iGrow Gardening: Starting sweet potato slips

Growing sweet potatoes in the upper Midwest’s cooler climate and shorter growing season is becoming a fun experiment for gardeners. Starting your own slips can get you a jump on the season with strong healthy plants.

There are two different ways to produce slips. One is to plant a sweet potato or two in a pot and use the slips that grow. The other is to put a sweet potato in a jar of water and let shoots grow. Each method has different instructions.

Growing slips from

a potted potato

Pick a healthy and firm medium-sized sweet potato from last year’s crop. Be sure there are no soft spots or breaks in the skin to prevent rotting. Plant it at least 4 inches deep in a pot filled with good quality loose textured potting soil. The deeper the potato is placed, up to 6 inches, the more roots the slips will have and will produce healthier plants. Position the potato on its side so that the slips will come from about the same depth. Provide warmth, at least 75 degrees, and keep the soil evenly moist. Covering the pot with plastic wrap will help keep the soil moist. It will take about 2-3 weeks to see leaves break the surface. Once the leaves are above the soil surface, place the container in a bright sunny window or under fluorescent lights. Shoots grown in low light will stretch out and be weak. You want short stocky stems with the leaves close together.

Once the slips are 6-8 inches long, you can “pull the slips”. Place one hand on the soil to hold the potato in place and give a sharp quick pull on one shoot at a time with your other hand. Each slip will have roots along its length. Sweet potatoes can produce multiple crops of slips. Leave the potato in place and another group of slips will develop. If it is too early to plant outside, the slips can be stored in a glass of water or planted individually in pots. See below for instructions.

Growing slips in

a jar of water

Again, pick healthy but smaller potatoes. Choose a container that will allow half of the potato to be submerged in the water. Next, look carefully at the potato. The end that was removed from the root last fall is considered the “top”. The end furthest from the where the potato joined the root is considered the “bottom”. Use three sturdy round toothpicks for each potato and insert them at equal distances around the middle of the potato. Put into the container with the bottom half in the water, using the toothpicks to support it halfway out of the water. Place in a bright sunny window sill. In about two weeks, shoots will emerge. Allow them to grow to around 8 inches long.

At this point, the shoots will not have roots. To develop roots, pull the shoots off the potato and put them in a glass of water 4-6 inches deep. Roots will form within a week and by the third week will be long enough for planting outdoors. Be sure to change water frequently to prevent fungus and mold from developing. Adding a drop or two of liquid fertilizer will provide all the nutrients needed for strong growth.

Keeping slips until

time to plant

Sweet potatoes are a tropical crop and not planted outside until the soil temperature is at least 50 degrees. Sometimes the weather does not cooperate and you need to delay putting your slips outside. To keep the slips healthy, either hold them in the water or pot them in flower pots. If holding them in water, continue changing it frequently and adding fertilizer every week. The slips will continue to grow and can be divided for more slips. Once slips are around 12 inches long, break off the end 6 inches and put them in water to root. This is one easy way to get more slips from a single potato. Slips can also be planted individually in a 6-inch pot with good quality potting soil. Plant as deeply as possible, water and fertilize with half-strength fertilizer weekly. Keep them in a sunny window or under lights.

When slips are planted in pots, they develop larger roots adapted for soil and will have a 2-3 week headstart on planting slips held in water.

Planting sweet potatoes

Once the soil is at least 50 degrees, sweet potatoes can be planted. Allow a large area for the vines to spread. Sweet potatoes will grow in many soil types including moderate clay. Looser more fertile soil will produce more potatoes. Plant slips or potted plants at the same depth as the water or potting soil. Space 12 inches apart for bakers and if you are trying to grow a super-size potato, plant at least 24 inches between plants. Leave 24 inches between the rows. Keep the soil evenly moist, fertilize along with your other garden plants. Straw mulch 4-6 inches deep will keep the soil moist and cover any root that may grow out of heavy soil.

Midseason, the vines may seem like monsters taking over the garden. Go ahead and prune them back. Removing 12-16 inches will not harm the plants and will keep them in line. If the weather conditions are right, the vines may bloom with morning-glory-type blooms. This is because sweet potatoes are morning glories. It is not necessary for the plants to bloom. They will make sweet potatoes automatically. For information on digging and storing sweet potatoes, refer to this iGrow article: http://igrow.org/gardens/gardening/sweet-potato-basics.