Sweet potatoes and regular potatoes are often assumed to be closely related due to their shared name and similar appearance as underground vegetables. This belief is inaccurate, as they are not distant botanical relatives and are not grown in the same way. The distinction is fundamental, rooted in their biological classification and the function of their edible parts. Understanding these differences clarifies why their cultivation methods are so distinct.
Botanical Identity and Classification
The most significant difference between the two plants is their scientific classification, placing them in entirely separate plant families. The common or white potato, Solanum tuberosum, belongs to the Solanaceae family, known as the Nightshade family. This family also includes vegetables such as tomatoes, eggplants, and peppers.
In contrast, the sweet potato, Ipomoea batatas, is a member of the Convolvulaceae family, recognized as the Morning Glory family. This family includes ornamental morning glories and bindweeds. The two plants are not classified within the same genus, emphasizing that their similar names are a matter of culinary tradition, not biological relationship.
The Difference in Edible Structure
The fundamental biological difference stems from which part of the plant is enlarged and consumed. The common potato is a true stem tuber, an enlarged, underground stem that stores nutrients, primarily starch. As a modified stem, the potato tuber possesses characteristics of above-ground stems, including nodes and internodes. The familiar “eyes” on a potato are buds or nodes capable of sprouting new shoots and roots.
The sweet potato, conversely, is a storage root (or tuberous root), a specialized, thickened root structure. This storage root grows directly from the plant’s root system, not from underground stems like the potato. Because it is a true root, it lacks the nodes and internodes characteristic of a stem. This distinction explains why a cut piece of sweet potato will not sprout in the same manner as a white potato.
Cultivation Methods and Planting Materials
The biological difference between a stem tuber and a storage root dictates their separate propagation methods. Regular potatoes are planted using seed potatoes or cut pieces of the tuber containing at least one or two “eyes.” These eyes are buds on the modified stem that directly sprout the new plant’s stem and foliage. This method is a form of vegetative reproduction capitalizing on the stem tuber’s structure.
Sweet potatoes are grown from specialized cuttings called slips, not pieces of the root. A slip is a rooted shoot or sprout taken from a mature sweet potato. Growers initiate slips by bedding mature storage roots in soil or water to encourage sprout development. These rooted sprouts are then detached and transplanted into the garden soil to develop new storage roots.
The need for slips also highlights the differing environmental needs of the two crops. Sweet potatoes are tropical plants requiring a long, warm growing season and warm soil temperatures. They are often planted three to four weeks after the last frost date. Regular potatoes are more tolerant of cooler soil and are generally planted earlier in the spring.