How to Grow Your Own Sweet Potato Slips

Sweet potatoes are not usually planted the same way as are white potatoes. If a whole sweet potato is placed in the ground in early spring —  when white potatoes are usually planted —  the cold weather will inhibit its growth and it might rot. For this reason, the recommended propagation technique for sweet potatoes is to plant “slips” after the last frost date. Slips are the rooted sprouts that grow out of the sweet potato tuber. They can be purchased from a reputable seed company, or you can grow them yourself, which is much more fun! It also works as an interesting and engaging garden activity for children.

One potato tuber will often produce more than a handful of sprouts or slips. These slips are removed from the original tuber by a careful twist, or, by keeping them attached to the tuber and slicing them off.  Each of those slips can grow into a plant that can produce about 6 sweet potatoes. It generally will take about 6 weeks for the sprouts to be ready to slip off the tubers. Planting time in Central Virginia is after the last frost date (I plant in the third week of May to be safe). That means that the slips should be started the first week in April, so they’ll be ready to plant in the garden in the third week of May.  

 

To begin the process, have these materials available:

• organic ( if possible) sweet potatoes; whether store bought or purchased as “seed” potatoes from a seed company
• a strong knife to slice each tuber in half
• a cutting board or piece of wood ( my photo shows a section of 2 by 4 that just happenend to be in our greenhouse!)
• at least one aluminum baking tray with a cover ( I buy them at a grocery store in the baking section)
•  organic seed starter mix that you have pre-moistened ; enough to fill the tray and cover the potatoes

For the past 10 years, I have been using the following procedures to grow Japanese sweet potato slips. But any kind of sweet potato can be used. We grow the Japanese variety only because we love the less sweet flavor, and the drier texture.  During the first week of April:

1. Fill a tray with a moistened organic growing medium
2. Place a potato on a cutting board and slice lengthwise in half
3. Position each half with the cut side down on the planting medium
4. Push the potato into the mixture and cover with a little more of the mix
5. Cover the tray with a plastic top in a way that allows for some air circulation
6. Keep the tray under grow lights or florescent shop lights and do not let the soil dry out
7. You can also place the tray by a sunny window
8. To speed up the process, you can place the tray on a heating mat for plants. This is an optional step

After 2-3 weeks, you will begin to see reddish sprouts emerging from the sides and the tops of the tubers.  At this time, you can remove the plastic cover and continue to keep the tray of sprouting tubers moist. Soon, these stiff sprouts will begin to leaf out and grow roots. The roots will be attached to the seed potato.

The sprouts will continue growing roots underneath the sliced tuber. When there are several green leaves and some roots attached to each sprout, they are ready to be “slipped” off the tuber. This can be accomplished with a twist of the sprout. I prefer to slice the potato, in between the sprouts. Using this method, each sprout and some root will be attched to a small piece of potato. I do this because if I try to pull or “slip” it off the potato, sometimes it breaks. That is also a good reason to plan on having some extra by using one more seed potato than you think you need.

Now that the slips are off the potato, if the last frost date has passed, they can be planted into the previously prepared garden bed. Otherwise, they can be planted in small pots, and kept indoors under grow lights until after the last frost date passes.

I like to grow the slips in pots for about 2 weeks, even if the last frost date has passed. This extra step gives the slips a chance to develop larger leaves and a stronger root system. It takes a bit more time and energy but using this method, I have never lost a single plant in the row.

Determine how many slips and potatoes are needed.

I have always  been able to count on at least 6 healthy slips from each tuber. Oftentimes, there will be more. Each of those slips will mature into a plant that produces, on average, 6 tubers. And each plant is spaced about a foot apart in the garden. So if I want to be sure I will harvest a certain number of potatoes, some simple math is helpful.

I like to consume 2 potatoes per week : 2 times 52 weeks equals 104 tubers.

— 104 divided by 6 potatoes from each plant equals 18 plants, rounded up. I will need 18 slips.

–18 slips divided by 6 slips per seed potato equals 3 seed potatoes ( remember they are sliced in half to grow the slips).

Determine the  amount of space needed

I choose an area in my garden where the vines will be free to extend at least 4 feet from the main plant in every direction. This is because of the extensive vining habit of sweet potato plants. Since the correct plant spacing in the garden is 1 foot between plants, I will need an 18-foot row, or 2 or 3 smaller rows.

Below is a photo of the slips that have been growing in small pots. They are all lined up and ready to be transplanted into my row. One year, we had squirrels burrowing into the row, nibbling on all the potatoes!  Ever since then, we cover the row with black landscape fabric, which lets in the water and keeps out the squirrels. It also prevents weeds from growing in between the vines.

As the vines begin to grow, the soil will soon be blanketed by them.  The vines will “take over ” a wide space, growing 3 -4 feet in every direction! It’s a good idea to place an 18-inch stake in the ground in front or behind each plant. If you don’t mark each spot, as the vines grow, it becomes difficult to know exactly where to water. Placing the stakes also helps to identify the location of each plant later in the fall, when all the vines have to be cut off the plants.

Prepare the area for harvesting

After growing in the ground from mid-May until mid-October —  definitely before the first frost — it will be time to prepare the area for harvest. Because of the thick tangle of vines, we follow these steps; making the entire process quite easy and enjoyable.

1. Starting about a foot away from each rooted plant, cut away the vines. We use a garden shear.

2. Pull them to the sides of the row so you can easily access the tubers.

3. Whatever bit of vine remains attached to the tops of the plants can now be cut away.

 

  Begin harvesting

With a trowel, gently dig around the plant in a wide circle, taking care not to cut into any potatoes. I scrape some soil away from the main plant as I also tug on the remaining stalks. In a few minutes, there they are! You’ve been waiting all season and at long last, they are ready. They grow as a cluster, attached to the main stem of the plant. With your trowel, lift them out one by one, or, if your soil is loose, you can pull on the main stalk and they will come out of the ground, all at once, still connected.

 

At this point, the potato skins are easily scratched. To harden the skins, leave the potatoes in the row for a few hours to begin to dry.  The next step is to gently rub off the soil, and it is best to do this with a soft cloth or with your hands.

 

Cure the potatoes for winter storage.

If the potateos are not properly cured, they will become soft before you can eat all of them! Sweet potatoes cure best in a constant temperature between 75° and 80° for about 10 days. One way to acheive this is to place the potatoes on a table in a room with an electric heater. After this curing period is over, they can remain in a basement or other room that maintains a temperature of about 60° – 65°F.

Now you can enjoy your harvest!

 

 

 

 

Helpful resources for all aspects of growing sweet potatoes:

https://extension.umd.edu/resource/growing-sweet-potatoes-home-garden

https://piedmontmastergardeners.org › article › sweet-p…