Sweet Potato Cultivation in the Upper Valley 

Starting Plants with Slips That You Have Ordered
If this is your first year, order the slips (plants) from a seed catalogue or other grower. That way you will be able to choose your varieties carefully. There are several that are especially recommended for growing in the north:

Beauregard. Vines 6–8 feet. Mid-season. Red-orange skin, orange flesh. A very productive variety with elongated roots and good flavor. Good keeper.

Carolina Ruby. Vines 8–12 feet. Mid-season. Deep garnet skin, dark orange flesh. High yield, roots grow right under the plant. Good keeper.

Georgia Jet. Vines 6–8 feet. Early. Pinkish skin, orange flesh. Can produce very large roots that sometimes crack. The flavor is good but not outstanding. Very productive. Good keeper.

Red Yam. Vines 4–6 feet. Early. Red skin, deep orange flesh. A bit of a misnomer, since yams and sweet potatoes are from completely different plant families. Above average yield, good keeper.

Vardaman. Vines less than 4 feet. Mid-season. Light orange skin, orange flesh. Purple leaves. Average yield. Very sweet flavor. Good keeper.

The slips you receive in the mail may or may not already have small roots. Technically you can plant even the ones that haven't rooted. But they will do best and survive transplant best if you suspend them in water for a few days first. Once they have small roots they are ready for planting out. Very large root systems are not necessarily better.

Starting Your Own Slips
If you have sweet potatoes growing in the garden you can start your own slips for the next year in a few ways. No matter which method you choose, be sure to label the different varieties.

Method 1: From Cuttings.  Before the first fall frost, cut about 4 inches from the tips of several vines. Place these in water until they root. Once rooted, pot them up and keep them alive over the winter. In early spring, the plants will begin growing again. At this point, pinch back the tips.This will encourage the plants to branch. Each original cutting will now produce around 3 or 4 new branches (or slips). About 10 days before planting out, cut these branches (slips) and place them in water until they root. These are your new sweet potato plants for the garden.
          

Method 2: From Tubers Sprouted in Soil.  At the end of the winter, take sweet potatoes around 1 1/2 inches in diameter and about 3 inches long. Lay them, not touching, on their sides in a flat. Cover with about 2–3 inches of potting mix. Cover the flat with plastic film to hold in heat and moisture. Left in a warm spot, the roots will produce shoots in about 3–4 weeks. When the shoots have reached  4–6 inches, gently twist them from the tubers and place them in water to root. In about 10 days you will have rooted plants ready to go out.

Method 3: From Tubers Sprouted in Water.  About 4 weeks before planting out, suspend the lower half of a sweet potato in water by sticking toothpicks in its sides. The root will sprout sooner if you have that end up which was attached to the plant while it was growing. Twist 4–6 inch sprouts from the tuber and root in water before planting out. Calculate about 10 days for the slips to root and be ready for the garden. 

          

Planting Out and Cultivation
Wait until the soil has warmed up to at least 65°F before planting sweet potatoes. You will have a higher yield if you plant later, in warmed up soil, than if you plant earlier in cool soil. You can warm up the soil using black plastic, then cut holes in it at 12–24 inch spacing for the slips. Plant slips and water well for several days until they are established. After that water only sparingly. Sweet potatoes prefer sandy, well-drained soil and hot, dry conditions. Do not overfertilize or you will get long, skinny roots. You can also use floating rowcover, which will increase heat around the plants and protect them from deer, who love the leaves. Mulching around the plants—if you are not using black plastic—keeps weeds down and prevents the vines from setting roots along their length, which would reduce yields. It is entirely possible to grow adequate yields without either black plastic or row cover.

Harvesting
Most varieties mature in 90 to 120 days. Keep the roots in the ground for as long as possible, but after the soil temperature sinks below 55°F they will become susceptible to fungus, so dig them before a hard frost. This is also the time to take vine cuttings if that is going to be your chosen method for propogating the plants. Cut the vines back to the base of the plant to make digging easier. Dig the roots very carefully, they are extremely susceptible to bruising and breaking at harvest time. It is also possible for some of the roots to form far from the base of the plant, so follow those skinny roots! Brush the dirt off, or wash them.

Curing
Cure the roots at about 85°F and 95°F humidity for about 5 days before storing. This can easily be done in an old, turned-off refrigerator or upright freezer with wire racks. Place the roots on the racks not touching each other. Place basins of water in the bottom. Suspend a work light with a 25W bulb above the roots. Tape the door shut and leave undisturbed for 5 to 7 days. Otherwise any warm spot will do, just make sure there is adequate humidity.

Storing
Sweet potatoes should be stored at 55°F–60°F over the winter. Under ideal conditions, they will keep until April. Curing does not affect the ability of the roots to be sprouted in the spring.

Sources of Slips—Here are Just Two
Sand Hill Preservation Center. www.sandhillpreservation.com. Dozens of varieties to choose from. One of the best sources. Very reasonable prices.

Pinetree Garden Seeds. www.superseeds.com. Beauregard, Georgia Jet, Vardaman.

Click here to link to MOFGA site about growing sweet potatoes