dormancy for sprouting potatoes

You can store potatoes for a long time, but they will eventually start to sprout. However, if you know what makes them sprout, you can take steps to slow down the process and increase storage time. So, why do potatoes sprout? Potatoes sprout to produce a new plant. Enzymes in the potato convert starch into sugar. This sugar provides energy for sprouts to grow from the eyes (buds) of the potato. If you plant a potato, the sprouts grow toward the soil surface and produce leaves to create energy by photosynthesis. Of course, some potatoes that you buy at the store are treated with sprout inhibitors, so it will take longer for those ones to sprout. In this article, we’ll take a closer look at why potatoes sprout. We’ll also talk about how to prevent sprouting (or how to speed it up if you want sprouted potatoes for planting!) Let’s begin. Why Do Potatoes Sprout? Potatoes sprout as a natural part of their reproductive cycle. Sprouting is one of the early steps in the creation of a new potato plant. A potato will sprout as a natural part of its reproductive cycle. After a period of dormancy, potato tubers prepare to sprout. (This is encouraged by specific environmental conditions for light, temperature, and humidity – more on this later). First, an enzyme in potatoes turns some of the starches into sugar. Storage temperature has an effect on how this process plays out The sugar is now more readily available as energy for the formation of new sprouts. These sprouts grow from the eyes (or buds) on potato plants. The eyes on a potato will look like small white indents before they begin to sprout. At first, the eyes are tiny, but after sprouting occurs, you can see the sprouts as they grow longer. If not planted, the sprouts will grow and use up energy (sugar or starches) from the potato tuber until it is exhausted. You can see the potato plant become wrinkled as this happens over time. Eventually, it will have a “deflated” appearance. These potatoes are starting to get a little wrinkled, since they have used up some of their starches to grow bigger sprouts. However, if you plant a sprouted potato (or a piece of potato with a sprouted eye) about 4 to 6 inches deep, it will grow up towards the surface of the soil. Eventually, the sprouts will break the soil surface and produce tall stems and leaves to produce energy from sunlight by photosynthesis. The plant will store this energy in new underground tubers, thus producing more potatoes and making way for the cycle to start again. What Causes Potatoes To Sprout? There are several factors that cause potatoes to sprout, including: TemperatureHumidityLightDormancy (rest period) Let’s start with temperature. Temperature For Sprouting Potatoes In general cooler temperatures are better for storing potatoes if you want to prevent them from sprouting. Of course, you don’t want them to get too cold: frost or freezing temperatures (below 32 degrees Fahrenheit) will damage the tubers. Frost or freezing temperatures will damage potato plants and tubers. The University of Maine suggests storing seed potatoes at 38 degrees Fahrenheit (3 degrees Celsius) to prevent sprouting. If you want to grow new plants, warm up the seed potatoes to room temperature, or about 70 degrees Fahrenheit (21 degrees Celsius). Do this about 2 weeks before planting (5 weeks before last spring frost). (You can find the last spring frost date in your area on this page from the Old Farmer’s Almanac.) Warming up the seed potatoes for a couple of weeks will encourage them to start sprouting (they will think spring has arrived!) If the sprouts become too long, you can always put the potatoes back in cool storage until it is time to plant them. If you don’t have such a cool place to keep potatoes, the University of Maryland suggests a temperature of 40 to 50 degrees Fahrenheit (4 to 10 degrees Celsius) for long-term storage. Higher temperatures will cause problems, such as early sprouting or rotten tubers. In fact, the Oregon State University suggests that potatoes will shrivel up much faster when storage temperatures are above 50 degrees Fahrenheit (10 degrees Celsius). This is due to early sprouting and depletion of energy reserves (the starches inside the potato are “sucked out” to grow the sprouts on the outside!) On the other hand, if you want to cause potatoes to sprout before planting (“green sprouting”), the ideal temperature is 70 degrees Fahrenheit (21 degrees Celsius) with high humidity. Lay potatoes out in a warm, bright area to encourage rapid sprouting before you plant. The table below summarizes the temperature ranges for preventing or encouraging potato plants to sprout. TemperatureRangeDescriptionbelow32F(0C)Frost orfreezing candamage a tuber.38F(3C)Ideal for long-termstorage topreventsprouting.40-50F(4-10C)This temp will delaysprouting.51-69F(10-21C)A potatosprouts alittle faster at this temp.70F(21C)Ideal tempif you want to sproutpotatoes fast.This table summarizes the temperature ranges for preventing or encouraging potato plants to sprout. Humidity For Sprouting Potatoes You might think that storing potatoes in a dry place would work well, but there is a problem. Potatoes will dry out and wither when stored in a place with low humidity. Instead, the University of Maryland Extension suggests storing potatoes in conditions with 90% relative humidity, at 40 to 50 degrees Fahrenheit (4 to 10 degrees Celsius) where they can keep for 6 to 8 months. Keeping the potatoes in bags or boxes with ventilation will prevent them from rotting, sprouting, or turning green in the light. The University of Idaho Extension echoes this suggestion, and they recommend a relative humidity of 90% to 95% for long-term storage of potato tubers. A root cellar is a cool place to story potatoes. It is very difficult to maintain such high humidity levels in your home. However, you can use a perforated plastic bag (one with holes that is not totally sealed) to increase the humidity levels for stored potatoes while still giving them air circulation. Light For Sprouting Potatoes Potatoes do not need light to sprout. Think about it: if you plant a potato tuber before it has sprouted, it can still sprout and grow into a full-fledged plant. In fact, the University of Maryland suggests that exposing potato tubers to light will help to keep the sprouts short. This may be useful if they start to sprout earlier than you expected. However, you should not store potatoes in sunlight if you plan to eat them rather than sprouting them. When potatoes are exposed to sunlight, they will turn green (due to chlorophyll). Potatoes produce chlorophyll and turn green in sunlight.Image courtesy of user:Rasbak via:Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Groene_aardappels_%27Dor%C3%A9%27_(Solanum_tuberosum_%27Dor%C3%A9%27).jpg (You can learn more about why potatoes turn green (and how to prevent it) in my article here.) In addition to producing chlorophyll, potatoes left out in sunlight will also produce solanine. Solanine is a toxic substance that can make you sick if you eat enough of it. Interestingly enough, potatoes do not need soil in order to sprout! They also don’t need to be buried right away. You can put them on the surface of the soil and they will still sprout. You can “hill” them with soil, mulch, or straw to prevent green potatoes. Hilling potato plants will prevent sun exposure and green tubers. (Hilling just means piling up soil around the base of potato plants – you can learn more about when and how to do it in my article here). So, if your potatoes turn green, cut away the green parts, plant them if they sprout, or get rid of them entirely! Dormancy For Sprouting Potatoes In addition to temperature, humidity, and light, potatoes also have a requirement for a “rest period” before they will sprout. A potato tuber needs this rest period to break dormancy before it will sprout and grow into new plant. According to the Texas A&M University Extension, cool temperatures or very warm temperatures can both break the dormancy period for potatoes. Russet potatoes have a long dormancy period, often 4 to 5 months or longer at cool temperatures. Cool temperatures mimic what underground potato tubers would experience during winter, while warm temperatures would tell them that spring or summer has arrived. Either way, the potatoes are programmed to start sprouting after one of these signals that it is time to break dormancy. How To Make Potatoes Sprout Faster If you want to make potatoes sprout faster to prepare for planting, here’s how to do it: Temperature – keep potatoes warm to encourage sprouting. Temperatures above 50 degrees Fahrenheit (10 degrees Celsius) will work, but 70 degrees Fahrenheit (21 degrees Celsius) is ideal.Humidity/Moisture – keep potatoes at high humidity to prevent them from drying out. A relative humidity of 90% to 95% is recommended.Light – you don’t need light to sprout potatoes. In fact, exposing the sprouts to light after they start to grow can slow them down. So, keep potatoes in the dark until the sprouts are established.Dormancy – according to the University of Idaho Extension, most potatoes will naturally sprout 30 to 140 days after harvest. Length of dormancy depends largely on the potato variety. However, all potatoes need a dormancy period before they will sprout, regardless of the other factors above. Sprouting potatoes for planting is also known as “chitting”, and it helps you to weed out tubers that have little or no potential for good growth. By only planting tubers that sprout well, you increase the chance that each potato will grow into a healthy plant that will produce a generous yield. Planting potatoes that have already sprouted increases the chances that they will thrive. In addition, you can use green sprouting (also called pipping) to encourage potatoes to sprout early. According to the University of Maine Extension, you should start by spreading out the potatoes in a layer in an area exposed to light (it’s ok if the potatoes turn green, since you will be planting them instead of eating them). The best temperature to green sprout potatoes is 70 degrees Fahrenheit (21 degrees Celsius). You can turn them over to make the sprouting more uniform. Green sprouting gives you fast-emerging short sprouts, which will start producing tubers early in the season. One more thing to remember about sprouting potatoes: it might be more difficult with tubers from the grocery store. The reason is that many commercially grown potatoes are treated with a chemical called clorproham. Clorproham is a sprout inhibitor and herbicide applied to potatoes. It prevents them from sprouting during storage, transport, and display at grocery stores. This is good for grocery stores and consumers, but it is bad if you want to sprout potatoes for planting in your garden! Washing may help, but if potatoes stay too wet for too long, they might rot instead of sprouting. If you want to avoid this problem, use certified seed potatoes intended for planting only. These have not been treated with sprout inhibitor. You can buy seed potatoes online from a reputable seed company like Gurney’s. You can also find seed potatoes seasonally at brick and mortar gardening stores near you. How To Prevent Potatoes From Sprouting On the other hand, you might want to prevent potatoes from sprouting if: you want to store them for eating, orit isn’t quite time to plant yet Either way, here’s how to stop potatoes from sprouting: Temperature – keep potatoes cool to prevent sprouting. Temperatures between 40 and 50 degrees Fahrenheit (4 to 10 degrees Celsius) will work, but 38 degrees Fahrenheit (3 degrees Celsius) is ideal.Humidity/Moisture – keep potatoes at high humidity to prevent them from drying out. A relative humidity of 90% to 95% is recommended.Light – you don’t need light to sprout potatoes. Exposure to sunlight will make potatoes turn green, so keep them in a dark place if you are storing them for eating.Dormancy – choose potato varieties with a longer dormancy period to prevent sprouting. You might have to experiment, but the University of Idaho suggests that Alpine Russet and Russet Burbank potatoes have the longest dormancy period, followed by Classic Russet and Umatilla Russet. If your potatoes sprout despite your best efforts to prevent it, don’t worry. You still have some options! What To Do With Sprouted Potatoes If you want to eat a sprouted potato and it isn’t wrinkled or green, you can cut out the eyes and process it as usual. Peel it if you like, cut away any green skin or flesh, and then cook it by boiling or baking. Of course, if you don’t want to eat a sprouted potato, you can always plant it. Can I Plant A Potato That Has Sprouted? You can plant a potato that has sprouted and it will grow into a new plant. You can do this in two ways: Plant the whole sprouted potato – this method has some advantages. You won’t have to wait for cut potato pieces to “cure” before planting. There will also be more energy for sprouts to grow early in the season, and you will often get larger, more vigorous plants.Cut the potato into pieces – this method allows you to get more potato plants from each sprouted potato. Just make sure that there is at least one sprouted eye per piece after you finish cutting. Don’t make the pieces too small, or they won’t have enough energy to reach the surface of the soil and start growing. According to the Texas A&M University Extension, the potato plant will be weak if it grows from a potato piece that was too small. The reason is that it won’t have enough energy (from starches and sugars) early in its life to get a good start on growth. If you plant a sprouted potato, a new plant will soon emerge from the soil. If you want to learn more, read my article for in-depth information on planting sprouted potatoes. Conclusion Now you know why potatoes sprout and how it happens. You also know how to prevent it to store potatoes longer (or how to speed it up to get sprouted potatoes for planting). If you don't have much space for growing potatoes, check out my article on how to grow potatoes in a bucket. You might also want to read my article on growing store bought potatoes (and what to look out for). 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