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Growing Guide: Sweet Potatoes

A pile of orange-pink sweet potatoes of various shapes

Growing Sweet Potatoes: A Complete Guide

Although similar in name, sweet potatoes are quite different from potatoes. Growing sweet potatoes has different requirements than growing potatoes. Sweet potatoes also belong to the morning glory family, and not the nightshade family like regular potatoes. But similar to potatoes, sweet potatoes have various shapes, sizes and colors.

Sweet potatoes have significant cultural and culinary histories and uses across the globe. Sweet potatoes originated in Central and South America, but early on traveled across the pacific. Using radiocarbon dating, archaeologists discovered prehistoric sweet potato remnants in Polynesia dating back to A.D. 1000 to A.D. 1100.

Seed Savers Exchange does not currently sell sweet potato seed, slips, or plants. However, several listers offer sweet potato varieties on The Exchange.

How to Grow Sweet Potatoes

Time of Planting

Plant sweet potatoes outside when the danger of spring frost has passed, and average temperatures have reached at least 70°F. Sweet potatoes need warm temperatures, so there is no need to hurry and plant them early.

Spacing Requirements

When planting in rows, space plants 12-18 inches apart within a row. Space the rows 3-4 feet apart.

Obtaining Slips

Sweet potato plants grow from slips, as opposed to seed. A slip is a portion of a mature sweet potato that has rooted. To obtain a slip from a tuber, cut a sweet potato in half lengthwise. Bury the slip in damp potting soil indoors.

The time to germination differs between varieties. Generally, sweet potato slips should sprout shoots within a few days after planting when kept in a warm and moist environment.

Transplant the sweet potato slips outside about 6 weeks after shoots sprout. Wait to transplant the slips until the shoots are 4-6 inches tall.

Tip: Instead of sourcing sweet potatoes from the grocery store, buy your slips or seed potatoes from a trusted distributor. This will help to ensure the potatoes are disease-free.

Planting Considerations

Find a sunny planting site with healthy, well-drained soil. Sweet potato plants prefer full sun, but can tolerate partial shade in a hot and dry climate.

To prepare the soil, till and lay black plastic or black landscape fabric over the rows to help raise the ground temperature. Cut slits in the fabric and plant each slip accordingly.

Tip: Place a flag at the origin of planting. This will help guide digging during harvest.

Water the transplants at planting time. Water well for the first week after planting, or until the sweet potato plants do not look wilted. Generally, the plants should look great after a week of good heat and water.

Sweet potatoes thrive in sandy, well-drained soil. If planting in heavy clay soil, build a mound the length of the row about 12-15 inches high and 18 inches wide. Cover the top of the mound with fabric and follow the instructions above.

Season Maintenance

Check your sweet potato plants often. Carefully pick up each vine beginning at the flag and lift to prevent rooting. This allows more energy to go to the main plant which will in turn produce larger sweet potatoes. Routine irrigation during the season is unnecessary unless the plants look wilted.

Common Pests and Diseases

Deer love the sweet taste of the plant’s leaves. Use appropriate methods to protect your crops from deer. Check out this method to DIY an inexpensive deer fence.

Some common pests include the sweet potato stem borer and the white grub. Sweet potato stem borer larvae bore into the stem to feed. The white grub feeds underground on the stem or roots. To manage these pests, keep the garden area weed free, till the soil thoroughly before planting, and provide proper drainage.

Sweet potatoes are vulnerable to a range of diseases. Inspect your plants often to detect any diseases early on. To prevent disease, maintain good soil health, and only plant disease-free slips.

Clear all remaining plant material from the soil after harvest. Additionally, you can try disease-resistant varieties.

Alternaria leaf spot is a fungal disease that creates brown lesions on leaves. If left untreated, it can harm the plant’s health and the soil in the affected area.

Check your plants for disease often. Remove and destroy any infected material. To prevent the spread of the disease, disinfect your pruning tools.

To prevent alternaria leaf spot, clear the soil of all residual sweet potato material immediately after harvest. Keep the soil healthy and well-drained. Use mulch and plant disease-resistant varieties.

Blackleg, also called black rot, appears as dark circles on sweet potato tubers or stems. It can cause plants to develop poorly or die. You cannot treat blackleg, so you must remove any infected plants.

To prevent blackleg, plant only disease-free slips in well-drained soil. Avoid injuring the sweet potatoes at harvest and store tubers in a cool, dry place over winter. Rotate crops year to year and practice good hygiene when removing infected plants.

Harvesting Sweet Potatoes

Most sweet potato varieties require an average of 4-5 months to reach maturity. Harvesting in mid-September is a good general recommendation, however the most optimal time depends on your local weather. Harvest the tubers when the foliage turns yellow.

Harvest sweet potatoes before the soil temperature reaches 55° to prevent mold. This will also keep your harvest fresh for a longer period.

You can find most of the sweet potato crop growing below its main plant (the flagged area). However, tubers can sometimes grow parallel to the soil line, so be careful when digging. Handle the sweet potatoes minimally. Handling sweet potatoes is likely to bruise or damage them, which shortens their shelf life.

At harvest, brush off large clumps of soil being careful not to rub off any of the tender skin. After the curing process, it will be safe to remove excess soil from the sweet potato tubers.

Curing Sweet Potatoes

To cure, place tubers in a warm place and out of direct sunlight, with an optimal temperature of around 85° F and high humidity. Let them sit for one week.

Storing Sweet Potatoes

To store, place the sweet potatoes in a ventilated plastic container in a shaded/dark area. The room temperature should ideally be around 60-70° F.

Check on the sweet potatoes often in storage and remove any that have rotted. Save your best tubers, also known as seed potatoes, to plant in the next spring!