Sweet potatoes have a way of bringing the warmth of the summer garden into fall when combined with aromatic spices like cinnamon, clove, and allspice. The recipe potential for sweet potatoes is almost endless. You can roast them in the oven with butter, salt, and pepper for a savory side, stir fry the leaves with garlic, bake them into a pie, and so on. Native to tropical regions of the Americas, these sweet, starchy root vegetables are teeming with protein, vitamins, fiber, and potassium, making them a nutrient-dense vegetable worth cultivating. All parts of the sweet potato are edible, unlike the standard potato. This is because sweet potatoes are not related to potatoes at all. They are in the same family as morning glories, Convolvulaceae.
These versatile root vegetables grow best in warm, wet climates, but they can thrive in most environments if you ensure the proper amounts of light, heat, and humidity. They grow vigorously as a vine, only rarely producing flowers. Since flowers are rare except in perfect conditions, sweet potatoes are not grown from seeds. Instead, they grow from slips. There are two ways to start slips; in soil and in water.
What are Sweet Potato Slips?
A “slip” is a rooted sprout that is produced from a mature sweet potato, a clone. Given the proper conditions, one sweet potato can produce anywhere from 5 to 12 slips, which equates to that many new plants. Each new plant has the potential to produce at least a pound of sweet potatoes. You can purchase sweet potato slips online, but they are quite expensive. Typically, you will pay about $10 for each slip. Fortunately, they are very simple to start at home and they don’t require much to get started. The best part? You can grow them from organic sweet potatoes you buy at the grocery store!
It’s very important to make sure your sweet potatoes are organic. Conventionally grown sweet potatoes are often chemically treated with chlorpropham, a root growth inhibitor. This is done to make sure the vegetables don’t start to sprout while they’re sitting on a store shelf, making them last longer on the shelf while looking more appealing to consumers. Obviously, this will be an issue if you try to sprout a conventional sweet potato, so stick with organic for this project.
Starting Slips in Soil
About 6-10 weeks before the appropriate planting date (depending on your area’s last frost date), start your slips. If you have a longer growing season, you can start closer to the 6 week out mark, but if your growing season is short, you may need to start closer to the 10 week mark. In addition to organic sweet potatoes, you’ll need a few other things:
A tub or container that allows about 1” of space below each sweet potato
Soil medium (This can be store bought soil, sawdust, or a mixture of these. It needs to be a well-draining medium.)
A warm, dark place to keep them until they sprout
Eventually, you’ll need clear jars or cups to root the slips
Step 1: Add soil medium to the tub
Your soil medium can consist of potting mix, raised bed mix, sand, or even sawdust. As a note, if you opt for sand or sawdust, those mediums will absorb water very quickly, meaning you’ll need to water your slips frequently. The sweet potato itself holds within it all the nutrients the slips will need, so don’t add any fertilizer to the soil. Your tub needs to be deep enough to cover about ⅔ of each sweet potato lying on its side with about an inch of space underneath. Pour about an inch of soil into the tub.
Step 2: Add the sweet potatoes
Set the sweet potatoes on top of that inch of soil. They need to be on their sides because one end will grow sprouts that will become vines and leaves, while the other end will grow the roots. Until the sweet potatoes begin to sprout, it is likely that you will not know which end is which. If you bury the sprouting end, it won’t sprout. Likewise, if the root end is bottom-up, it won’t grow roots. The potato lying on its side gives either end the opportunity to sprout. When laying out your sweet potatoes, don’t be afraid to put them close together. They can stand to be a little crowded, just do not stack them.
Step 3: Cover with Soil Medium & Set Aside
Now that your sweet potatoes are lying on top of the inch of soil, you need to cover them about ¾ of the way with soil. Water them so that the soil is moist but not sopping wet. For the next couple of weeks, you’ll be engaged in a delicate dance of making sure the soil stays in this balance. If they stay too wet, they are vulnerable to rot. If they dry out, they will not sprout slips. Cover the tub so that they are not exposed to light, watering and checking on them daily. During this time, they need to be kept at a temperature of about 75 degrees or warmer. After about 6 to 8 days, sprouts should be visible.
Step 4: Rooting the Sprouts & Transplanting the Slips
When the sprouts are at least 3 inches long, they are ready to be separated from the sweet potato and rooted in water. First, detach the sprout from the sweet potato by carefully twisting it off with your fingers. Do this for all sprouts then, place them in a glass jar or clear cup, submerging the bottom part of the slip in the water. Make sure the leaves are not submerged and are sticking out the top of the cup or jar.
This process is the same as if you were propagating any plant from a cutting in water. Set these jars in a sunny windowsill. In a matter of days, white, translucent roots will become visible. The rooted slips are ready to be transplanted into the soil when the roots are at least 3 inches long, which could take a couple of weeks. To give them the best start, you should let the plants mature for 2-3 more weeks by potting them up in soil before moving them outdoors to their garden bed homes.
Step 5: Potting the Slips
Now it’s time to transfer your slips to a pot with soil. A small 4” pot and potting mix will do fine, it doesn’t have to be anything fancy. If your plant shows signs of a struggle such as yellowing leaves, consider adding a small amount of compost to the soil and make sure it’s getting plenty of sun and warmth. When the soil is consistently above 50 degrees and there isn’t the slightest hint of a chill in the air, your slips are ready to be transplanted outdoors.
Step 6: Planting Slips Outdoors
Transplant the slips into soil (ideally warm, sandy, loamy soil). Dig a hole just larger than the length and width of the roots, keeping all the foliage above the soil. Be sure to space each sweet potato plant at least 12 inches apart, giving them plenty of space to grow lots of sweet potatoes below the surface. Sweet potato is a vining plant and will grow to take up a lot of space. If you don’t feel you have room for them, you can give them a trellis to climb.
Starting Slips in Water vs. Soil
Another way to start sweet potato slips is to utilize the water method. You need to be able to identify the rooting end and the sprouting end if you choose to use the water method. This can be done by judging the size of the ends and the number of eyes. The sprouting end may be slightly larger and have more eyes than the rooting end, and the end that tapers is usually to rooting end. As a caution, the water method takes a couple of weeks longer and presents a bit more of a challenge in my experience and research.
All you need to do is submerge a sweet potato, rooting side down, halfway into a glass jar of water. Use toothpicks to hold it halfway out of the water (like in the photo above) and set it in a sunny windowsill. Change the water frequently to prevent root rot, as leaving the potato in stagnant water is a sure way to render it unviable. In about 8 to 10 weeks, your slips should have roots and you can pot them up and transplant them outdoors as if you were using the soil method.
From Slips to Harvest
Sweet potatoes will enjoy a warm, wet summer and are very intolerant of frost. They are a tropical plant after all. Keep this in mind when determining the right time to start slips. Once in the garden, they will need at least six hours of sunlight each day and take 90 to 120 days to reach full maturity. Similarly to standard potatoes, sweet potato leaves will begin to yellow and wither when they are ready to harvest. When they’re ready, dig them up and leave them to cure in a warm, humid environment for a couple of weeks. After that, they can be stored in a cool, dry place for up to several months.
At the end of the slip-making process, you might end up with more slips than you’re willing or able to plant. Share them with friends, family, and neighbors if you can! This is my first informed attempt at growing sweet potatoes, so stay tuned for updates on our sweet potato plants and other garden and farm updates. Let me know in the comments what you’re starting to grow now, if anything. I love hearing from you all.
Cheers,
Allyson