Thinking that yams and sweet potatoes are the same veggie is common but untrue! While sweet potatoes are yellow-orange due to their high levels of beta-carotene, yams are usually white or purple and can weigh up to 7 lbs. These tubers naturally hail from the Caribbean and Southeast Asia, but these days Africa is the largest cultivator. Yam plants are perennial vines with purple-tinged heart-shaped leaves that require a trellis or support structure for growth.
The Purple Yam was first cultivated in Southeast Asia but is now grown in Hawaii, the southeastern US, Australia, and Africa. Tubers are usually a bright lavender color and add a rich purple hue to roasts and mashed yam recipes.
Seed: Not grown from seed.
Vegetative: Yams are propagated by planting tubers or slips.
Tuber Depth: 1–2″
Space Between Plants: 3–5′
Space Between Rows: 5–7′
Sprouting Soil Temperature: 70°F
Days for Sprouting: 21–27
Start Indoors: In early spring if the ground outside is too cold.
Start Outdoors: In early spring after all danger of frost has passed.
Plant at the beginning of summer in areas that exhibit wet summer seasons. The yam prefers a warm climate of about 77–86°F and cannot tolerate temperatures below 60°F very well. Native to tropical and subtropical areas, this plant thrives in USDA Zones 10 and above. Photo-periods are important in the cultivation of yams: shorter days promote tuber growth, while longer days promote vine growth.
Natural: Full sun to partial shade.
Artificial: Grows well under fluorescent or metal halide HID lamps. Equivalent to full sun, or 6-12 hours of light per day.
Soil: Prefers a sandy or loamy soil that is fertile, well-drained, and high in organic matter. Because this is a root vegetable, deep soil is a must. These tubers enjoy an acidic pH of around 5.5. Add lime to achieve this low pH if necessary.
Soilless: Grows well in a soilless mix containing coco coir and perlite.
Hydroponics: Will thrive in hydroponic systems, especially deep water culture.
Aeroponics: Can grow in aeroponic systems (see attached PDF in Helpful Links for more info).
Water: Requires low to moderate levels of water. Quite drought tolerant, but in areas of drought lasting over 3 months, irrigation is recommended.
Nutrients: Requires moderate levels of nutrients. Fertilizers are commonly added twice during the season, once about a month after the plant breaks the soil and again during bulking of the root vegetable. It’s best if fertilizer is added about a foot away from the base of the plant.
Foliar: Take care when using oil-based or insecticidal soap sprays: burning via magnification of the sun can kill entire plants. We recommend spraying in the early morning or evening.
Mulching: Mulch to retain soil moisture and protect from excessive heat and desiccation. Mulching will also minimize unwanted weed growth.
Deficiency(s): Subject to iron deficiency. Alkaline soils can lock iron, so lime the soil to lower pH and allow easier access and increased iron uptake.
Rotation: Rotation is important to avoid nematode proliferation. It may be a good idea to rotate yams with marigolds.
Companions: Grows well with nitrogen fixers, such as snow and snap peas, and aromatic herbs that repel insects, such as savory, oregano, basil, and dill. Overall, the yam is an aggressive plant and will most likely overgrow companions. However, if you plan things well, you can harvest from the companion plants before that happens.
Marigolds are also a good choice for a companion to the yam. In addition to their natural insect repelling abilities, the roots of the marigold release a repellent underground that shoos nematodes away. The effects of this can last up to 3 years.
Harvest: Gently harvest when you notice leaves and foliage are yellowing, usually around late November. This is a sign that all energy is being put towards tuber bulking. Tubers are often dug out with a tool called a bolo, or you can use a shovel or pitchfork to loosen the soil. Remove all loose soil then leave them in a warm, dry place for 1–2 weeks to cure. Tuber dormancy lasts about 3-4 months after harvest. During this time, it is either eaten or saved for replanting.
Storage: Use within 2 weeks if yams are kept at room temperature. Dark, cool (50°F), and dry areas will stretch out tuber dormancy and will obstruct sprouting. They can keep for up to 1–2 months in these conditions. Do not refrigerate.
Fun Fact: D. alata is considered an invasive species in some states of the southern US, including Florida and Georgia.
Preserve: Stores well in the freezer. Cook or steam until partially soft. Cool to room temperature, peel, cut into halves, place into bags and freeze.
Prepare: Yams are great candied, roasted, stir fried, or mashed. They can be interchanged with sweet potato in most recipes. It can also be processed into a starch.
Nutritional: A good source of potassium and vitamin C.
Medicinal: A natural antioxidant which may provide health benefits. Traditionally, it has been used as a laxative, to rid patients of parasitic intestinal worms, and as a treatment for fever, gonorrhea, leprosy, and hemorrhoids.
Warnings: Eating yams raw can be unappetizing and unsafe. Always cook before eating.