Learning how to grow sweet potatoes successfully comes down to understanding how sweet potatoes grow. This crop is in the morning glory family - a vining, often tenacious plant, that is a well-known weed in many gardens. Sweet potatoes, while related, won’t become a nuisance in the way that morning glories can be. But they are a tenacious vine that loves to spread under full sun. They’ll run wild without a hand from you, but there are a few things you can keep in mind if you want to harvest a hefty bunch of tubers! Follow these simple steps to get larger tubers, higher yields, and healthy, beautiful vines.

How to Grow Sweet Potatoes

Just like with any other crop, you’ll need to understand the timing and resource needs of sweet potatoes in order to grow them successfully.

When to Plant Sweet Potatoes

Sweet potatoes are a warm season crop and want to be planted, not only after the last frost, but after the soil has warmed up a bit. This means, in most growing zones, you want to wait at least three weeks after your last frost, in some zones, even up to six weeks, before you plant your sweet potato slips outdoors. You’re looking for the soil to have warmed to at least 65°F before you plant your slips.

In Northern and colder gardens, this looks like waiting to plant out your sweet potato slips until mid-June. For Southern gardens, sweet potatoes can typically be planted between mid-May and mid-June.

Best Soil for Growing Sweet Potatoes

Like other root crops, sweet potatoes have a great preference for loose, loamy soils. Loose soil that is free of clay and rocks allow the tubers to expand uninhibited, which can result in higher yields. However, amending and aerating your clay soils can help greatly. Sweet potatoes also prefer well-draining soils, like sandy soil. To achieve this in non-sandy soiled environments, you can mix sand into your beds or grow your sweet potatoes in raised beds which naturally have better drainage! Sweet potatoes do not like nitrogen-heavy soils. Too much nitrogen will result in a lush field of sweet potato vines and almost no tubers.

Sweet Potato Spacing and Growing Requirements

Making sure your slips are appropriately spaced is the first line of defense for ensuring that tubers can mature to their optimum size. Slips must be planted at least three inches deep, 12 inches apart, and rows three to four feet apart. This ensures there’s enough room for these plants to spread out both below and above ground!

Overcrowding any plants leads to multiple plants competing for the same available water, nutrients, and sunlight, which often results in just a lot of stunted, poorly developed plants, regardless of the space that has been saved. Not to mention, planting too close together means that diseases spread more easily among crops and fungal issues can run amok!

How to Water Sweet Potatoes Properly

Sweet potatoes need quite a bit of water throughout the season to develop to a hefty size. This is especially true as the slips are getting established early on. When you plant your sweet potato slips, take care to water deeply and regularly, keeping the soil consistently moist. Slips can often exhibit signs of transplant shock when they’re planted - this is completely normal. These resilient plants will bounce back with some hefty watering in the first few weeks! Assuming your soil has good drainage, you won’t have to worry about rot. Once established, sweet potatoes will appreciate consistent moisture as well. Create a schedule to water your growing sweet potatoes. They’ll prefer a long, deep watering every other day, or every few days, rather than a short watering daily. Ensuring the soil stays moist deep into the ground encourages a strong root system, which supports tuber development! Mulching sweet potatoes does a two-fold favor: helping to prevent weed growth and competition, as well as keeping moisture in the ground. And finally, after a long, hot summer of watering your sweet potatoes, stop watering for three to four weeks before you’re expecting to harvest. This allows the sweet potatoes to mature and makes the curing process simpler once harvested.

How to Increase Sweet Potato Size and Yield

Following the planting instructions for sweet potato slips is a great way to start off when you’re going for BIG sweet potatoes. But, if that’s not enough, here are a few details to keep in mind.

Dig Deep

Starting with well prepped soil can result in a very respectable harvest with very little work after planting. When amending your soil, especially in very heavy, clay-filled gardens, dig down 18 inches deep to really mix in your organic matter and sand. You could also consider growing in raised beds, which offer plenty of height and loose soil to grow in. On top of that, you can even create mounds on top of the soil so that there’s even more depth! The more underground space your sweet potatoes have to grow, the stronger they’ll be.

Don’t Plant Too Early

Once you’ve had your soil all loosened and prepped, don’t spoil the fun by planting too early. Sweet potatoes really take off when the soil is warm. They’re native to Central and South America and have a zero tolerance policy for cold temperatures. Wait to plant out your slips until the soil has reached 65°F. Soil can heat up pretty slowly in the spring time as it tends to hold onto those cooler winter temperatures. This process can be sped up in the spring by covering your planting area in black plastic for a few weeks before your last frost date. The black plastic holds in heat and keeps temperatures warmer, moving your planting date up! This is especially helpful in Northern climates where the growing season can be relatively short, as sweet potatoes take between 90 and 120 days to mature.

Water is Essential

The first two weeks after planting your slips are crucial for getting established. It is so important to keep your slips well-watered during this time to ensure their survival! Throughout the season, try not to let the soil dry out too much. We recommend doing multiple long, deep waterings per week rather than a daily shorter water.

Keep Those Vines in Check

Just like their brethren, morning glories, sweet potatoes are a vining plant. These enthusiastic spreaders will quickly take over their allotted space and beyond. This can make a great living mulch, keeping weeds at bay and the soil moist, but in order to grow big sweet potatoes, you need to keep these vines in check. The sweet potato is inclined to spread above ground, as this is how they spread underground - rerooted as they move along your garden. However, this results in a wide swatch of tiny tubers and root systems all over your garden. To harness that energy into a harvest, keep the vines clipped back within three feet of the main plant. Keeping them regularly pruned means bigger, and also easier, harvests. Not to mention, the vines are edible! As you’re snipping them back, keep them to stir fry with some other veggies later on.

Use the Right Fertilizer

Sweet potatoes are the crop that made us firm believers in having one’s soil tested as a part of a pre-season prep plan. We kept hearing stories of folks that would have great harvests of huge tubers one year and then the next year stunning above ground vines, but then when they’d harvest all they’d find are scrawny little tubers. The culprit? Too much nitrogen in the soil in year two! High levels of nitrogen in the soil, occurring either naturally, or more likely through things you are adding to the soil, will result in a luscious flush of foliage with almost no root, flower, or fruit development for any crop, and sweet potatoes aren’t immune! When selecting a fertilizer for your sweet potatoes, choose one that is higher in phosphorus and potassium than nitrogen. We love bone meal and kelp meal for our sweet potatoes! Don’t over-fertilize! Sweet potatoes are not heavy feeders, so these should just be an occasional snack if your soil is less than ideal.

Growing Sweet Potatoes in Containers

Growing sweet potatoes in containers or raised beds is probably the best way to ensure good drainage in clay or heavy-soiled gardens. When growing sweet potatoes in containers, be sure to use containers that are large and deep, ideally 15 to 20 gallons and at least 12 inches deep. If there aren’t holes already, you’ll need to drill holes at the bottom of your container for drainage. We especially love the 20 gallon Dirt Pot containers which are reusable and offer great drainage.

How Long Do Sweet Potatoes Take to Grow?

Sweet potatoes are a tropical crop and require a long growing season to mature. It depends on the variety, but typically sweet potatoes will take between 90 and 120 days to grow! You can allow your sweet potatoes to mature until your first frost date, harvesting them before the frost. If you have to harvest before the 90-120 day mark, you will still get tubers, they just may be small. When at all possible, we recommend waiting the full 90 to 120 days!

Common Problems When Growing Sweet Potatoes

Just like any crop, sweet potatoes have their own range of pests, diseases, and growing issues.

Slips Dying After Planting

If slips don’t receive the right treatment, they can easily die back due to lack of water or trouble establishing. This is why the work you do right after you plant them can make or break your harvest. Slips need to be planted deep; up to the first leaves. This is because the roots form from the stem of the slip, similar to how tomatoes grow. The deeper you’re able to plant them, the more roots can sprout from the buried stem. Watering at this stage is also incredibly important. Slips can start to show signs of stress pretty immediately. The goal of watering your slips is not to avoid these signs of stress (they’ll likely be droopy for a while no matter what you do), but to not let this droop trick you into giving up. While their aerial parts are looking sad, all that watering you’re doing is making the underground roots go wild! As soon as that root system is established, you’ll see the tops perk right back up.

Fungal Diseases

Fusarium Wilt and Leaf Spot are common fungal diseases that can plague your sweet potatoes. Fusarium Wilt affects the vascular tissues of the plant which causes yellowing leaves that wilt and droop and ultimately stunts their growth. This disease can live in the soil and is also carried by cucumber beetles. For this reason, we don’t recommend planting your sweet potatoes in a bed that had cucumbers growing in it for the past couple of years! Leaf Spot is waterborne and can cause irregular patterns on leaves that may turn yellow and crisp. While these fungal diseases are not treatable with fungicide, if you practice good garden hygiene, avoid getting foliage wet late in the day, and prune off infected leaves and stems, you can mitigate the effects of these issues.

Flea Beatles

Flea beetles are tiny, black bugs that eat small holes in the leaves of seedlings. They’re especially common amongst nightshade crops. You’ll know you have a flea beetle problem if you have chewed up leaves and run your hand through them and you see a bunch of little black beetles jump from the leaves just like fleas! They’re aptly named and can affect the crop’s ability to photosynthesis. The damage is far less catastrophic if you can protect your seedlings until they’re established. We recommend covering your sweet potato slips with row cover until your crop is established to protect them from this pest, especially if it is common in your garden. You can also use a trap crop, like fast-maturing radishes, to attract flea beetles while your sweet potato slips are getting established under row cover. Once infected, remove the radishes and pests and dispose of them in the garbage, not the compost. This will help keep populations low!

Root-Knot Nematode

Root-knot nematodes are microscopic insects that affect a whole range of crops. While really severe infections can cause above-ground affects, mostly the effects are seen in the roots of plants, which aren’t typically found until harvest. Root-knot nematodes cause galls to form on the roots. Brown, bumpy, or cork-like lesions can form on the skin and the flesh can be dark colored or woody when cut open. These lesions can cause storage issues, allowing pathogens to enter the wounds, and also make the sweet potatoes unmarketable. Many nematode species tend to be common in the sandy, loamy soils that sweet potatoes thrive in, so treatment is necessary before planting in that location again. We recommend growing a cover crop of nematocidal marigolds and then solarizing the area to kill back nematode populations.

When and How to Harvest Sweet Potatoes

Three to four months have gone by, the first frost is rapidly approaching (in many growing zones), and it’s time to harvest your sweet potatoes! Your best bet is to mark your calendar with the recommended harvest date for your variety and harvest then. In some zones, this might be a game of just harvesting them before your first frost. In others, with milder climates, you definitely want to keep an eye on the calendar so that your roots are harvested at the perfect size. In these longer-season climates, you may see the vines start to yellow, starting at the soil level. This is a sign that it’s about time to harvest. But, don’t wait for the aerial parts to die back entirely as you would with Irish potatoes!

To harvest your sweet potatoes, start by cutting back the vines to the crown of the plant. Use a garden fork or shovel and insert it into the soil about ten inches away from the crown of the plant. Once inserted all the way, push the handle towards the ground which will lift up and loosen the soil around the tubers. Take care not to stab or scratch the sweet potatoes, as this can affect curing. Find the tubers in the soil and dust them off. Do not wash the tubers with water, it’s okay if there is some dirt on them!

Curing Sweet Potatoes

The curing process helps the starches in the tubers convert to sugar. This makes them tastier and also helps with longterm storage! For the home gardener, curing your sweet potatoes can look like keeping them on a porch or other covered location for a week or two. If it’s early enough in the fall, this can be outside where it is relatively warm and humid still. If it’s cooled off by the time you harvest, you’ll want to choose a spot inside that is relatively warm and at a high humidity, around 85 to 90%. Keeping them on a screen in a single layer is best, as this allows airflow to reach all sides of the root. After this process, they can be stored in a cool, dry place, like a basement, and kept through the winter in boxes or baskets and wrapped in newspaper.

Quick Tips for Growing Big Sweet Potatoes

Amend your soil at least 12 inches down into the soil ahead of planting. This will give your tubers plenty of room to develop to their full size potential.
Wait to plant until the soil is nice and warm - at least 65°F.
Water very well as your sweet potato slips are getting established, and ensure the soil stays evenly moist throughout the crop’s maturation process.
Keep the vines clipped back to no more than three feet from the crown of the plant. This ensures energy will be cycled into tuber development, rather than foliage development.
Don’t apply a fertilizer with too much nitrogen and focus on phosphorus and potassium content instead.

Sweet Potato Growing FAQs

Still got questions? We’ve got answers.

How deep do sweet potatoes grow?

Sweet potato tubers can reach 12 inches underground. This is why it’s important to amend your soil to that depth.

Can you grow sweet potatoes from store-bought ones?

In theory, yes! Organic sweet potatoes can sprout slips while non-organic sweet potatoes are sometimes treated to not sprout slips and may not perform. However, we do not recommend doing this. This is a really easy way to introduce new pathogens into your garden that can harm not only your sweet potato crop, but other crops in your garden. Buying your slips from a trusted source, or sprouting them from your own sweet potatoes from last year’s harvest is the safest way to grow sweet potatoes and keep your garden healthy.

How many sweet potatoes per plant?

Your yield per plant of sweet potatoes can vary widely depending on soil quality and fertilizer used. Typically, however, you can expect to harvest between four and six sweet potatoes per plant.

Do sweet potatoes need full sun?

Yes! Sweet potatoes need full sun in order to produce to their fullest potential. This means at least eight hours of uninterrupted sunlight.

Ready to get growing? Check out our wide variety of sweet potato slips to grow this season. There’s sure to be one that satisfies your sweet (potato) tooth!

	*Article Written by: Hannah Gibbons*
	About the Author: Hannah Gibbons, an employee at Sow True Seed since 2020, has over a decade of experience in the agricultural industry. Their passion for environmental education and regenerative agriculture has been the cornerstone of their work, aimed at making gardening accessible to all.