Most sweet potatoes are harvested during the week of the first frost, which varies by location. Typically, farmers located in cooler regions will harvest well before those who are located in warmer regions. Some sweet potatoes may start to poke through the ground before the first frost, and some farmers will pluck these early.
However, the longer you leave your sweet potatoes in the ground, the sweeter they will be! Another good rule is to harvest when tubers reach six to eight inches in length, as larger potatoes can become “woody.” Harvesting is best completed on a day with moderate to mild temperatures, when the air is warmer than 50 degrees Fahrenheit, so as to avoid chilling injury to the crops.
If your garden has been experiencing a time of drought, be sure to water your sweet potato rows immediately prior to harvest. This will irrigate the soil and prevent scratching of the delicate skin with hard chunks of dried out dirt. Some growers may have heard of a supposed toxin in frozen leaves which can seep into the roots of your plant if the plants are exposed to frost during this stage; this is not true. Sweet potato leaves are entirely edible. Furthermore, there is no harm in allowing exposure to a couple of light frosts provided that the days and soil remain warm. Still, when frost does come, do not wait. It is imperative to harvest your sweet potatoes within a couple of days.
While frost itself is not dangerous, cold temperatures have drastic effects on sweet potatoes. Once soil temperatures drop below 55 degrees Fahrenheit sweet potatoes can become subject to a permanent chilling injury called “hardcore.” When this occurs, the potatoes will remain hard regardless of how long they are cooked. Therefore, becoming useless and ruining the crop. Furthermore, if roots are exposed to cold without proper leaf cover, they will lose their ability to absorb water from the soil.
When ready to begin your harvest, start by removing the vines from your sweet potatoes. Only remove the vines from the plants to be harvested that day. If you have several days worth of harvest to complete, leave the vines intact on all of the plants that you will not be digging that day. They will provide protection until you can get to the rest of the crop.
Clip the vines and roll them, leaving gaps between the rows. You should leave stumps to show where to dig for your sweet potatoes. Rakes do not tend to be helpful at “grabbing” the vines, but digging forks can be useful.
Roots will often stick up out of the ground. Therefore, mowing or similarly, potato digging machines will do far too much damage to delicate sweet potatoes. Sweet potatoes need to be dug by hand, often with the assistance of digging forks. Using these forks, dig up the tuberous roots. The roots grow underground in the shape of a bunch of bananas. We advise you begin digging about a foot from the center of the plant so that you avoid damaging them.
To start, dig about six inches straight down. Then, turn at an angle towards the center of the plant, and very gently remove the sweet potatoes by hand. Be very careful not to drop or throw the sweet potatoes. In this stage, the roots are very sensitive to bruising. The sweet potato skin is also very fragile and any abrasions need to be avoided as well.
Place the potatoes on the ground beside where they have been grown so that it will be easy to identify the most productive plants. You will likely want to save a few of these sweet potatoes for making slips later.
Allow the sweet potatoes to dry in the sun for about an hour, provided the weather allows. Do not leave roots exposed to temperatures above 90 degrees Fahrenheit for more than 30 minutes, or you risk them being scalded by the sun. Conversely, if it is below 55 degrees, they will suffer from dangerous chilling.
If you decide you would like to grow your own slips for the next season, select the best seed potatoes from the most productive crops. These should be easy to determine if you laid your potatoes out according to the above recommendations. Place these potatoes aside, then grade the rest of your potatoes into ones to “use first” and ones to store.
Any potatoes with soft, wet, damaged areas or deep holes will not store and should be pulled for immediate home use or composting. Larger, open or broken surfaces will cure. Curing forms a second, tougher skin over this fragile outer layer and potatoes with these minor blemishes can be safely stored.
After laying in the sun for up to an hour, spread your sweet potatoes out and allow them to dry somewhere away from the sun that is at least 45 degrees Fahrenheit for a few hours. Remember, prior to this stage, we have not washed our sweet potatoes. You can shake off excess soil, but washing will encourage rot. You only want to wash your sweet potato immediately prior to cooking. It is still critical to handle the sweet potatoes very gently, as their delicate skin is still very susceptible to scratching and bruising.
As a note, the very small or damaged potatoes may not be exceptionally sweet, as they have not yet been cured. Some people compare the flavor as more similar to Irish Potatoes, so you may wish to use discretion when using them in recipes at this stage. The rest of the potatoes can be placed into baskets or cardboard boxes for further curing and storage.
Simple Curing Method
There are several methods for curing sweet potatoes. One method is to store the potatoes in a well-ventilated spot with a consistent temperature of 85 to 90 degrees Fahrenheit for ten to fifteen days. Ensure the potatoes are not touching one another. When the curing process is complete, check for any potatoes that still show signs of bruising and discard them.
After this, the sweet potatoes should be stored in a room around 55 to 60 degrees with a humidity of 75 to 80 percent. These sweet potatoes should keep for several months. Whenever you need a sweet potato, remember not to dig through the box or bin, as this may bruise and damage the sweet potatoes.
Using a Curing Chamber
Another method of curing sweet potatoes is to create a curing chamber in your home oven. First, place an open pan of water on the floor of your oven for humidity. Place a standard household or workshop light with a 40-watt incandescent light bulb on one of the shelves of the oven. This light is your heat source. Place a thermometer on the middle shelf where you will be able to read it through the oven’s window with the door closed. Close the oven door almost entirely. Our recommendations say to place a wooden ruler or similar flat object in the opening to provide just a crack of ventilation. Turn on the light. Leave the arrangement for approximately an hour, and then check the thermometer. You are aiming for a temperature between 80 and 85 degrees Fahrenheit. If the temperature is out of this range, change to a thicker or thinner spacer, accordingly.
Another method is to use a large picnic cooler and electric heating pad to create a curing chamber. Whatever your method, once your chamber is between 80 and 85 degrees, gently place the sweet potatoes inside, and close the door (remember your spacer!). Check the temperature twice a day, adjust as needed, and plan to leave the sweet potatoes for seven days.
Storing Your Potatoes
Sweet potatoes should be stored six to eight weeks in a cool environment (between 55 and 60 degrees Fahrenheit) with high humidity before cooking for the best flavor. In the south, some farmers choose to bury them outdoors in “clamps” (mounds of straw and soil) to save indoor space. Beware of storing anywhere with temperatures below 55 degrees as this can darken the flesh and alter the texture of the sweet potato. Similarly, sweet potatoes should never be stored in the refrigerator. Stored properly, cured sweet potatoes will last six to eight months.