- How to Predict a Frost
- Frost And Your Plants: What You Need To Know
- A Gardener’s Guide to Frost
- What Is Light Frost: Information On The Effects Of Light Frost
- Plant Frost Info
- What is a Light Frost?
- Plants Affected by Light Frost
- About Frost
- What is Frost?
- What’s the difference between light frost and severe frost?
- Tissue Damage
- What not to do
- Potato Plant Identification
How to Predict a Frost
Learn how to predict frost, differentiate between a light frost and a hard freeze, and protect your garden from frost with these tips!
First, plan ahead. Look up the average frost dates for your area to know when frosts are most likely to occur. Use our Frost Dates Calculator to find frost dates for spring and fall in your area.
Keep in mind that frosts can vary greatly by microclimate. In fact, while you may have frost in your garden, your neighbor across the street may see no sign of it!
Consider these factors when the radio and TV reports say “frost tonight”:
- How warm was it during the day? 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.
- Is it windy? 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? If the Sun sets through a layer of thickening clouds, the clouds will slow radiational cooling and help stave off a frost.
- What is the dew point? As a rule of thumb, don’t worry about a frost if the dew point (the temperature at which water vapor condenses) is above 45°F on the evening weather report.
- How is your garden landscaped? Gardens on slopes or high ground often survive when the coldest air puddles down into the valleys and hollows.
- How far are your plants from the ground? Plants that are close to the ground have a better chance of being protected by the warmth of the earth or the foliage of neighboring plants.
- What’s your local weather forecast? Don’t get blindsided by bad weather! See our 7-day forecasts to stay up to date on the weather.
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.
Preparing for 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:
- When frosts are still possible, plant cool-season crops that are tolerant of colder temperatures. Crops like peas, spinach, kale, and cabbages 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.
- 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 young plants.
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:
- Harvest basil and other tender herbs before a light frost. Even if they survive the frost, they don’t do well in cold temperatures. The same is true for most annuals.
- Bring geraniums and other houseplants (especially tropicals) indoors before the first light frost arrives. Keep them in a sunny window in a relatively moist room; the kitchen is often best. See more about overwintering geraniums and preparing the garden for winter.
- Harvest all tender vegetables and greens before a light frost, including: tomatoes, eggplants, peppers, beans, cucumbers, watermelons, cantaloupe, okra, squash, and sweet corn. Here are a few tips for ripening green tomatoes specifically.
- Another option is to protect tender vegetables from light frosts with row covers, cold frames, old sheets, paper bags, or clear plastic containers.
- For plants that can survive a light frost, add a heavy layer of mulch to keep the ground 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! For even more tips, see Preparing Your Garden for Winter and Fall Chores: Autumn Garden Cleanup.
Be sure to check our more extensive instructions on preparing for frost as well, and let us know in the comments what you do to prepare for frost!
Frost And Your Plants: What You Need To Know
The dreaded first frost of fall looms just around the corner for many gardeners across the country. During a light frost, some plants may be killed, with little destructive effect on hardier vegetation. Here’s a guide to frost and how you can protect your plants.
Clear or Cloudy Sky?
Frost (also called white or hoarfrost) occurs when air temperatures dip below 32°F and ice crystals form on plant leaves, injuring, and sometimes killing, tender plants. Clear, calm skies and falling afternoon temperatures are usually the perfect conditions for frost. If the temperatures are falling fast under clear, windy skies-especially when the wind is out of the northwest-it may indicate the approach of a mass of polar air and a hard freeze. A hard or killing frost is based on movements of large, cold air masses. The result is below-freezing temperatures that generally kill all but the most cold-tolerant plants.
Cloudy skies: you may be in luck.
If the temperature is cool, but clouds are visible, your plants may be protected. During the day, the sun’s radiant heat warms the earth. After the sun sets, the heat radiates upward, which lowers the temperatures at or near the ground. However, if the night sky has clouds, these clouds will trap the heat and keep the warmer temperatures lower, closer to your plants, preventing a frost.
Wind also influences frost. If the air is still and windless, the coldest air settles to the ground. The temperature at plant level may be freezing, even though at eye level it isn’t. A gentle breeze, however, will prevent the cold air from settling and keep temperatures higher, protecting your plants. If the wind itself is below freezing, frost may be very damaging.
Humidity and moisture are good things when talking frost. When moisture condenses out of humid air, it releases enough heat to sometimes save your plants. When the air is dry, the moisture in the soil will evaporate. Evaporation requires heat, which removes warmth that could save your vegetables.
Location, location, location.
The location of your garden can have a tremendous influence on whether or not an early frost could wipe out your garden, but leave your neighbor’s alone. As a general rule, the temperature drops 3°F to 5°F with every 1,OOO-foot increase in altitude. The higher your garden, the colder the average air temperature and the more likely your plants will be hit by an early freeze.
However, lower isn’t always better. Cold air is heavier than warm air and tends to sink to the lowest areas, causing frost damage. The best location for an annual garden is on a gentle, south-facing slope that’s well heated by late-afternoon sun and protected from blustery north winds. A garden surrounded by buildings or trees or one near a body of water is also less likely to become frost covered.
The type of soil your garden is growing in also affects the amount of moisture it holds. Deep, loose, heavy, fertile soil releases more moisture into the surrounding air than thin, sandy, or nutrient-poor soil. The more humid the air is, the higher the dew point will be, and the less likely that frost will form on those plants. Heavily mulched plants are more likely to become frosted since the mulch prevents moisture and heat from escaping out of the soil and warming the surrounding air.
Know your plants.
The plant itself determines its likelihood of frost damage. Immature plants still sporting new growth into the fall are most susceptible-especially the new growth. Frost tolerance tends to be higher in plants with maroon or bronze leaves, because such leaves absorb and retain heat. Downy- or hairy-leaved plants also retain heat. Compact plants expose a smaller proportion of their leaves to cold and drying winds. By the same token, closely spaced plants protect each other.
Frost on its way?
If a frost is predicted, cover your plants, both to retain as much soil heat and moisture as possible and to protect them against strong winds, which can hasten drying and cooling. You can use newspapers, baskets, tarps, straw, and other materials to cover your plants. Cover the whole plant before sunset to trap any remaining heat. Be sure to anchor lightweight coverings to prevent them from blowing away.
Keep the soil moist by watering your plants the day a frost is predicted. Commercial fruit and vegetable growers leave sprinklers on all night to cover plants with water. As the water freezes, it releases heat, protecting the plants, even though they’re covered by ice. To prevent damage, the sprinklers need to run continuously as long as temperatures remain below freezing.
Cold Temperature’s Effects On Plants and Vegetation
FROST: Damage depends upon the length of frost duration.
LIGHT FREEZE: 29 degrees F to 32 degrees F / -2 degrees C to 0 degrees C. Tender plants killed with little destructive effect on other vegetation.
MODERATE FREEZE: 25 degrees F to 28 degrees F / -4 degrees C to -2 degrees C. Wide destruction on most vegetation with heavy damage to fruit blossoms and tender semi-hardy plants.
SEVERE FREEZE: 24 degrees F / -4 degrees C and colder. Heavy damage to most plants.
When is the average date for frost in your area? Check out our Average Frost dates here.
A Gardener’s Guide to Frost
Do Consider Dew
The dew point is the temperature at which the air is totally saturated with moisture. Television and radio meteorologists may state the dew point temperature during routine forecasts.
The more moisture the air contains, the higher the temperature will be when the moisture starts to condense as dew, producing heat. And, obviously, the higher the temperature, the less chance of frost. For example, a dew point of 43°F almost certainly means no frost that night.
Interestingly enough, frost is more likely to form on a dry evening when the air temperature is a warmish 50°F and the dew point is a low 33°F than when the air temperature is a cooler 43°F and the dew point is 41°F.
Eliot Tozer writes and gardens in Tappan, New York.
Photography by David Cavagnaro
6. Know Your Plants
The plant itself determines the likelihood of frost damage. Immature plants still sporting new growth into the fall are most susceptible — especially the new growth. Frost tolerance tends to be higher in plants with maroon or bronze leaves, because such leaves absorb and retain heat. Downy- or hairy-leaved plants also retain heat and reduce wind-drying of the leaves. Compact plants expose a smaller proportion of their leaves to cold and drying winds. By the same token, closely spaced plants protect each other.
What’s a Gardener To Do?
So you’ve checked the weather conditions and decide that, yes, Jack Frost is coming and protecting your plants is worthwhile. You’ll want to do two things: First, cover your plants, both to retain as much soil heat and moisture as possible and to protect them against strong winds, which can hasten drying and cooling. Use almost anything to cover plants: newspapers, bushel baskets, plastic tarps, straw, or pine boughs. Spun-bonded fabric row covers will protect plants down to 30°F, polyethylene row covers to 28°F. Cover the whole plant before sunset to trap any remaining heat. Lightweight coverings such as row covers and newspaper should be anchored to prevent them from blowing away.
Second, keep the soil moist by watering your plants the day the frost is predicted. Commercial fruit and vegetable growers even leave sprinklers on all night to cover plants with water. As the water freezes, it releases heat, protecting the plants, even though they’re covered in ice. To prevent damage, the sprinklers need to run continuously as long as temperatures remain below freezing.
And as you survey your garden’s fading glory, you may take heart from the experience of John Loudon, a 19th-century British horticulturist. Loudon stuck four stakes into a plot of grass to support a cambric handkerchief 6 inches above the surface and found that the temperature beneath it remained 9°F warmer than the temperature of the surrounding air. Yes, you can beat the frost — at least for a few nights.
2. Feel the Breeze
Wind also influences the likelihood of frost. In the absence of wind, the coldest air settles to the ground. The temperature at plant level may be freezing, even though at eye level it is above freezing. A gentle breeze, however, will prevent this settling, keep temperatures higher, and save your plants. Of course, if the wind is below freezing, you’ll probably have fried green tomatoes for tomorrow’s supper.
3. Check the Moisture
Just as clouds and gentle winds are your friends, so are humidity and moisture. When moisture condenses out of humid air, it releases heat. Not much heat, true, but perhaps enough to save the cleomes. If the air is dry, though, the moisture in the soil will evaporate. Evaporation requires heat, so this process removes warmth that could save your peppers.
4. Check Your Garden’s Location
This can have a tremendous influence on the likelihood that early frost could wipe out your garden while leaving your next-door neighbor’s untouched. For example, as a general rule, temperature drops 3°F to 5°F with every 1,000-foot increase in altitude. The higher your garden, the colder the average air temperature and the more likely your plants will be hit by an early freeze. So gardening on a hilltop isn’t a great idea, but neither is gardening at the lowest spot on your property. Since cold air is heavier than warm air, it tends to sink to the lowest area, causing frost damage. The best location for an annual garden is on a gentle south-facing slope that’s well heated by late-afternoon sun but protected from blustery north winds. A garden surrounded by buildings or trees or one near a body of water is also less likely to be frosted.
It’s late fall. The sky is blue, and the sun is bright. Then your local weather forecaster ruins everything with these chilling words: “Possible frost tonight.” Once the initial panic subsides, reason sets in. Frost is a local event, and it’s possible to predict with considerable certainty whether it will hit the plants in your garden. So relax, walk outside, and pay attention to these six signs to predict the likelihood of frost. Then, if necessary, spring into action.
1. Look Skyward
Clear, calm skies and falling afternoon temperatures are usually the perfect conditions for frost. Frost (also called white or hoarfrost) occurs when air temperatures dip below 32°F and ice crystals form on the plant leaves, injuring and sometimes killing tender plants. However, if temperatures are falling fast under clear, windy skies — especially when the wind is out of the northwest — it may indicate the approach of a mass of polar air and a hard freeze. A hard, or killing, frost is based on movements of large air masses. The result is below-freezing temperatures that generally kill all but the most cold-tolerant plants.
But if you see clouds in the sky — especially if they are lowering and thickening — you’re in luck. Here’s why. During the day, the sun’s radiant heat warms the earth. After sunset, the heat radiates upward, lowering temperatures near the ground. However, if the night is overcast, the clouds act like a blanket, trapping heat and keeping air temperatures warm enough to prevent frost.
5. Scrutinize the Soil
Your garden’s soil type can affect the amount of moisture it holds and the plants’ ability to withstand cold weather. Deep, loose, heavy, fertile soil releases more moisture into the surrounding air than thin, sandy, or nutrient-poor soil. The more humid the air, the higher the dew point and the less likely that frost will form on those plants. Heavily mulched plants are more likely to be frosted, since mulch prevents moisture and heat in the soil from escaping and warming the surrounding air. (Light-colored mulches such as hay or straw have the additional disadvantage of reflecting sunlight and heat during the day.)
What Is Light Frost: Information On The Effects Of Light Frost
Nothing takes the smile off of a gardener’s face quicker than an early fall or a late spring frost. Even worse is the fact that it doesn’t take much of a frost to damage your prized plantings. Keep reading to find out what is light frost and plant frost info for plants affected by light frost.
Plant Frost Info
Understanding the frost dates in your gardening region is critical to maximizing your garden potential. However, there are always frosts that sneak up and catch you off guard, no matter how prepared you think you are.
Paying attention to weather forecasts in the fall and spring is essential to the health of your garden. Even a light frost can cause extreme damage to young spring plants or bring the colorful display of late summer tender plants to a screeching halt.
What is a Light Frost?
A light frost occurs when the air has dropped below freezing but the ground has not. A hard frost occurs when the air is cold and the ground is hard. Many plants can survive the occasional light frost, but more care must be taken when the weather forecast calls for a hard frost.
The effects of light frost vary from plant to plant but can include a browning or scorching effect on foliage, all the way to a complete stem collapse. Therefore, it’s usually a good idea to provide all your plants with some light frost protection.
Plants Affected by Light Frost
Tender plants can be killed by a light frost; these include tropical and subtropical varieties. When the water inside of the plant gets cold, it crystallizes. When it warms up, it cuts the inside of the plant, allowing moisture to escape and thus, killing the plant.
If the area between leaf veins appears pale brown or scorched, it may indicate frost or cold damage. Tender and tropical perennials and bulbs may turn black when hit with the first fall frost.
Light frost protection is definitely a necessity if you have tender plants in your garden. Spring frosts can cause damage to tree blossoms and young fruits. Frost-sensitive vegetables such as potatoes and tomatoes may suffer leaf scorch, browning and even death from a late spring frost.
Ice crystals form at temperatures below 32°F, when water vapor condenses out of the air and settles on a cool surface, such as your garden beds or garden plants. Frost is just a frozen form of dew, and it damages plants by freezing the water inside the plant cells, which then burst and die.
A light frost can occur at 30-32°F. There’s a touch of white on the ground, but it’s short-lived; as soon as the sun hits it, it’s gone, and all but the most frost-sensitive plants will survive. At lower temperatures, a killing frost can occur, and you can pretty much say good-bye to most of your annual flowers and most vegetables.
When frost threatens…
Crops differ in their susceptibility to frost, and there are steps you can take to extend the season. These maneuvers are worthwhile, because typically a frost is followed by some warm, sunny weather before things really chill down for good.
If a light frost is predicted, I cover my frost-sensitive crops with assorted bed sheets and light blankets (never use plastic) and hope for the best. The next morning, anticipating rising temperatures, I remove the coverings.
If you don’t cover your plants and frost hits them, you can sometimes save them by hosing off the frost early in the morning before the sun hits them.
What to harvest when…
If you’re like me, you’ll want to keep your garden going as long as you can. So you won’t want to put your garden to bed until it becomes absolutely necessary.
The measures described above work for a while, but at a certain point, enough is enough. Even if the plants are alive, they are no longer actively producing. When a hard frost is imminent, I bow to the inevitable. I harvest all remaining tomatoes (ripe or not), cucumbers, hot peppers, sweet peppers, eggplant, beans, and basil, along with any frost-sensitive flowers I’d like to enjoy a bit longer in a vase.
No need to harvest the winter squash and pumpkins yet, as these survive just fine in the field even if the vines die. Leeks, scallions, beets, and carrots are in no danger from frost either, and members of the cabbage family—brussels sprouts, broccoli, and kale—actually improve in flavor with frost.
The Farmer’s Almanac indicates that the average killing frost date for our area is October 11th but that info won’t help with anticipating light frosts so it pays to keep an eye on nighttime temperatures.
“Clear moon, frost soon.”
Ever hear that saying? It’s telling you that on a clear night, in fall, winter, or spring when you can see the moon, frost is likely to occur. This is because there is no wind to mix ascending warm air with descending cold air and there are no clouds to radiate heat back to the earth. There are other factors that influence whether or not your plants will experience frost, so let’s understand what causes frost to form.
What is Frost?
Frost is frozen water that has condensed from water vapor in the air. For frost to occur, surface temperatures must be below freezing (otherwise you would see dew, not frost). Frost forms on plants when they are colder than the dew-point temperature of the surrounding air.
What’s the difference between light frost and severe frost?
Frost is rated by the severity of the frost layer. The higher the dew-point temperature, the more water is in the air, and the higher the rate of frost accumulation. Light frost will damage smaller plants more than larger, established plants. Severe frost will damage and even kill most plants that are not dormant.
Classification of freeze temperature is usually based on its effect on plants. A light freeze is 29°F to 32°F — tender plants are killed with little destructive effect on other vegetation. Moderate freeze is 25°F to 28°F — widely destructive to most vegetation, with heavy damage to fruit blossoms and tender and semi-hardy plants. Severe freeze is 24°F and colder — damage to most plants.
The lower the temperature, the longer the exposure, and the faster the temperature drops, the greater the damage to the plant. Therefore the heaviest damage from low temperatures generally occurs in late spring, early fall, or any time cold temperatures occur after a warm winter period.
Common types of damage include:
- death of dormant flower buds
- dieback of overwintering broad-leaved plants
- frost damage to tender shoots, flowers, and fruits
The effects of temperature vary with plant species, stage of growth, age, general health, and water content. Young, actively growing, flowering, and/or dehydrated plants tend to be most vulnerable. Actively growing foliage is very susceptible to frost damage. If a freeze occurs when there has been no prior cold weather to “harden off” a plant, the damage will be more extensive.
Protect plants by:
- applying water or heat
- increasing air circulation
Cover plants with cloth or paper (not plastic) to insulate. Sheets or blankets provide minimal protection and can crush plants. A properly applied frost cloth can protect plants at temperatures down to 20° F depending on the fabric and the weave. Completely drape the plant from top all the way to the ground (or around container.) Do not allow any openings for warmth to escape. This procedure will trap the heat radiating from the soil and maintain a more humid atmosphere around the plant foliage.
Some of the frost cloths available (including Frost Protek™ plant covers) may be left on for extended periods without risk of harming the plant. If you use sheets or blankets, remove the coverings every morning when the temperature under the covering warms to 50° F. Permanently covering plants with sheets or blankets for the duration of the winter can be harmful and is not recommended. Even if the temperature under the drape does not warm up enough to “cook” the plant, it is possible to warm up enough to cause the plant to break dormancy, begin actively growing, and thus become more susceptible to frost damage.
Place in protected locations
Western and southern exposures tend to be warmest. Block walls, rocks and patios collect and reflect the heat of the sun. Firm, bare, moist soil absorbs more heat and loses it more rapidly than soil that is loose, dry, or covered with mulch or vegetation.
Keep plants well watered. Frost injury occurs when ice crystals form on the leaf surface drawing moisture from the leaf tissue. The damage from this dehydration will be less severe if the plant is not already drought-stressed. It is best to keep the moisture level as even as possible.
100-watt electric light bulbs, in an approved outdoor fixture, can provide supplemental heat to covered plants, if needed. Be sure to hang them below the foliage, allowing the heat they generate to rise (within the covered area) and warm the plant. Take care that the bulb is not so close to the trunk, branch, or cover that it could burn.
Using mulch has good and bad points. It insulates against fluctuating surface soil temperatures and guards against too much daytime warm-up that, in turn, would activate plant growth and increase freeze risk. However, it also prevents the capture of heat that could be harnessed to protect a frost sensitive plant.
What not to do
Do not use plastic to cover plants. Plastic is a poor insulator and can harm foliage. Do not prune or throw away frost-damaged plants until they begin growing in the spring. Pruning might stimulate new growth which would be vulnerable to late frosts. The frost-damaged leaves and stems will continue to help trap warm air within the canopy. In addition, the damage is often not nearly as bad as it initially looked; new growth may come out of tissue that you thought was dead. Only after new growth starts in the spring should you prune out dead wood.
Potato Plant Identification
potato plants image by aprilira from Fotolia.com
It’s difficult to watch your potatoes grow, since the tubers grow underground. Gardeners can learn to identify the leaves, shoots and stalks of their potato plants to monitor the plant through the growing season. Potatoes themselves should be familiar, but some gardeners may be surprised at the array of types of potato plants that exist.
Potato tubers grow underground. The stalks and leaves that appear above ground are dark green. Potato plants develop pale purple or pink flowers with a yellow center that will produce seeds.
While potatoes can be grown from true seed, the typical “seed” is actually a small piece of potato tuber with at least one “eye.” Gardeners should purchase seed potatoes rather than use cut-up store-brought potatoes for seed. Seed potatoes can be small whole potatoes or chunks of cut potato that weigh 1-1/2 to 2 oz. each.
True potato seed comes from the potato plant flowers. These flowers produce berries containing hundreds of small seeds. The seeds can be planted directly in the garden bed three to four weeks before seed potatoes are planted and will yield potato plants.
flowering potato bush image by Alina Goncharova from Fotolia.com
Potato leaves are flat-edged and nearly oval-shaped with a point on the end. The leaves grow off both sides of the stem and are dark green with pale green veins.
Potato plants take two to four weeks to emerge from the soil once they’ve been planted from seed potato. If you’re unsure whether you’ve got a weed or a potato growing in your garden, watch the plant’s development: A potato plant has a vining habit and will display vining tendrils. The plant quickly develops several branches that display the ovoid potato leaves.
Gardeners can choose potatoes that produce tubers with red, blue or yellow skin and pale white, creamy white or purple flesh.
GENERAL INFORMATION: Two pounds of seed potatoes will produce fifty pounds of potatoes for eating. Potatoes need loose, fast-draining soil; tubers become deformed in heavy, poorly drained soil.
PLANTING: The location of potatoes in your garden should be rotated on at least a three year schedule. Add compost to the soil and plant Alfalfa, Beans, Peas, or Peanuts during the interim years (Peanuts can be obtained from bird specialty shops). Potatoes grow best in an acidic soil (pH5.5-6.5); therefore sulfur should be added to the soil in the Bay Area at about 1.5 pounds per 100 square feet and gypsum at a rate of 5 pounds per 100 square feet. A 5-10-5 fertilizer (‘Bulb Food’) should be applied at planting time and again when the plants are 4 to 6 inches high. Organic grower can substitute cottonseed meal. Potatoes can be planted between November and February.
If you have a heavy clay soil, amend it with two to three inches of Gold Rush or Bumper Crop dug to a depth of 8 to 10 inches or fill a raised bed with “Nursery Mix”.
The above ground potato plant is sprawling, bushy and dark green with much-divided leaves somewhat like Tomato plants. Clustered inch-wide flowers are pale blue. Round yellow or greenish fruit is rarely seen.
If using full grown Potatoes, cut Potatoes into chunky pieces with at least two eyes. These pieces should be 1 1/2 to 2 inches square. U.C. Extension recommends that you dust the chunks with sulfur and let them heal overnight. We have found that you can skip the sulfur dusting and then allow several days for the cut surface to dry. Place chunks 4 inches deep, 12 to 18 inches apart and 24 inches between rows. Small whole Potatoes are preferable and are planted the same way.
Potatoes must be ‘hilled’ as they mature. About the time the flowers first appear, you may notice the ground bulging at the base of the plant. Scrape some soil from between the Potato plants and form a hill around the base of the plant to keep the Potatoes covered. This will have to be repeated several time to prevent the Potatoes from getting sunburned (skin turns green and is poisonous) as the Potatoes enlarge in the ground.
WATERING: Do not plant if soil is very wet. After top growth appears, give plants a thorough soaking every week or two (so that the soil is moist down to about 12 inches). Potatoes don’t need a lot of water.
DIGGING: Dig early (or new Potatoes) when tops begin to flower; dig mature Potatoes when tops die down. Dig Potatoes carefully using a spading fork to avoid bruises and cuts.
In 40 to 60 days early Potatoes will bloom. This is the time to carefully poke around the Potato hill by hand to see what you can find. Small Potatoes removed at this time are called ‘new Potatoes.’ Leave enough Potatoes to mature to full size.
For the main crop you can either let the first frost kill the vines (spring-planted Potatoes) or you kill them yourself by excluding all water or cutting off the tops. Once the vines have died the Potatoes need to be left in the ground for two weeks. The skins will toughen and cure to prevent scuffing and bruising. Then you may start harvest.
WEEDING: Weed carefully and thoroughly. There should be no weeds in the Potato bed.
STORING: Potatoes are best stored at 36-40 degrees in a dark environment with ventilation and high humidity. Well stored Potatoes can last up to six months. Small Potatoes (up to 1 1/2 inches in diameter) can be saved and planted next year.
Tips for Planting
- Plant only certified potato seed, preferably from a local seed producer.
- Plant potato seed when the soil temperature is 10˚C or warmer. Planting into cold soils encourages seed rot and other diseases.
- Rather than planting early into cold soil, try ‘green sprouting’ or ‘chitting’ your potato seed. Approximately, 4 weeks prior to the normal planting date, place your seed at 20˚C in the dark until you start to see sprouts beginning to emerge – then move the tubers into a spot where they will receive 10+ hours of gentle light each day. After about 2 weeks of this treatment, the seed tubers will form short, stubby green sprouts that will stay intact during planting and give you a headstart on the early emergence of your potato crop.
- Emerging potato plants are frost-sensitive but following a frost event, the plants will eventually regrow from stems protected under the soil.
- Planting small whole potato seed tubers is preferred to cutting larger seed. If you must cut larger tubers into seed, ensure that there is at least one live sprout/seed piece.
- Plant potato tubers 10-15cm deep. For irrigated potatoes, place tubers 30cm apart within the row and 1m apart between rows. For dryland potatoes, increase in-row spacing to 45cm.
- Form small hills of soil over tubers at planting time. When plants emerge, hoe up soil around the potato plant being careful not to cover the emerging plant. Two to three weeks later (late in June), pull more soil from between the rows to expand the hill around the plant. The potato plant should be growing in the lower centre of an ‘M’ shaped hill. Hilling plants will encourage tuber production along the underground stem.
Recommended Growing Conditions and Practices
- Potatoes prefer sandy loam to loam soils for good tuber production.
- Although potatoes produce well in fertile soils, too much nitrogen, especially early in the season, will encourage excessive top growth at the expense of tuber set.
- Make sure any manure added to your garden is well composted. During the composting process, microorganisms convert nutrients in the manure into usable forms for the plants. Uncomposted manure can contain high levels of certain nutrients, like nitrogen, that can burn plant tissue. Uncomposted manure can also contain bacteria like E. coli, which is not something you want on your fresh vegetables.
- A steady supply of soil moisture will promote the production of a vigorous potato crop capable of producing optimum yields of well-shaped tubers. Irrigate actively growing potato plants 2.5cm water/week
- Keep the potato patch weed free to produce maximum yields and to reduce problems with disease and pests like aphids and Colorado potato beetles.
- Potatoes can be harvested as soon as the tubers reach the desired size for eating.
- Removing the potato tops at least one week prior to harvesting encourages good skin set on the tubers. Good skin set ensures that the tubers will resist dehydration and disease during subsequent storage. If the tops have been frozen or have senesced naturally prior to harvest there is no need to remove the tops prior to harvesting.
- Should I dry my harvested potatoes in the sun? Allowing freshly harvested potatoes to briefly dry in the field will help in the removal of adhering soil. However, more extended exposure to sunlight is not recommended. Light, of any kind, encourages the potato to turn green and produce glycoalkaloids which give the potato a bitter flavour.
- Are green potatoes poisonous? Potatoes tubers turn green after significant exposure to light. The green colour indicates chlorophyll synthesis. While this may indicate the presence of glycoalkaloids, usually these glycoalkaloids are located just beneath the tuber skin. By peeling away the green skin and underlying green flesh, the tuber should be safe to eat. If the potatoes taste bitter, they may be high in glycoalkaloids. Cooking at temperatures higher than 350˚F partly destroys glycoalkaloids. When in doubt – throw it out.
- Ideal storage conditions for potatoes are about 4˚C and 90-95% humidity with regular air exchanges.
- Black spots in the potato flesh indicate a lack of oxygen to the tuber tissues, resulting in cell death. Tubers exposed to flooding during growth or insufficient air exchange/oxygen supply during storage commonly show this disorder.
- Do not store apples next to potatoes. The ethylene from the apples will cause the potatoes to sprout.
- Hollow heart in potatoes refers to a spot of brown flesh or a hollow area in the centre of the potato. Hollow heart is caused by rapid fluctuations in growing conditions – such as sudden and extreme fluctuations in field temperatures or heavy rain after several weeks of drought. Potato cultivars, like Viking and Shepody, which tend to produce only a few large tubers are more prone to ‘hollow heart’ than other potato cultivars.
- Knobby potatoes refer to knobs or outgrowths forming off to the side of the main tuber. Like hollow heart, this disorder is caused by fluctuating growing conditions i.e. hot and dry followed by cool and wet. The cultivar Russet Burbank is very prone to knobby growth.
Colorado Potato Beetle(CPB) (Leptinotarsa decemlineata)
- Adults overwinter in the soil in the previous year’s potato fields or in surrounding grassy areas.
- Overwintering adults appear in the late May or early June; feed for a few days on the emerging potato crop and then mate.
- Individual females lay 300-500 eggs from June to late July. These eggs will be found in yellow clusters on the underside of potato leaves.
- Once the eggs hatch, larvae appear as 3-5mm long yellow-orangey red soft-bodied organisms. The larvae feed heavily on the leaves for the next 3-5 weeks and then burrow into the soil.
- Pupation occurs in the soil and new adults emerge in 1-2 weeks.
- The new adults feed for a few days and then begin to look for a protected spot to hibernate through the coming winter.
- In Saskatchewan, there is usually only one generation of Colorado potato beetle per growing season.
- Whenever possible, avoid growing potato plants in or near the same area of the garden for a minimum of three years.
- Pick the first flush of adult beetles by hand – this will reduce eggs laid, larvae and the number of adult beetles later in the season.
- Rototill in fall to expose the overwintering adult beetle to cold and dehydration.
- For larger gardens, consider digging a plastic-lined trench around the potato patch. The beetles will become trapped in the plastic-lined trench as they are unable to climb the steep, slippery walls of the trench.
Wireworms (Agriotes sp.)
- Tunnel into potato seed pieces and developing tubers.
- Holes that look like a sharpened pencil has been stuck in the potato are characteristic of wireworm damage.
- Potato wireworm infestations can be especially problematic in newly broken land that was previously in prairie or sod. To determine the level of wireworm infestation in a new potato patch, place carrot pieces, buried 10cm deep, throughout the area you plan on planting to potatoes. After three or four days, dig up the carrot pieces and count the number of wireworms. If an average of one or more wireworms is encountered per station, damage to the coming potato crop can be severe.
- To prevent wireworm infestations, avoid planting in newly cultivated soils.
- Employ a minimum three-year rotation with crops such as corn and beans.
- Minimize irrigation in infested soils as wireworms do poorly under dry soil conditions.
- Rototill the potato plot deeply (10cm+) and late in the fall to expose overwintering larvae.
- Wireworm problems in the typical garden tend to decline with time, as the wireworms move out of the garden and into other more preferred food crops such as grasses.
- Common scab (Streptomyces scabies) is a bacteria type organism that causes the formation of roundish, irregular, brown lesions on the tuber surface. As the name suggests, the lesions resemble scabs.
- Powdery scab (Spongospora subterranea) is a fungal disease characterized by smaller and rounder warty, raised lesions on the tuber surface. The scab lesions caused by powdery scab are very similar in appearance to common scab – and the two diseases can only be accurately differentiated under the microscope. Both types of scab can survive in the soil for many years.
- Neither type of common scab causes any loss in yield or quality of the potato crop – aside from their negative impact on tuber appearance.
- There are no chemical treatments for either type of scab and the best way to avoid scab is to prevent it from entering your garden by:
- Purchasing only certified, scab-free potato seed.
- Placing your potato patch in a minimum 3 year (preferably 4-5 year) rotation with other vegetable crops.
- Scab problems may be exacerbated by high organic matter content in the soil; ensure that all organic matter and manure is well composted before adding it to garden soil.
- If common scab is a problem, try irrigating slightly more than normal, especially when the crop is just setting tubers (hint – this occurs when the crop is starting to flower). By contrast, if powdery scab is a problem, avoid over-irrigating your potato patch.
- Grow potato cultivars that are resistant or less susceptible to scab.
Resistant cultivars: most russets (ex. Russet Burbank, Russet Norkotah, Goldrush), Viking (red skin), Norland
Susceptible to scab: Shepody, Yukon Gold, Pontiac, Sangre
Rhizoctonia or Black Scurf (Rhizoctonia solani)
- When potatoes are planted into cold wet soil, this soil and seed-borne fungal disease attacks the emerging sprouts, resulting in slow crop emergence and development of a small weak plant. If cool wet conditions persist into the growing season, Rhizoctonia affected plants produce reddish-brown stems with rolled purple/red leaves. They may eventually begin to form tubers above the soil surface.
- As the potato crop matures, the Rhizoctonia fungus produces black resting spores on the surface of the tubers. These spores resemble soil – but as they adhere tightly to the surface of the tuber they look like “soil that won’t wash off”.
- Plant certified seed tubers that are free from Rhizoctonia. Grow potatoes on a minimum three rotation in the garden; do not include any other solanaceous crops in that rotation (ex. Pepper, eggplant); plant tubers into warm, dry soil where there will be rapid emergence; delay irrigation until the crop has emerged.
- Harvest as soon as the crop is mature as the severity of Rhizoctonia infection of the tubers increases rapidly once the tops begin to die-back.
- Tubers affected by Rhizoctonia may not be attractive, but they are edible
- Can be caused by several different organisms that naturally occur in the soil.
- Soft rots most commonly invade tubers through the cuts and bruises that occur during harvest. Potatoes damaged by frost or flooding are also susceptible to attack by soft rot bacteria.
- Development and spread of soft rot depends on warm moist conditions.
- Grow potatoes in well-drained soils. Time the harvest so the crop is lifted during cool conditions (ie; less than 10oC) but well ahead of heavy frost. Harvest carefully to avoid damage to the tubers. Store only mature tubers with good skin set. Hold freshly harvested potatoes for a week or so at 10oC to promote wound healing – then cool to the final storage temperature of 4oC. Maintain steady air flow through the potatoes during wound healing and long-term storage. If washing potato tubers prior to storage, use clean, cool water and ensure that potatoes are dry prior to storing.
Dry Rot (Fusarium sp.)
- The Fusarium fungus causes the development of a slow-growing greyish/black dry rot in stored potatoes.
- The best way to prevent dry rot is to be very careful during harvest, as this disease can only gain entry to the potato through a wound.
- Maintaining low temperatures throughout the storage period will slow but not stop the development of the dry rot.
Early Blight (Alternaria solani) vs Late Blight (Phytophthora infestans)
Early blight is a common disease among potatoes and other solanaceous crops like tomatoes.
- Symptoms of early blight include small, brown, lesions consisting of concentric rings. The lesions take on an angular shape as they are limited by the leaf veins. Pale yellow margins often border the lesions. Early blight is typically seen first on the older, lower leaves. While early blight typically shows up late in the growing season every year in Saskatchewan, it rarely has any impact on yields or crop quality.
Preventing early blight
- Management practices that keep the potato crop healthy and vigorous will also protect it against early blight. Plant high quality certified seed into fertile soil and keep the crop well watered.
Late blight also affects potatoes and other solanaceous crops. While late blight is not as common in Saskatchewan as early blight it is a much more devastating disease when it does occur.
- Symptoms of late blight include: lesions appear on older leaves following several days of warm, wet or humid weather. Late blight lesions begin as dark green, water-soaked areas at the leaf tips. A yellowish-white halo will often surround these lesions. The lesions grow rapidly and do not stop at the leaf veins. A white fungal growth can sometimes be detected on the underside of infected leaves, especially on dewy mornings. Under wet, warm conditions, late blight spreads rapidly and can kill an entire potato patch in a few days. Tubers at or near the soil surface will be infected by late blight spores. Tubers infected with late blight display sunken lesions (especially around the eyes) that become reddish and granular. Soft rot bacteria quickly invade late blight damaged tubers, turning the entire potato storage into a mushy, rotting mess.
Preventing Late Blight:
- Late blight can only overwinter on the Canadian Prairies in living potatoes. Infected tubers culled from the crop should be buried or frozen. Never plant potato tubers that are suspected of carrying late blight.
- Potato plants infected by late blight should be immediately removed from the garden and buried. Tubers not affected by rot can be eaten.
- As there have been incidences of greenhouse-grown tomato transplants spreading the late blight fungus early in spring: ensure that your tomato transplants are grown by a reputable greenhouse grower.
- Foliar copper sprays can help prevent late blight infection but are useless once a late blight infection becomes established. The sprays must be re-applied immediately after every rain/irrigation event.
Early Blight (Alternaria solani)
Late Blight (Phytophthora infestans)
Is commonly found in Saskatchewan gardens on an annual basis.
Historically, is not very common in Saskatchewan gardens.
Progresses slowly during the season. Unless it is a severe case, it does not affect tuber yields or storage.
Spreads very quickly through the potato patch once it has established. Plants die quickly and tubers usually rot in storage.
Small brown lesions that are angular in shape and limited by leaf veins. The lesions eventually are surrounded by concentric rings.
Late blight lesions begin as dark green, water-soaked areas at the leaf tips. The lesions grow rapidly and do not stop at the leaf veins. Lesions are often surrounded by a yellowish-white halo. A white fungal growth can sometimes be detected on the underside of infected leaves, especially on dewy mornings.
Lesions are typically found first on older, lower leaves.
Lesions appear on older leaves on the outer surface of the plant following several days of warm, wet or humid weather.
Is commonly found in the environment and does not necessarily carry over on potato seed.
Overwinters on the Canadian Prairies in living potatoes. (i.e. potato seed) Plant clean, certified, locally grown potato seed.
POTATO CULTIVAR INFORMATION
Every potato cultivar has been bred for a particular purpose. For example, boiling potatoes don’t necessarily fry well and baking potatoes don’t necessarily boil well.
Boiling potatoes usually have a high water content and waxy texture so that they don’t turn ‘mushy’ during the boiling process.
- Norland – red-skinned, white-fleshed, oval potato recommended for boiling. Early maturing with good yields. Well suited to Saskatchewan soils and growing conditions.
- Viking – red-skinned, white-fleshed, oblong-round recommended for boiling. Early maturing. Produces a limited number of tubers/plant so the tubers tend to be very large.
- Purple Viking – purple-skinned, white-fleshed, oblong-round cultivar recommended for boiling. Slightly later maturing than Viking. Tubers tend to oversize. Yields are lower than Norland.
- Caribe – purple-skinned, white flesh, oblong potato that matures in mid-season. Yields tend to be slightly lower than Norland. Sensitive to scab.
- Sangre – dark red-skinned, white-fleshed, oval potato recommended for boiling. Mid-season maturing with average yields. Tubers are slow to oversize. Sangre is more susceptible to scab than Norland or Viking.
- Peregrine Red – relatively new, dark red-skinned, white-fleshed oval potato recommended for boiling. Mid to late season maturing with excellent tuber set and good yields. Tubers do not oversize and the tubers store better than Norland. Peregrine Red is more susceptible to scab than Norland or Viking.
- Pontiac –red-skinned, off-white fleshed oval-round potato. This variety has been around for many years. Pontiac matures slowly and tends to produce oversize tubers. Pontiac is very susceptible to common scab.
- Bintje – a white-skinned, yellow-fleshed oval potato. This mid to late-season maturing cultivar has medium-sized tubers with average yields. Taste is excellent and it is recommended for boiling.
- Shepody – a white-skinned, off-white fleshed, oblong potato recommended for boiling, baking and frying. Shepody matures early to mid-season. Oversize tubers are prone to hollow heart. Shepody is high yielding and has good flavour but is very susceptible to a range of diseases including scab.
Baking potatoes have a higher level of solids in their flesh, resulting in a firm dry texture after baking.
- Russet Burbank (a.k.a. – Netted Gem) – a russet-skinned, off-white fleshed, oblong potato that is recommended for baking and French frying. As Russet Burbank matures slowly its yields and quality can be disappointing in a short or dry growing season. Russet Burbank is susceptible to hollow heart and knobbiness, especially if the growing conditions fluctuate. Russet Burbank is resistant to scab.
- Russet Norkotah – a dark russet-skinned, uniform, oblong potato with off white flesh. Russet Norkotah matures mid-season and produces excellent yields of very uniform sized potatoes. Russet Norkotah shows little hollow heart or knobbiness. The flavour of Russet Norkotah flavour is not as good as other baking cultivars – especially after long-term storage. Russet Norkotah is resistant to scab.
- Goldrush – a russet-skinned, oblong potato with off-white flesh and good flavour. Goldrush matures in mid-season and yields are excellent. Goldrush is very resistant to scab and is recommended for baking.
- Yukon Gold – a white-skinned, yellow fleshed, round to oblong potato recommended for baking and frying. Yukon Gold matures early and tubers tend to oversize. Yukon Gold has good flavour. Yukon Gold tubers tend to rot easily if damaged and it is very susceptible to scab.
Fries/Chip potato cultivars have a high percentage of solids in their flesh and low sugar content. The high solid content insures the potatoes will stay crisp after frying while the low sugar content prevents the potatoes from becoming too dark when fried.
- Shepody (see above)
- Yukon Gold (see above)
- Atlantic – a light russet skinned, oval potato with off-white flesh. Atlantic matures in mid-season and yields are excellent. Atlantic is recommended for potato chips, French fries and baking.
- Cal White – a white-skinned, oblong potato with off-white flesh. Cal White matures mid to late season with excellent yields. Plants tend to produce fewer tubers/plant resulting in a tendency for oversize tubers. Closer plant spacing (i.e. 20cm) between seed tubers is recommended to minimize oversize tubers. Cal White is recommended for frying and baking.