Growing sweet potatoes is fun and easy, and a great way to enjoy super-sweet tubers that taste so much better than those you’ll find at the local supermarket. If you’re wondering how to grow sweet potatoes in your home vegetable garden, I’ve got all the information and advice you need to get started.
Sweet potato or yam?
There’s been some confusion about yams and sweet potatoes, so let’s set the record straight. Yams are a tropical crop grown mainly in the Caribbean and Africa. The yams I see in my local supermarket generally have brown, bark-like skin and white flesh that is starchy, like a white potato, when cooked. The roots vary in size and color, with some yams growing small and others getting several feet in length.
The confusion between yams and sweet potatoes comes from the fact that for many years orange-fleshed sweet potatoes were incorrectly called yams. Sweet potatoes originate from Central and South America. They produce tubers with tan, pinkish, purple, red, or copper skin and white, purple, or dark orange flesh.. The tubers have tapered ends and a delicious sweet flavor. Sweet potato plants form beautiful vines, but gardeners with less space should opt for those with compact vines.
Now that we’ve cleared that up, are you ready to learn how to grow sweet potatoes? Read on!
Choosing sweet potatoes to grow
Traditionally, sweet potatoes, which are a member of the morning glory family, Convolvulaceae have been a crop grown in mild climates that offer months of warm weather. Yet, thanks to plant breeders who have been selecting for fast maturing sweet potatoes, we now have a wonderful selection of cultivars that can be grown in areas with a short growing season. However, you still need around 100 days of frost-free weather to grow a bumper crop of sweet potatoes.
I’ve had great success with short-season varieties like Korean Purple, Beauregard, and Georgia Jet, but there are many cultivars to choose from in seed and speciality catalogs. Just keep in mind that you won’t be ordering seed potatoes, as with potatoes, but instead will be buying slips. Slips are the shoots that grow from a sweet potato. You can also start your own slips or buy them from a garden centre in spring to plant in your garden.
How to grow sweet potato slips
Starting your own slips isn’t difficult and you can use a sweet potato from last year’s harvest, from the grocery store (see my advice below about this though), or the farmers market. Look for blemish and disease-free tubers. Depending on how many plants you want, you’ll likely need a few sweet potatoes for slip starting. Each tuber can potentially grow several dozen slips.
Once you’ve got your sweet potatoes, there are two main ways to produce slips:
- Stick toothpicks in the top third of your potato and set it in jar filled with water so the bottom two-thirds is underwater.
- Place the whole sweet potato on its side in a pot, seeding tray, or shallow container filled with a pre-moistened, high-quality potting mix. Fill the container so the potting mix covers the bottom half of the sweet potato.
Place your jars or containers of sweet potatoes in a bright, warm spot and wait. The slips typically emerge in a few weeks, but sprouting may take as long as two months. This means you need to plan ahead and start your sweet potato slips about two months before you intend to plant them in the garden.
Preparing sweet potato slips for planting
Once the slips are six to eight-inches long, they can be broken off and transplanted into the garden (they’ll likely have some baby roots attached). If it’s not yet time to move them to the garden, pot them up in four inch pots filled with moistened potting mix. You can also put the just-clipped sweet potato slips in a jar of water so the bottom half of the stem is underwater. If there are no roots, they’ll emerge in around a week. Change the water often to promote healthy root growth.
You do need to harden off your sweet potato slips – just as you would harden off seedlings that were grown indoors under lights. To do this, you can introduce the mother plant gradually to outdoor growing conditions about a week or two before you want to snap off the slips and plant. Or, if you are removing the slips and potting them up until it’s time to transplant, you can harden off the rooted slips beginning about a week before you want to move them to the garden.
Buying sweet potato slips
I generally buy my sweet potato slips from a reputable grower like Mapple Farm because I don’t have a good cold spot to store my garden-grown sweet potatoes over the winter and I don’t like to use sweet potatoes from the grocery store. Why? Most grocery stores don’t list the variety of the sweet potatoes they carry and with such a wide range of maturity times – from 100 days to 160 days – I want to make sure I’m growing a sweet potato variety that has time to mature in my short season garden. If I order from a mail order company or buy them from a local garden centre, I can ensure that I get varieties suited to my climate. Alternatively, head to your local farmers market and if they’re selling locally grown sweet potatoes, go ahead and buy those for your slips.
How to plant sweet potatoes
Rule number one is don’t rush sweet potato slips into the garden. They need the weather – and soil to be warm. I usually plant them around the same time I plant my cucumbers and melons which is about a week or so after our last expected spring frost. If the weather is still unsettled, wait or install a mini hoop tunnel over the bed to shelter the slips.
Preparing the soil for sweet potatoes
The key to a good crop of large tubers is loose, well-drained soil. If your garden has dense clay soil consider growing in a large container or raised bed. Plant your sweet potato slips in a garden bed that has been loosened and amended with compost. Sweet potatoes are relatively light feeders but they do appreciate phosphorus and potassium, and so I work in a little balanced organic vegetable fertilizer before I plant. Avoid high nitrogen fertilizers which promote foliage growth, but often at the expense of tubers.
There are a few heat-loving crops that really appreciate you taking the extra step of pre-warming the soil, especially if you live in a short season or cold climate. I like to pre-warm the soil for my melons, peppers, eggplants, and sweet potatoes. This isn’t hard to do, but it really pays off! To pre-warm the soil, lay a piece of black plastic mulch on top of the garden bed for two weeks before planting. I usually time it so that I put the plastic out about a week before the last expected frost date.
Once you’re ready to plant you can remove the plastic mulch or leave it in place and cut holes for the slips. If you choose to leave it on the soil, it will continue to keep the plants warm and reduce weed growth. Run a soaker hose underneath the mulch to make watering a snap.
How far apart to plant sweet potatoes
Wondering how far apart to plant sweet potato plants? They should be spaced twelve to eighteen inches apart. If growing them in raised beds, I plant on 18 inch centers. In a traditional in-ground garden, leave three feet between rows to allow room to tend the crop. If you’re short on space, you can also plant sweet potatoes in containers or fabric bags. Just be sure to keep an eye on soil moisture as container dry out quicker than garden beds.
How to grow sweet potatoes
Once your sweet potato slips have been planted in the garden, water them well and continue to irrigate the bed daily for the first week if there has been no rain. After they’ve adapted to their new home, you can reduce watering, but keep in mind that drought-stressed plants yield fewer and smaller sweet potatoes. If you’re not growing them under a black plastic mulch, mulch plants with straw or shredded leaves to reduce the need to water.
Expect the newly planted sweet potato slips to sit for a few weeks as they put on root growth. Once the heat arrives, the vines quickly take off. If the spring weather experiences a setback and cold temperatures are in the forecast, cover your plants with a row cover to insulate them.
While sweet potatoes are generally easy to grow, watch for pests like cucumber beetles, sweet potato weevils, and flea beetles. Wireworms can also be an issue but you don’t notice their damage until harvest time. The larvae of wireworms cause small holes in the tubers. Crop rotation is the best way to reduce insect problems
How to harvest sweet potatoes
Be patient, growing great sweet potatoes takes time. I plant 90 to 100 day cultivars and don’t even bother trying to sneak any tubers before that 90 days has elapsed. Generally the crop is harvested when the vines are blackened by frost. Dig the sweet potatoes with a garden fork, being careful to not skewer your tubers.
How to cure sweet potatoes
Once you’ve harvested all your sweet potatoes, it’s time to cure them. Curing allows the flesh to sweeten up and heals small wounds or cracks on the skin for long-term storage. Proper curing requires warm to hot temperatures and high humidity. If you can, place the tubers where it’s 85 to 90 F with 85% humidity for a week. This can be difficult in a home garden, but I’ve heard of gardeners who use an oven to cure sweet potatoes.
If you only have a small amount of tubers and don’t plan on keeping them more than a few months, quick cure them at 75 to 80 F over one to two weeks. Store cured sweet potatoes in a cool, dark basement where the temperature is around 55 to 60 F.
Did I answer all your questions on how to grow sweet potatoes? If not, leave your questions or comments below.
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