Calculator to find frost dates for spring and fall in your area. Warning: These are averages so it’s what is typical. Every year will be different.
Also, the frost dates are based on a 30% probability, meaning that there is a 30% chance of a frost occurring after the given spring frost date or before the fall frost date. (In other words, these dates are NOT absolutes and should only be used as rough guidelines!)
Know Your Microclimates
Keep in mind that the occurrence of frost can vary greatly by microclimate, too. In fact, while you may have frost in your garden, your neighbor across the street may see no sign of it!
A microclimate is exactly what it sounds like: a climate on a small scale. For example, if your garden is located at the bottom of a hill where cold air settles, it’s likely to be impacted by frost earlier than a garden at the top of the hill. Or, if your plants are abutting a rock wall in full sun, they’ll be kept warmer to some extent by the heat given off by the rocks.
5 TIPS FOR PREDICTING FROST
Consider these factors when the radio and TV reports say “frost tonight”:
Temperature: How warm was it during the day? It may sound simple, but one of the best ways of determining of a frost is due overnight is to gauge the temperature. If the temperature reached 75ºF (in the East or North) or 80ºF (in the desert Southwest), the chance of the mercury falling below 32ºF at night is slim. See our 7-day forecasts to check your weather forecast.
Is it windy? A windy night is also likely to reduce the likelihood of a frost. A still night allows cold air to pool near the ground; a light breeze stirs things up; a heavy, cold wind sweeps away warm air near the ground.
Is it cloudy? Observe the sky. If the Sun sets through a layer of thickening clouds, the clouds will slow radiational cooling and help stave off a frost. With clouds, the risk of frost is reduced.
Slope: How is your garden landscaped? Gardens on slopes or high ground often survive. However, cold air sinks and will puddle down into the valleys and hollows. If your home and garden are at the bottom of a slope or in a valley, and there is no wind, then there is higher risk of frost. A landscape with trees can assist in preventing frost. Trees transpire a lot of moisture through their leaves.
What is the dew point? As a rule of thumb, don’t worry about a frost if the dew point (the temperature at which the air is no longer able to ‘hold’ all the moisture within it) is above 45°F on the evening weather report. The more moisture in the air, the less likely a frost. A light watering of the garden a day or two before a frost is predicted can help stop it settling.
Row covers can protect tender crops from a light frost. Photo by NataliaL/Shutterstock
WHAT’S THE DIFFERENCE BETWEEN A LIGHT FROST AND A HARD FREEZE?
A light frost occurs when the nighttime temperature drops to below 32 degrees Fahrenheit (0°C), and refers to the conditions that allow a layer of ice crystals to form when water vapor condenses and freezes without first becoming dew.
A hard freeze is a period of at least four consecutive hours of air temperatures that are below 28 degrees Fahrenheit (-2°C). Many plants can survive a brief frost, but very few can survive a hard freeze.
WHAT TEMPERATURES CAUSE FROST DAMAGE?
For many vegetables, frost causes damage and crop failure. But also there are other vegetables which actually benefit from a frost. The flavor of broccoli, for instance, actually improves if the plant has experienced a frost, while carrots get sweeter as the temperature drops.
How low can you go? The temperatures shown in the graphic below tell you when the frost will cause damage to the respective vegetable.
HOW TO PROTECT PLANTS FROM FROST
General Frost Protection Tips
Frost can hit in spring or fall in most areas. Generally, covering plants to create a temporary pocket of warmer air is the best way to protect plants.
Keep an eye on the weather forecast. If it looks like temperatures are going to drop, get ready to protect tender plants.
Make use of season extenders like row covers, cold frames, or cloches to protect tender plants, such as seedlings or warm-weather veggies. Row covers or garden fleece can be used to help create a warmer environment beneath them. You’ll need to use posts, bamboo, or flexible PVC piping to create space for the plants to grow, then drape landscape fabric or plastic over the frame; weigh down the edges with rocks or bricks or pegs so the covers do not blow away. To protect young plants from frost, use 2-liter soda bottles cut in half as cloches.
It’s best to have all covers in place well before sunset. Drape loosely to allow for air circulation. Before you cover the plants in late afternoon or early evening, water your plants lightly.
Remove any covers by mid-morning so that plants can get full exposure to the warming sunlight.
Protecting from a Spring Frost
It can be a real bummer to lose your young plants if a late spring frost hits. Here are some tips for preventing frost damage in spring:
While frosts are still possible, plant cool-season crops that are more tolerant of colder temperatures. Crops like peas, spinach, kale, and cabbage can power through a light spring frost.
Start tender or warm-season crops—like tomatoes and peppers—indoors or after the threat of frost has passed. Consult our Planting Calendar to see recommended planting dates.
Tips to Protect Your Garden From Frost
If you’re a gardener, it’s the first fall frost which is most concerning, as it can result in a lot of lost crops. Here are a few fall frost damage prevention tips:
In the fall, the first frost is often followed by a prolonged period of frost-free weather. Cover tender flowers and vegetables on frosty nights, and you may be able to enjoy extra weeks of gardening. For coverings, choose an old sheet or material that won’t damage the plants beneath. Drap loosely and secure to ground with rocks or bricks.
If you have a day or two before the frost is expected, watering the soil around the plants can help, as water holds heat better than soil. However, avoid soaking the ground as this can lead to the water freezing within the soil and damaging the roots.
Mulch your garden beds. Mulching with materials like straw, pine needles and wood chips helps preserve heat and moisture and so prevents frosts forming.
Bring houseplants (especially topicals) and other tender plants indoors before the first light frost arrives. Keep them in a sunny window in a relatively moist room; the kitchen is often best.
Before a light frost: Harvest basil and other tender herbs. Even if they survive the frost, they don’t do well in cold temperatures. The same is true for most annuals.
Before a light frost: Harvest all tender vegetables and tender greens, including: tomatoes, eggplants, peppers, beans, cucumbers, watermelons, cantaloupe, okra, squash, and sweet corn. Here are a few tips for ripening green tomatoes specifically.
For plants that can survive a light frost, add a heavy layer of mulch to keep the ground around them from freezing. You can still harvest late into the fall as long as the ground isn’t frozen. These veggies include: beets, broccoli, cabbage, celery, lettuce, parsnips, arugula, swiss chard and other leafy greens.
Harvest plants that can survive a hard frost last, such as: carrots, garlic, horseradish, kale, rutabagas, leeks, parsnips, radishes, spinach, and turnips.
Following these tips should help prevent your garden from taking too much of a hit when frost occurs!
till next time this is Becky Litterer, Becky’s Greenhouse, Dougherty Iowa email@example.com 641-794-3337 cell phone 641-903-9365