A potato plant will grow in most soils as long as it has been well dug. The soil should be clear of large lumps and stones. Add as much compost as is available, or bonemeal (or similar) at the time of digging. It is a good idea to prepare the soil in mid November or December to allow it to settle before planting and let the compost begin to break down. Although not fussy about the soil type, the potato prefers a slightly acidic soil, so do not add lime before, during or after planting.

The detail instructions are as follows:
Compare the size of your sweet potato to the size of your jar to make sure your jar is large enough.

Push three or four toothpicks into the side of the sweet potato. The toothpicks should be forming a circle around the middle of the sweet potato.

Place one end of the sweet potato down into the jar. The toothpicks should be long enough to cover the edge of the jar holding the upper half of the sweet potato out of the jar.

Fill the jar with water until the bottom half of the sweet potato is almost covered by the water.

Place the jar in a window so that it can have access to sunlight as it is now a growing plant. In about two to three weeks you will notice that the little potato buds have formed roots down into the water. Be sure to keep adequate water in the jar to promote the growth of the plant.

Watch for the green leaves to start sprouting from the top of the potato. It will really start to grow pretty fast by this time. The leaves will resemble a vine.

Replant your new sweet potato plant or vine into a pot or hanging basket when the leaves and roots have really taken off. Tend to your new sweet potato plant as you would any other green plant. You can also just keep the sweet potato in the jar and enjoy watching how long all the vines of the plant become.