The next method we can use is the container method. This method is much faster and you can get a lot of slips from a pretty small space. But, you’re going to need some artificial lighting for this and, ideally, a seedling heat mat plus a place you don’t mind having a tub full of soil and potatoes sitting for a six to eight weeks.
For this method you’ll need a shallow container, potting soil or seed starting mix, a seedling heat mat, and some artificial lighting.
For sprouting just a few sweet potatoes the container you use can be something like a foil baking pan or a deep seedling tray. Really, any shallow container that can have drainage holes but that can also have something placed beneath it to catch water will work. The size is really up to you and how many sweet potatoes you want to sprout and how much room you have to do it.
Create drainage holes in the bottom of your container and put a layer of potting soil or seed starting mix into the container about two inches deep. Nestle your sweet potatoes into the soil, laying them flat, and then fill in with more soil around the potatoes until they’re covered at least halfway up. The reason we do it this way instead of completely burying them is to prevent the potatoes from rotting before they get a chance to root and sprout. You may also choose to completely cover them very lightly with the potting soil. Put your container on top of something to catch the water, so the lid to the baking sheet if that’s what your using or another larger container if you’re using something else, and then water the soil thoroughly. We don’t want it sopping wet, but you’ll want to keep the soil moist as the roots begin to form. Put the container on top of the heat mat if you have one, which I highly recommend because it definitely makes this process go faster. The sooner you can get the sweet potato to form roots the lower the chances that you’ll have any of the tubers begin to rot. With heat, it should take about a week for the roots to form and then about another week or so to start seeing sprouts. Much faster than the water method. At this point be sure you give the sprouts some light, similar to growing seedlings indoors. Let them get to be about six inches tall before removing for planting.
Image: Zac Hoppenstedt, KSU
Our final method for sprouting sweet potato slips is similar to the container method and that’s the in-ground method. We’ll be doing this out in our garden area, so the effectiveness of this method is going to depend on how warm your soil can get in the spring.
For sprouting sweet potatoes outdoors, we want the soil temperature to be at least 65F or 18C. If your soil isn’t warm enough on its own or waiting for it to warm up naturally won’t give you enough time to get the slips sprouted before it’s time to actually plant, you can use mini greenhouses, milk jugs, hoops with greenhouse plastic or black plastic mulch or tarps to warm the soil more quickly. You’ll need to maintain this soil temperature to successfully sprout and grow your slips, so be sure it’s something that can be maintained while also allowing for sunlight on the sprouts.
Make sure your soil is loosened and well-watered prior to planting your tubers. You can either bury just the rooting end of the sweet potato in the soil and leave the top sprouting half outside the soil similarly to how we did it with the water method or you can lay them flat like we did with the indoor method and cover them lightly with soil. Once again we’re going to keep the soil moist while we wait for the roots to form and the sprouts to pop up so the warmer the soil is to start with and the warmer we keep it, the less likely we are to have any of the potatoes rot before they sprout.
And, just like with the indoor method, how long it takes for the roots to start forming will be based on the level of moisture and warmth. This could be as quickly as a week or it could take a couple weeks if your soil is cool or you allow it to dry out to frequently. After the roots start to form, it should only be another week or two before you start to see those shoots popping up. Now, because these are outside and you’ll have natural sunlight on them, the shoots will likely grow quickly to get to that six-inch height we want for our slips.
Which Method Should You Choose?
Whichever method you choose will be based on what’s convenient for you, but may also be partially determined by how long you have before it’s the ideal time to plant your slips. You want to wait at least a month after your last frost in spring, when the soil temperature is at least 65F or 18C and when the nighttime air temperatures are consistently above 60 F or 15.5 C. So, in some cases the in-ground method won’t be possible because ground temps won’t be warm enough. And if you’re only sprouting two or three potatoes, the water method may be most convenient.
Get creative if you need to! Experiment and find what works for you. Try all three methods at the same time, even, and decide from there.
No matter which method you use, once your sprouts get around six-inches tall, it’s time to remove them from the sweet potato and use them as slips.
Preparing Your Slips
To remove the slips from the potato, carefully twist or cut them from the tuber. If little roots have formed where the sprout meets the tuber, try to keep those intact.
Remove the lower leaves from the spouts and at this point you have two options. The first is to put the bottoms of the slips in a jar of water for a few days to pull visible roots before planting. If you’re new to growing sweet potatoes or you have soil that isn’t very loose or loamy, this method ensures your new slips take root more quickly because of the actively growing roots.
But, if you’re an experienced sweet potato grower and your soil is conducive, you can just plant those newly harvested slips right into the prepared bed. Bury the slips all the way up to the top leaves and keep them evenly moist to promote those roots to grow in the soil.
No matter which you choose, your slips should be planted about 12 inches apart from each other and the stem should be about 4 inches into your 8-inch deep mound.
Your friend in the garden,
References and Resources
Ep. 94 - Growing Sweet Potatoes
Growing Sweet Potatoes in Missouri | MU Extension
Sweet Potato Starts and Plantings (k-state.edu)