Growing sweet potatoes is an easy and rewarding part of vegetable gardening, but before you can dig the soil and find large, delicious sweet potatoes, you'll need transplants. You can start transplants, also called slips, indoors 12 weeks before you plan to plant them outdoors. To grow sweet potato slips you don't need a lot of supplies or know-how, but you do need time, so planning ahead and getting started is crucial to having slips ready for transplant when outdoor temperatures are right for sweet potato planting.
Select sweet potatoes from your grocery store, farmer's market, or from last year's crop and wash them gently, checking for any mold or rotting spots. One potato could potentially make up to 50 slips, so know how much space you have in your garden before you purchase more than one or two.
Cut your potatoes in half or into large quarter sections with large skin sections available. Suspend your cut sections over the mouth of the jar by pushing toothpicks halfway into the potato to act as support props along the rim so a portion of the potato is in the jar and a portion of it extends out of the jar.
Fill the jar with enough water to submerge a third to half of the potato underwater. Place the jar in a sunny and warm window and leave it there, refilling the water as needed, and allow leafy sprouts to appear after a few weeks.
Wait until the sprouts have grown to about six inches tall before removing the potato from the water. Gently twist off the sprouts to separate them from the potato. Discard the potato once all the sprouts have been pulled off.
Prop the sprouts in a shallow bowl with the leaves extending over and beyond the rim, and the base of the sprouts resting along the bottom of the bowl. Fill the bowl with water so half of the sprout body is underwater.
Look for roots to appear within a few days, and continue to add more water as needed. Let the roots continue to grow until they are at least an inch long before planting the slips in loose, warm soil outdoors.