When I planted potatoes while WWOOFing in Japan we cut them in halves or quarters so that each piece had at least one eye. We covered the cut part of each piece with ashes and boxed them to take out to the field. We simply planted them that way about 8-12 inches apart and 6-8 inches deep. We also tended some potatoes planted earlier and the advice I got was to leave many stalks if you want small potatoes and thin the stalks(pull some up) if you want larger potatoes. Good luck!

Something to keep in mind. Store bought potatoes as opposed to "seed potatoes" are sometimes treated to retard sprouting. So they may or may not sprout at all and may or may not do well if they do.

If you think your sweet potato may have been waxed to prevent it from growing scrub it

1st method
start slips with a sweet potato cut in half lengthwise
Lay the cut side in a shallow pan of wetted sand
Cover tightly with plastic wrap until sprouts appear
unwrap

The slip is ready when it has 4 or 5 leaves
4 to 8 inches tall
and has roots


2nd method:
place a whole potato in a jar
cover the bottom inch with water
keep warm

when leaves form above the roots
twist sprouts off and plant in flats or outside (if warm enough)

or
when rooted plant in 6 inch pots set in a south facing window for the duration of the winter


To plant:
prepare the ground (in zone 7) this is April (65-95 degrees)
your planting depth is 4-6 inches
fill furrows with 1 to 2 inches of compost

Fertilizer:
Rock Phosphate rock potash compost mix
(may use bone meal/ compost mix but is frowned upon by some)

Note: Likes sandier soils that drain well with a slightly acidic Ph 5-0 to 6.0
Light feeder, Low Nitrogen,
Dry to medium water
water well the first few days and then cut back on water
good drainage is crucial

Good things to know:
Grows well with corn, radishes, summer savory and tansy
in warmer climates attracts beneficial parasitic wasp ( which help to control aphids, whitefly and catepillars)

Next year save some sweet potatoes to grow your own store in a cool place making sure they do not touch (55-60 degrees) you can achieve this in a make shift root cellar simply buy a sturdy small/medium size trash can fill it with your root vegetables you plan on reusing to store place several layers of thick soy ink newspaper over and under vegetables and bury it with about 1 foot of soil on top of the container in your back yard