Yam

Updated: Sep 5

Yam is the common name for some plant species in the genus Dioscorea (family Dioscoreaceae) that form edible tubers. These species are not to be confused with the sweet potato, Ipomoea batatas, which is often referred to as a yam in the US. The tubers themselves, also called "yams", come in a variety of forms owing to numerous cultivars and related species. Yams are native to warmer regions of both hemispheres, and several species are cultivated as staple food crops in the tropics. Yams were independently domesticated on three different continents: Africa (Dioscorea rotundata), Asia (Dioscorea alata), and the Americas (Dioscorea trifida).



Yam plants are herbaceous annual or perennials with climbing or trailing vines. The vines can be smooth or prickly, reaching 10 m (32.8 ft) or more in length depending on the variety. The leaves of the plant are simple and usually oval to heart-shaped with petioles which are the same length, or slightly longer, than the leaf blade itself. Some varieties possess spikes at the bases of the leaves. The plant can produce one singular tuber or several tubers which extend from stolons from a central corm (up to 20) depending on the species. The tubers can be cylindrical, curved or lobed, with brown, grey, black or pink skin and white, orange or purplish flesh.


Table of Contents


Height(Avg)

Upto 9 feet


Width - Circumference (Avg)

Upto 1.5 feet


Approximate pH

5.5 - 7.0


Varieties of Yam


Choosing the right yam variety is not just about picking the one with a good flavor. It’s also about selecting a cultivar that fits in your garden and suits your zone. Here are some varieties of yams.

  • Chinese Yam: A native of China, this variety grows on sunny slopes and reaches about 9 feet high and 1.5 feet wide. It grows well in zones 4 to 8 and can handle all types of soil. The fruit has firm flesh and a mild taste. You can bake it, boil it, or use it in stews as a good replacement for potatoes.

  • Guinea Yam: One of the many yam species that grow in Africa. This is a giant vine with matching tubers. The average yam tuber weighs about 5 pounds. So it’s more suitable for large farms than a small to medium garden. The flesh of the yam can either be white or yellow. It doesn’t have more flavors than your average potato, so use it anywhere you’d cook potatoes.

  • Filipino Purple Yams (Ube): A relatively new variety in the American market, ube originally comes from the Philippines. The skin of the tuber is often brown, but the flesh is deep purple. It has nice flavors and cooks nicely in beef stew.

  • Okinawan Yam: A native of Hawaii, this yam is packed with taste and flavors. You can roast it to bring out the sweetness and rich flavors. The flesh is also deep purple like ube yam.

  • Japanese Mountain Yams: Japanese mountain yams are cylindrical and have pale hairy skin and white flesh. They are categorised as sticky yams and have a slimy texture. There is a traditional way to use uncooked yams. First, they have to be peeled and then thinly sliced. Then, you add them to salads. You can also use these yams to make a homemade dressing using rice wine and soy sauce.

  • Tropical Yams: These are globally famous vegetables, also known as Indian yams, cush-cush etc. These yams have thickened skins with textured skin and dry, firm white flesh. These vegetables have a bland taste, and people use them in mashed dishes.

  • White and Yellow Guinea Yams: These two yams are starchy vegetables with white flesh and light yellow skin. People use them as a substitute for mashed or roasted potatoes. In addition, you can also use them in stews and dumplings.

You might find other “yams” in the grocery store, such as American yam and golden yam. However, and despite their name and popularity in Thanksgiving meals, these are actually sweet potatoes. Both of these veggies are the kind of variety you wouldn’t want to grow in your garden simply because they have nothing to do with yam.


Planting Yam


Sun Requirements


Yams require full sun.


Soil Requirements


Yams like slightly acidic soil between 5.5 to 6.5pH. Rich loamy soil that drains well is best. Slight clay is okay, but hard compacted soil isn’t suitable.


When to Plant Yams


Plant yams indoors well before the last frost to get a good head start. You’ll either need to buy or grow slips or tubers. Plant outside once the last frost has passed and the temperature is consistently above 80°F.


Growing Yam


How To Grow Slips

  • Push three toothpicks in a yam about halfway down and place in a glass of water. Half the yam should be submerged and the other half held above the water by the toothpicks resting on the glass lip.

  • Place in a sunny window and ensure the water level stays at the same height by topping up when necessary.

  • In about three weeks, the yam will sprout slips that grow from the part of the yam not in the water.

  • When the slips form a couple of leaves, gently twist the sprouts off.

  • Lay the sprouts in a shallow dish with the bottom in water and the top leaves hanging over the side to help form roots.

  • When the roots are about an inch long or more, they’re ready to plant.


How To Grow Tubers


Use a healthy yam tuber and cut in half or quarters ensuring each piece has an eye that will grow a plant, the same as you chit potatoes. Rub wood ash over the yam and allow to sit for a few days to help prevent disease.


Plant in small pots with good quality potting mix and water well. When the plant sprouts and is a few inches tall, plant outside.

Spacing


Some varieties are extremely prolific growers, so give them plenty of space. To space in a more traditional way, plant each slip 12 inches apart with 5 feet between rows. You might want to give plants a structure to trail over, like a trellis or grate. Some tubers grow big and need plenty of space. This is one plant you don’t want to grow too close together.


Care for Yam


Although the process of starting yam vines from a tuber sounds involved and lengthy, it’s easy enough for any gardener to pull it off. When the plant is about 4 weeks old, you’ll need to install a stake near its base. Be careful not to damage the roots when putting down the stake. The vines will climb on the stake and spread out.


Soil


In the wild, yam practically grows in any soil type. It only draws the line at clay soil. Since the tubers grow deep in the soil, yam prefers loose and well-drained soil. This type of soil allows it to spread out and develop its robust root system and tubers without much resistance. So if you have clayish soil in your garden, you can amend it with coarse sand and plenty of organic materials to loosen it up. As for the soil pH, you will need to test it before planting the yam sprouts. If you get a reading above or below 5.5 to 6.5, then you need to amend the soil to bring it close to those levels.


Water


One look at the dense foliage and the tubers gives you an idea of how much water yam needs. Surprisingly it’s not that much compared to plants of the same size and fruit productivity. During the first week of the yam’s sprout life, you’ll need to water it once a day. Keep the soil moist but not soaked or even wet. Once the vine starts to climb on the stake, cut back watering to once a week. The vine usually needs about one to two inches of water per week. As usual, you should factor in any rainfall in your area and adjust your watering schedule according to the amount of rain your vine gets.


Mulch


Mulching is an important part of the yam vine’s growth and success. It retains the moisture in the soil and prevents weeds from growing around the vine. Yam is not very competitive, and any issues in the soil such as pests or roots of other plants would cause it plenty of distress. So lay a 3-inch thick layer of straw or hay in a circle around the vine. Don’t let the mulch touch the base of the yam since that could cause it to rot. Mulch also protects the tubers as they grow in the soil against temperature fluctuations.


Fertilizer


If you plant yam in rich soil, then you won’t have to worry about fertilizing it. As long as the soil has plenty of organic materials, then the vine will grow at a fast rate without issues. However, poor soil impacts the growth and productivity of yam. So ensure you have mixed plenty of rotted manure or compost in the soil before planting the yam sprout. When the vine starts to climb the stake, feed it with a custom 6-12-12 fertilizer. The fertilizer should be low in nitrogen but high in phosphorus. This will encourage the vine to focus on developing tubers rather than growing lush green foliage. Add organic compost later on an as-needed basis.


Harvesting Yam


It takes yam tubers up to 8 months from the time you start the vines to become ripe. That’s a long time for a plant to grow in the garden. Usually, by mid-fall, the yams are ready to harvest. The first sign is the leaves turning yellow and falling off the vine. Give it another couple of weeks before you start digging for the ripe tubers.


Use a fork and start at the base of the vine. Follow each tuber underground, then cut it off with a clean blade. Store the tubers without washing the dirt off them.


Pests and Diseases


Both mealybugs and white scale insects are the main bugs you have to worry about when growing yam. Mealybugs go after the sap in the leaves and spread diseases in their wake. Kill them with neem oil, or spray the vine with diluted alcohol. White scale insects, on the other hand, are attracted to the tubers. If left unchecked, they could damage the tubers and impact your crop. Use neem oil to get rid of these pests safely.


As for diseases, watch out for yam mosaic disease. It’s often spread by bacteria that aphids carry. The symptoms include lesions in mosaic patterns on the leaves, and it leaves the tubers shrunk in size and lacking starch and flavors. Remove infected leaves, keep aphids at bay, and remove any weeds around the vine.


Dry rot disease also causes lesions on the tubers. These lesions later make their way into the flesh of the tuber, causing them to crack. To prevent this disease, rub your tuber with ash before you get it to sprout. Ash kills the nematodes that cause dry rot disease.


Benefits of Yam


Yam looks like a tacky vegetable. It contains numerous health benefits, including:

  • Yams are rich in fibers and resistant starch, which improves our gastric health and promotes good gut bacteria. Consuming them reduces appetite, so yam helps in weight loss.

  • Yam contains a decent amount of vitamin B5, thiamine, folate, and vitamin C, which boost our immune system and are beneficial for growth and bone development.

  • Yams are rich in many minerals, such as manganese, magnesium, and potassium, which are beneficial for bone health, decrease cholesterol levels, and proper functioning of our heart.

  • Daily consumption of yam increases estrogen hormones (especially estrone and estradiol), which helps ease post-menopausal symptoms in women.

  • Yams contain a reasonable amount of antioxidants, which reduces the risk of many cancers.

  • Yam is rich in anti-inflammatory agents and antioxidants, which help manage many chronic inflammatory conditions such as heart diseases, irritable bowel syndrome, and stomach ulcers.

  • Diosgenin present in yam encourages neural growth and amplifies memory and brain functioning.

  • Eating yam, especially the purple variety, helps decrease fasting blood sugar levels and hemoglobin A1c (HbA1c) levels in our blood.

Nutrient-dense yams are a highly beneficial and versatile vegetable. We can add them to our diet in various ways, such as baked, boiled, mashed, curries, or yam chips and fries. So, add them to your diet to enjoy its countless health benefits.


Uses

  • Yams are consumed after cooking by frying, boiling or roasting.

  • The green parts of some plants can be cooked and consumed as a vegetable.

  • Yams may also be used to produce flour or starch.

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