coldest temperature for raspberry plants

If you are growing raspberry plants in your yard, you might be wondering if they can survive frost in winter. After all, it’s a lot of work to plant and care for raspberry plants just to lose them to the cold! So, can raspberry plants survive frost in winter? Raspberry plants can survive frost in winter, and some can take temperatures down to -35 degrees Fahrenheit (-37 degrees Celsius). However, frost and cold temperatures can hurt raspberry plants in early fall before they go dormant, or in late spring after they break dormancy. The cold tolerance of raspberry plants depends on the variety and on environmental conditions. Of course, if you know that an unseasonable cold spell or frost is coming, you can take some steps to protect your raspberry plants. In this article, we’ll look at the cold tolerance of raspberry plants, which varieties are most cold hardy, and how to provide extra cold protection. Let’s get started. Can Raspberry Plants Survive Frost in Winter? Raspberry plants can survive frost during the winter. Of course, this assumes that the plant is in the dormant state (dormancy), which protects it from cold. Raspberry plants need to be in a dormant state to survive colder temperatures. Dormancy is a survival strategy used by plants to help them survive adverse conditions, such as extreme winter cold. Plants rely on signals from the environment (such as shorter day length and colder temperatures) to tell them when to enter dormancy. An early fall frost (before the plant enters dormancy) or a late spring frost (after the plant breaks dormancy) can cause cold damage. Cold and frost can also damage flowers that appear too early in spring. In order to enter dormancy, raspberry plants first enter a rest phase, where they stop growing. Later, they enter dormancy after being exposed to enough chill hours. A chill hour is an hour during which a plant is exposed to temperatures between 32 and 45 degrees Fahrenheit (0 and 7 degrees Celsius). According to the Penn State University Extension, most raspberry plants need between 800 and 1000 chill hours to enter dormancy. If a raspberry plant does not get enough chill hours before a fall frost, cold will damage the plant. If a plant gets too many chill hours early in the season followed by unseasonably warm weather, it can be fooled into breaking dormancy too early. An early fall frost can damage a raspberry plant before it enters dormancy. According to the Penn State University Extension: “Winter injury usually occurs during mid-winter when several warm days are followed by a cold snap.”https://extension.psu.edu/small-fruit-cold-hardiness-winter-injury-in-brambles So, in short: raspberry plants need enough chill hours in order to enter dormancy, which protects them from frost during winter. You can learn more about chill hours (and why plants need them) in my article here. How Cold Can Raspberries Survive? According to Penn State University, many raspberry varieties can survive temperatures as low as -25 degrees Fahrenheit (-32 degrees Celsius). Of course, healthy canes without damage from pests or diseases are much more likely to stand up to such extreme cold. As strange as it may seem, cold injury to raspberry plants is more likely during winters without much snow. This is because a layer of snow normally acts to insulate the crowns (the base of the raspberry plant, which grows in the soil) and protect them from cold. A layer of snow can provide insulation to protect the crowns of raspberry plants from cold and frost. The variety of raspberry plant also has an effect on cold hardiness. According to the University of Maine Extension, red and yellow raspberry plants can withstand colder temperatures than black or purple raspberry plants. In areas with extreme cold temperatures (such as Maine or Vermont), fall bearing (ever bearing) raspberries may be more susceptible to cold. This is because these varieties continue to produce flowers and fruit into the fall, whereas summer bearing raspberries do not. Of course, raspberry plants have to be “ready” for winter in order to withstand cold temperatures. Environmental factors such as day length and chill hours tell them when to enter dormancy as protection against cold. Raspberry plants will gradually prepare themselves for winter cold and frost through a process called cold acclimation. According to Penn State University: “Cold acclimation" is the process by which plants develop cold hardiness … In mid-summer raspberries shoots are killed at about 18°F. During the fall, the leaves sense the shortening days and this induces the first stage of cold acclimation and by Mid-October the plants can withstand about 10°F. The second stage of acclimation is induced by temperatures just above or below freezing. As a result of a mild frost, the cold hardiness of woody plants can increase by 6 to 10 degrees within 24 hours. By early November raspberries can withstand about 1°F and by early December they can survive -10°F to -35°F depending on the variety.”https://extension.psu.edu/small-fruit-cold-hardiness-winter-injury-in-brambles As you can see, there is a huge variation in the temperatures that raspberry plants can withstand (18 degrees Fahrenheit all the way down to -35 degrees Fahrenheit). It all depends on the variety and the time of year, which determines how acclimated they are to the cold. According to Penn State University, you can tell that your raspberry plants were injured by cold if: The tops of the canes die backYou see dead buds in the spring In general, 30 to 32 degrees Fahrenheit (-1 to 0 degrees Celsius) is the threshold for damage to raspberry flowers. So, a late spring frost can destroy any chance of fruit if your plants have already broken dormancy and produced flowers. Can Raspberries Survive Spring Frost? Raspberries that are still dormant should be fine during a spring frost. However, even plants that have broken dormancy still have a chance to survive a late spring frost. How to Protect Raspberries from Frost There are several steps you can take to protect your raspberry plants from frost. You can check out all kinds of cold protection resources on this page. One factor that can make a difference in cold protection is the location you choose. Plant on a Slope or Hillside According to the University of Wisconsin Extension, you should plant raspberry bushes on a slope or hillside. That way, the heavier cold air can move down the slope and settle at the bottom of the hill, away from the plants. A hill or slope is a good place to plant raspberry bushes to protect them from cold. If you are buying new raspberry plants, you can place them wherever there is a hill or slope in the yard. For established plants, transplant any suckers that appear, and eventually you will have a whole new raspberry patch in another location. Cover Raspberry Bushes before a Frost Be sure to check the weather forecast in both the spring and fall. If a late spring frost or early fall frost is approaching, consider using row covers to protect raspberry bushes. A row cover is a long piece of material that protects plants from cold and pests, while still allowing water and sunlight to get through. You can see an example of a row cover material on the Gardener’s Supply Company website. A row cover protects plants from cold and pests. You can use hoops or stakes to hold up a row cover. Be sure to use a row cover that does not cling to your plants. Otherwise, it can actually make cold damage worse. You can avoid this “clinging” problem by using hoops or stakes to support the row covers and keep them from touching your plants. Keep in mind that row covers are only good for 3 to 4 degrees of cold protection in calm weather, and even less in windy conditions. However, it could make the difference on a cold night, so it’s worth considering. Cover Canes with Mulch Another way to protect raspberry plants from frost is to cover them with mulch. Mulch provides extra insulation against cold, which can make all the difference for your plants. According to the Penn State University Extension: “Air temperature close to the ground is often much colder (as much as 5°F) than the low temperature reached at the typical eye-level height where we usually post our thermometers, and if your field is in a low spot, may be even colder.”https://extension.psu.edu/frost-and-freeze-damage-on-berry-crops Mulching at the base of your raspberry plants will help to protect the crowns from cold in the absence of snow (which normally serves as insulation). A layer of mulch will help to protect the crowns of raspberry plants from frost. If you want extra frost protection, you can go another step further with mulch. According to the Colorado State University Extension: “Lay the canes down in one direction and hold them in place with a shovelful of soil on their tips or apply mulch. Plow or shovel a shallow furrow along each row and roll the soil over the canes. In early April, use a pitchfork to lift the canes out of the soil. Put the soil used to cover the canes back into the furrow.”https://extension.colostate.edu/topic-areas/yard-garden/raspberries-for-the-home-garden-7-001/ You can use straw as your mulch, or you could even use a layer of plastic to keep the canes warmer in cold weather. Overhead Irrigation Strange as it may seem, overhead irrigation on cold nights can actually help to protect plants from frost. The reason is that heat is released as water freezes. If not done properly, this method can do more harm than good to your plants. This is more of a last-ditch effort if you know that your plants will not survive otherwise. You can learn more about this unconventional frost protection technique on the Penn State University website. Cold Hardy Raspberry Plants Choosing winter hardy raspberry plants is another great way to protect against cold and frost. Different varieties will survive in different USDA hardiness zones, but most can tolerate Zones 5 to 7 without any trouble. You can find your hardiness zone on this map from the USDA. Yellow raspberries are really just red raspberries without the red pigment. They can also be quite winter hardy! Here are some cold hardy raspberry varieties that are champions at withstanding winter frost. Anne - this fall bearing raspberry variety is cold hardy and produces large, firm, pale yellow berries. It grows best in USDA Hardiness Zones 4 to 7. You can learn more about Anne raspberries on the Nourse Farms website.Boyne – this summer bearing raspberry variety is cold hardy and produces medium-sized red berries. It grows best in USDA Hardiness Zones 3 to 7. You can learn more about Boyne raspberries on the Nourse Farms website.Bristol - this summer bearing raspberry variety is cold hardy as far as black raspberries go, but is not as winter hardy as its red raspberry cousins. It produces small black or deep purple berries that grow in clusters. It grows best in USDA Hardiness Zones 5 to 8. You can learn more about Bristol raspberries on the Nourse Farms website.Caroline - this fall bearing raspberry variety is cold hardy and produces medium to large red berries. It grows best in USDA Hardiness Zones 4 to 7. You can learn more about Caroline raspberries on the Nourse Farms website.Double Gold - this fall bearing raspberry variety is cold hardy and produces large pink and gold berries. It grows best in USDA Hardiness Zones 5 to 7. You can learn more about Double Gold raspberries on the Nourse Farms website.Encore - this summer bearing raspberry variety is cold hardy and produces large red berries. It grows best in USDA Hardiness Zones 4 to 7. You can learn more about Encore raspberries on the Nourse Farms website.Heritage - this fall bearing raspberry variety is cold hardy and produces medium to large red berries. It grows best in USDA Hardiness Zones 4 to 8. You can learn more about Heritage raspberries on the Nourse Farms website.Killarney - this summer bearing raspberry variety is cold hardy and produces medium-sized red berries. It grows best in USDA Hardiness Zones 4 to 7. You can learn more about Killarney raspberries on the Nourse Farms website.Latham - this summer bearing raspberry variety is cold hardy and produces medium-sized red berries. It grows best in USDA Hardiness Zones 3 to 8. You can learn more about Latham raspberries on the Nourse Farms website.Nova - this summer bearing raspberry variety is cold hardy and also tolerant of heat. It produces medium to large red berries. It grows best in USDA Hardiness Zones 3 to 8. You can learn more about Nova raspberries on the Nourse Farms website.Polana - this fall bearing raspberry variety is cold hardy and produces medium to large red berries. It grows best in USDA Hardiness Zones 3 to 8. You can learn more about Polana raspberries on the Nourse Farms website.Prelude - this summer bearing raspberry variety is cold hardy and produces medium to large red berries. It is the earliest ripening summer red raspberry, and it grows best in USDA Hardiness Zones 4 to 8. You can learn more about Prelude raspberries on the Nourse Farms website. What Do I Do With My Raspberry Plants in Winter? Before winter arrives, clean up any plant material around your raspberry plants. Then, put down a layer of mulch for cold protection. Wait until spring to do any pruning and tying of canes to supports (such as a trellis system). Use a lattice, an arbor, or a stake and wire trellis system to support your raspberry plants. You can learn more about raspberry plants (and how they spread) in my article here. Conclusion Now you know that raspberry plants can survive frost in the winter. You are also aware of some of the more cold-hardy varieties and how to provide a little extra cold protection for your plants. You can check out all kinds of cold protection resources on this page. You might also want to check out my article on all the different colors of raspberries that are available. I hope you found this article helpful. If so, please share it with someone who can use the information. If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here. Enjoy! ~Jonathon