Start off with a firm sweet potato from the grocery store. If it has little buds already, great! The potato will grow even faster. I like to start off by asking students if they think the potato is alive (it is). Then I would ask what part of the plant students think the potato comes from (it’s part of the root). Stress to students that this is NOT a seed, but instead we are going to grow a whole new plant from just a part of the root of the plant.
Decide which side of the potato is more tapered. This side will go DOWN, and the rounder side will face upwards. Place toothpicks into the sweet potato around the middle. Place potato into a jar filled with water so that the toothpicks rest on top of the jar, holding it up. About half of the potato should be covered by water. Place jar in a window with a lot of sun, or near a heater (a little heat speeds up growth). Add water when necessary and completely change the water at least once a week. Now make observations and predictions, and wait! Roots will start to grow in just a few days, and then shoots of leaves. The plant is really quite beautiful, with purple stems and bright green leaves. After three weeks or so, you can take out the toothpicks and bury the potato in dirt for a great classroom plant.
If, however, you plan to plant it outside, be aware that it requires a long, warm growing season to produce any harvest (you need between 3-5 months without any frost). They grow best in well-drained soil (if your soil has too much clay, consider a raised bed). Vines will grow lushly, but they will take root where ever they touch the soil. Avoid this, as runners will cause the harvest to be smaller. You may want to place a couple of old tires around the plant to help keep the vines off the ground.
You will know that the plant is ready to harvest because the leaves begin to turn yellow and die back. Prepare the plant for harvest by cutting the vines back about 2-3 days before harvest (this toughens the skin of the potatoes and improves their texture). Once they are harvested, you may want to cure the potatoes in order to increase their sweetness and brighten the color of the flesh. Cure them by placing them in a warm (85 degrees is best) and humid space for about 5 days. After 5 days, they are ready to be eaten!
- Sweet Potato Slips: How to Grow Your Own Sweet Potatoes from Scratch (green-talk.com)