An easy way to start plants, also called slips, for growing yams in your vegetable garden is to first grow yams in water. To guarantee success with your yams in water, you'll need to start 12 weeks ahead of the planting time for your region before transplanting yams into the garden. Luckily, other than the time that it takes to grow the slips, it takes barely any effort to get the yams started and keep the water levels up.
Choose a yam that is narrow rather than fat and 4 to 6 inches long from a farmer's market, farmer's supply store, or local grocery. Buy yams that haven't been treated to prevent sprouting. The yams you use for growing in water need to be free of dents, gouges, scratches or rotted areas.
Slice the yam in half widthwise with one clean cut across the body of the yam. Hold a yam half over the opening of one of your jars to make sure it will fit though the hole.
Lower the yam into the hole with the cut surface facing down by about an inch. Space out three or more toothpicks around the yam and stick them halfway into the yam to hold it in place along the rim of the jar. Fill your jar with water all the way to the top so that a third of your yam half is underwater. Repeat this step with the other half of your yam and the second jar.
Set your jars in a warm, sunny window where they can sit undisturbed for four to eight weeks. Refill any water as needed to keep the cut ends of the yams submerged. Sprouts should begin to grow after three to four weeks.
Take the yam out of the water and twist off the sprouts once they are 6 inches tall. Set the sprouts in a bowl full of shallow water about 2 inches deep with the leafy tops sticking up out of the water.
Wait two to three weeks as roots form, refilling the water when needed, and transplant the slips outdoors once the roots are 1 inch long. Be sure to set the yams in full sun and keep the plantlets well moist for the first two to three weeks as it grows.