You plant sweet potato slips outdoors in warm spring soil after all danger of frost has passed, spacing each rooted sprout twelve to eighteen inches apart. Dig small holes about three to four inches deep in loose, well drained soil and bury the bottom half of the slip while leaving the top leaves exposed. Water the newly planted slips thoroughly right away to help the roots establish quickly in the warm earth. Keeping the soil consistently moist during the first two weeks ensures healthy vine growth.