There are a number of ways to start sweet potato slips, some elaborate and expensive, others quite simple. The idea is to get the sweet potato to sprout and then planting those sprouts. The secret to healthy sweet potato plants is to start with slips from a healthy potato. Purchase these in small pots from garden centres or start your own slips with a good, disease-free sweet potato. Start the potato slips nine weeks before your soil warms to 15.6 degrees Celsius, in the spring.
Choose the right kind of sweet potato. Do not use those you find in the grocery store -- they may be treated to last longer and, thus, not sprout. Those from organic groceries or farmer's markets are ideal.
Push the sweet potato into the jar so that it stands vertically on the bottom. Pour water over it until the jar is half-full.
Set the jar in a warm area at least 26.7 degrees Celsius. Add more water as it evaporates so that the jar is always halfway filled with it. Every three days, pour out the water and add fresh water to the jar.
Prepare the garden soil by measuring the pH. Use a home testing meter or take advantage of the county cooperative extension's soil testing service. Sweet potatoes require a pH between 5.0 and 6.5.
Loosen the soil, removing any weeds, roots and other debris and crushing large clods of dirt. Add suggested amendments to raise or lower the soil's pH and mix them into the top 10 inches of the soil.
Mound up an 8-inch tall and wide ridge of soil. If you plant more than one row of sweet potato slips, allow 4 feet between rows.
Create holes for the slips, 12 to 18 inches apart, in the top of the ridge.
Snap the sweet potato slips from the tuber when the soil has warmed to 15.6 degrees Celsius. Size at this point varies, with some only a few inches and some substantially longer. Plant them deeply, with only the top foliage exposed above the soil.
Water the slips until the top 5 inches of soil are moist. Water to keep the soil moist for the first three days and then allow the soil to dry. Give the sweet potato plants 1 inch of water a week during periods of drought.
Fertilise the sweet potato plants when they begin to spread out. Dig a trench alongside the row, 6 inches away and 2 inches deep. Scatter 1 cup of bonemeal in the bottom of the trench and cover it with soil. Water the area to a depth of 10 inches to soak the bonemeal into the soil.