Planting and Growing Sweet Potatoes

Sweet potatoes, Lpomoea batatas, are not related to potatoes, they are actually a member of the morning glory family. Sweet potatoes are tuberous roots and not a true tuber. Most common sweet potatoes have a dark orange flesh (can also find purple, red or white) and skin. Sweet potatoes are not yams and yams are not sweet potatoes. Yams (are in the lily family) have a brown bark-like skin and have either white or purple flesh and can grow up to 7 feet long. They are also not widely available in the U.S.

How to Grow Sweet Potato Slips

Sweet potatoes are grown from slips, which is a rooted sprout from a sweet potato. Slips are easy to grow from a mature sweet potato but will take about 8-12 weeks before you are ready to plant. So start sprouting your sweet potato around February to March or around 3 months before you are ready to plant. There are a couple of ways to start your slips but the easiest and fastest method is to place your whole sweet potato in a tray of soil, set horizontally and covered half way with medium. You can either use potting soil, Quickroot or perlite (does not produce slips as fast as potting soil). Don’t try to sprout a conventional store bought sweet potato as they are often treated with a sprouting inhibitor. You can try an organic sweet potato since most likely they are not treated with any chemicals.

Growing Your Slips

  • Fill a tray half way with potting soil or Quickroot and moisten.
  • Put your whole sweet potato on top of the soil horizontally and add about an inch of soil but do not completely cover.
  • Place the tray on a heating mat, and to speed up the sprouting, place your tray under a grow light.
  • Keep the soil moist but not soggy
  • In about a week, there should be roots coming from the bottom and small sprouts forming on the top or sides.
  • Allow the sprouts to grow to at least 6 inches long.
  • This process will take about 4-6 weeks.

Rooting the Slips

  • Once the sprouts are at least 6 inches long remove them from the sweet potato by cutting them off at the potato. Some may have already begun to form roots if located along the bottom portion of the sweet potato. Just tease them out of the soil, trying not to break of any roots that are formed.
  • Remove the lower leaves from the sprouts and place in a jar or glass of water to allow roots to form.
  • To speed up the process you can place the jar on a heating mat or under a grow light. Roots should start forming in a couple of days.
  • Change out the water once a week and remove any sprouts that have died and are not forming roots.
  • Once the sprout has roots that are about 2-3 inches long you are ready to plant your slips.
  • One whole sweet potato can yield about a dozen or more sprouts. You may have more slips than you can handle in your garden. Give them away to friends, family or to a school or community garden.

Planting Your Sweet Potato Slips

Sweet potatoes are tender (do not tolerate any cold temps) and your slips should not be planted until all danger of frost is past (about 2-3 weeks after the last frost) and when the soil has warmed to about 65°F.

Soil and Sun

Plant in well-drained loose soil that is slightly acidic (around 6.5). If your soil is clay, amend it with compost. Soil should be loose to at least 8-10 inches deep. If your soil is very compact and poor draining, you can plant in a raised bed or large containers such as a Smart Pot (one slip in a 20 gallon size). Plant in full sun or if in a very hot region, put in an area that receives some afternoon shade or you may need to use some shade cloth.

Plant your slips deep so just the top leaves are exposed. Space plants about 12-18 inches apart. Water well and make sure to fertilize with a higher phosphorus mix (if your soil is deficient). Plants produce long vines that will want to root, don’t allow the vines to root since it will take energy away from tuber formation at the main plant. To avoid this from happening you can grow the vines on a trellis, keeping them off the ground.

Watering & Feeding

Deep water your plants but do not overwater. The soil should dry out a little between waterings. Sweet potatoes do not tolerate soggy soil. If your soil does not have adequate phosphorus, you should feed with a higher phosphorus fertilizer. Do not over feed with high nitrogen, or you will have great vines but little formation of tubers.

Harvesting, Curing and Storing Your Crop

Harvesting

Sweet potatoes take between 90-120 days to mature (depending on variety) so the longer they can be in the ground the better the yield. Tubers should be harvested when they are at least 3 inches in diameter and should be lifted before the first fall frost. When the leaves start to turn yellow is a good sign that your sweet potatoes are almost ready for harvest. Once the vines have died back, you can begin harvesting.

  • Remove the vines and find the original crown, carefully loosen the soil with a digging fork or shovel. Don't dig too close to the original plant or you can damage any sweet potatoes in the ground. 
  • Once the soil is loose, use your hands to dig up the tubers. Remove any excess dirt but do not wash them, this will shorten the storage life of the sweet potatoes.
  • Any sweet potatoes that were damaged during harvest should be used right away.
  • For the longest storage make sure to cure your sweet potatoes

Curing

  • Set them in a location out of the direct sun and that is warm (about 80°F) and humid.
  • Place them in a single layer making sure no sweet potatoes are touching each other.
  • Cure for about 10-14 days. This allows any scratches or cuts to heal and also helps the starches in the sweet potatoes to convert to sugars.
  • If sprouts start to appear, they have been cured too long and they should be consumed right away.

Storing Your Cured Sweet Potatoes

For the longest storage, place in a cool (55-65°F) dry area. Do not store your sweet potatoes in the refrigerator. Monitor for any rotting sweet potatoes and remove them right away. If stored under proper conditions, sweet potatoes can last 4-7 months.

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