Dozens of common foods grow underground, from everyday staples like potatoes and carrots to surprises like peanuts. These foods fall into distinct botanical categories based on which part of the plant swells with stored energy beneath the soil. Understanding these categories helps explain why underground foods look, taste, and behave so differently from one another in the kitchen and in the ground.
Taproots: Carrots, Beets, and Their Relatives
A taproot is a plant’s primary root, thickened and swollen with stored sugars and nutrients. It grows straight down, anchoring the plant while doubling as a pantry. Carrots are the most familiar example, packed with vitamin A and available in orange, purple, white, and yellow varieties. Parsnips look similar in shape but are white, sweeter, and rich in vitamin K. Beets store folate, potassium, and manganese beneath their earthy sweetness, and they come in deep red and golden types. Radishes round out this group with a peppery bite and a remarkably fast growth cycle of just 25 to 30 days from seed to harvest.
Other taproots include turnips (40 to 60 days to maturity), rutabagas, celeriac, and jicama. All of them share the same basic structure: a crown of stem tissue sitting on top of a fleshy, swollen root that does the heavy lifting of energy storage.
Tubers: Potatoes and Their Look-Alikes
Tubers are not roots at all. They are swollen underground stems, packed with starch that the plant stores as an energy reserve. The potato is the classic example, reaching harvest in about 70 to 90 days. Those “eyes” on a potato are actually buds, each capable of sprouting into a new plant. The entire potato is fleshy stem tissue throughout, which distinguishes it from bulbs and corms.
Plants store energy underground in two main forms: insoluble starch packed inside cell structures, or soluble sugars held in fluid-filled compartments. Potatoes lean heavily toward starch, which is why they’re one of the most calorie-dense vegetables. A baked white potato has a glycemic index of 85, meaning it raises blood sugar quickly. Sweet potatoes, by contrast, score around 54 on the glycemic index. That’s partly because sweet potatoes aren’t true tubers. They’re tuberous roots, meaning they are thickened lateral roots rather than swollen stems. Sweet potatoes take 90 to 120 days to mature and need warm soil to develop properly.
Jerusalem artichokes (sunchokes) are another edible tuber, storing their energy primarily as a type of soluble fiber rather than starch, which gives them a different texture and nutritional profile.
Bulbs: Onions, Garlic, and Shallots
A bulb is a compact underground stem wrapped in thick, fleshy layers called scales. Onions are the most common edible bulb. If you slice one in half, you can see those concentric layers clearly, each one a modified leaf packed with stored nutrients. At the bottom sits a flat disc of stem tissue called the basal plate, which sprouts roots downward and sends shoots upward.
Garlic, shallots, and leeks belong to the same plant family. Bulbs grow new layers from the inside out and reproduce by forming small offsets (called bulblets) around the basal plate. Dry bulb onions need 100 to 120 days to reach maturity, making them one of the slower underground crops. They also have a papery outer covering called a tunic, which protects the moist layers inside and helps the bulb last in storage.
Rhizomes and Corms
Rhizomes are horizontal stems that grow sideways just below the soil surface. Unlike roots, they have nodes, and from each node a rhizome can send roots downward, shoots upward, and branches outward to create new plants. Ginger is the most widely eaten rhizome. Turmeric, galangal, and lotus root also fall into this category. These foods tend to be aromatic and fibrous because their branching structure prioritizes spreading over bulking up.
Corms look similar to bulbs from the outside, with a papery covering and a basal plate, but slicing one open reveals solid tissue rather than layers. Taro is the best-known edible corm and a dietary staple across the Pacific Islands, West Africa, and parts of Asia. New corms grow either from a bud on top of the old one or from small “cormels” that form around the base.
Peanuts: A Fruit That Buries Itself
Peanuts are one of the most unusual underground foods because they are technically fruits, not roots or stems. The peanut plant flowers above ground, but after pollination something remarkable happens. The fertilized flower stem elongates and curves downward, physically pushing into the soil. The seed pod then develops and matures entirely underground. This process is called geocarpy, and the peanut’s species name, hypogaea, literally means “under the earth.”
This makes peanuts a legume that behaves like a root crop. They’re the only widely eaten nut (botanically a legume) that grows this way, which is why they’re also called groundnuts.
Tropical Staples: Cassava and Yams
Cassava is the second most important starchy root crop in the tropics, after the sweet potato. It originated in Mexico, Central America, and northeastern Brazil, and was carried to West Africa by Portuguese traders in the sixteenth century. It didn’t reach Southeast Asia until the mid-1800s. Today it grows throughout the tropical belt, mostly between 20°N and 20°S latitude, feeding hundreds of millions of people.
Raw cassava contains hydrocyanic acid, a naturally occurring toxin found in the roots, branches, and leaves. Sweet varieties concentrate the toxin mostly in the skin and outer layer, while bitter varieties contain it throughout. Sweet cassava roots have less than 50 milligrams of hydrocyanic acid per kilogram of fresh weight. Soaking the roots in water, cutting or crushing them, and heating all accelerate the breakdown of this compound, which is why cassava is always cooked or processed before eating. True yams, which are large starchy tubers common in West Africa and the Caribbean, are a separate crop entirely from sweet potatoes despite frequent confusion between the two in North American grocery stores.
Why Soil Type Matters
Underground foods are shaped, sometimes literally, by the soil they grow in. Loamy soil, a balanced mix of sand, silt, and clay, is ideal for most root and tuber crops because it holds enough water for the plant without staying waterlogged. Compacted clay soil drains slowly, which can cause rot and produces stunted, misshapen roots. Carrots and parsnips in heavy clay often fork and twist as they struggle to push downward. Sandy soil drains quickly and lets roots expand easily, but sand and silt don’t store nutrients the way clay particles do. That’s why gardeners amend sandy beds with organic matter to feed the crop.
Potatoes prefer slightly acidic, loose soil. Sweet potatoes need warmth and can’t tolerate temperatures below 50°F. Radishes are forgiving and grow fast in almost any well-drained bed, which makes them a common starter crop.
Storing Underground Foods After Harvest
One reason underground foods have been so important throughout human history is their natural storage life. The same energy reserves that feed the plant through winter also keep these foods edible for months under the right conditions.
Most root vegetables, including carrots, beets, parsnips, turnips, and horseradish, store best in cold, very moist conditions: 32 to 40°F with 90 to 95 percent relative humidity. A traditional root cellar mimics these conditions. Potatoes need it slightly warmer, ideally 38 to 40°F with 80 to 90 percent humidity, and should be kept away from fruit. Fruits release ethylene gas, which causes potatoes to sprout faster.
Sweet potatoes are the exception. They need warm, moist storage and will spoil if temperatures drop below 50°F. Onions go the opposite direction, preferring cool, dry air at 32 to 35°F with only 60 to 70 percent humidity. Storing onions in the same humid bin as carrots will cause them to soften and rot. Keeping these preferences straight is the difference between root vegetables lasting a few weeks and lasting several months.
Nutritional Range Across Underground Foods
Underground foods span a wide nutritional spectrum. Carrots have a glycemic index of just 39, making them a relatively low-impact choice for blood sugar. Sweet potatoes sit at 54. Baked white potatoes spike to 85, one of the highest values among whole vegetables. This range means that “root vegetables” is not a single nutritional category, and choosing among them can meaningfully affect how your body responds.
Carrots are best known for vitamin A. Beets deliver folate and potassium. Parsnips provide vitamin K and zinc. Potatoes are high in potassium and vitamin C, though much of the vitamin C is lost in cooking. Cassava and yams are primarily calorie-dense starch sources with less micronutrient variety, which is why cultures that depend on them often pair them with leafy greens, fish, or legumes to round out the diet. Ginger and turmeric, while eaten in small quantities, contain bioactive compounds that give them their strong anti-inflammatory reputations.