Grow sweet potatoes in the ground by planting certified slips 12–18 inches apart in warm, sandy-loam ridges, then curing the harvest for 10 days to lock in flavor and storage life.
The difference between a good sweet potato crop and a disappointing one almost always comes down to two things: soil temperature at planting time and the curing step after harvest. Plant too early in cold ground and the slips simply sit there. Skip the curing step and your potatoes come out bland and rot within weeks. Here is how to do both right, along with everything else that matters for a solid in-ground crop.
What Is the Best Soil and Bed Preparation for Sweet Potatoes?
Sandy loam with a pH between 5.8 and 6.0 is the ideal home for sweet potatoes. The soil needs to be loose enough for the roots to swell into full-size tubers—heavy clay or compacted ground produces gnarly, undersized potatoes unless you amend it heavily with compost or aged manure.
Build raised ridges about 8 to 10 inches tall and space them 36 to 42 inches apart. The ridges warm faster in spring, drain excess water, and give the developing roots more soft soil to expand into. Before forming the ridges, work in a couple of inches of compost and a continuous-release fertilizer with a 1-2-2 ratio such as Miracle-Gro Performance Organics Edibles granules. Avoid high-nitrogen mixes; those produce monster vines and puny roots.
When Should You Plant Sweet Potato Slips in the Ground?
The ground needs to be at least 65 degrees Fahrenheit, and 70 is better. That usually falls two to four weeks after your last spring frost. In zones 7 through 10 you can plant one month after frost; in cooler zones like Wisconsin or Colorado you may need to wait until late May or early June and still pick a fast-maturing variety to beat the first fall frost.
If you are gardening in a region with short, cool summers, warm the soil ahead of time by covering the planting area with black plastic or landscape fabric for three weeks before you intend to plant. Row covers after planting can also trap heat and extend the warm window.
Where Do You Get Sweet Potato Slips, and Can You Grow Your Own?
Certified slips are the cleanest starting point because they come disease-free. You can order them from seed catalogs or grow your own from a store-bought sweet potato using one of three methods.
Mason jar method. Stick toothpicks around the middle of a sweet potato, suspend it cut-side-down over a jar of water, and put it in a sunny window or under a grow light. Change the water every few days. Slips will appear in a few weeks. Start this three months before your planting date.
Whole-potato soil method. Bury a whole sweet potato in a bin or nursery flat so the bottom half is covered and the top is exposed. Keep the soil moist but not soggy. Optional: cover loosely with plastic to hold humidity.
Cut-root flat method (recommended by University of Maryland Extension). Fill a flat with 1 to 2 inches of coarse sand or soilless mix. Slice a sweet potato lengthwise, place the cut side down on the sand, and cover with another 2 inches of sand. Keep it warm (75 to 85 degrees) and moist with plastic draped over the top until shoots emerge. Then remove the plastic and give the sprouts 14 to 16 hours of light per day on a timer. Pull the slips when they are about 6 inches long and have a few leaves.
Whichever method you use, the slips come out rootless when you pull them. Keep them well watered for the first week or two after transplanting or they will wilt and die.
How to Plant Sweet Potato Slips: Spacing, Depth, and the Big Mistakes
Plant slips 2 to 3 inches deep, leaving the leaves and the growing tip above the soil line. Space them 12 to 18 inches apart along the ridge. Burying them deeper than a few inches or planting whole tubers in the ground instead of slips are two of the most common mistakes—both slow the plant down and cut the yield.
Water the slips in well after planting. For the next week or two, keep the soil around each slip consistently moist so the roots can establish. After that, switch to a deep weekly soak. During a serious drought, give them an extra deep watering. And keep an eye on the foliage: if the leaves look pale or yellow, the bed probably needs more potassium—side-dress with a low-nitrogen fertilizer before August.
One Planted Slip = How Many Sweet Potatoes?
Expect 3 to 5 pounds of sweet potatoes per slip under good conditions. Plenty of sun, loose soil, and consistent water push that number upward; crowded spacing or nitrogen overload pulls it down.
| Growth Factor | Ideal Condition | What Hurts Yield |
|---|---|---|
| Sunlight | 8–10 hours full sun | Shade or partial sun |
| Soil pH | 5.8–6.0 | Above 6.8 or below 5.5 |
| Soil Temp at Planting | 65–70°F | Below 60°F |
| Nitrogen Level | Low to moderate (1-2-2 ratio) | High nitrogen (lush vines, small roots) |
| Days to Maturity | 85–120 days | Frost before maturity |
| Watering | Weekly deep soak, more during drought | Waterlogged soil or long dry spells |
| Spacing | 12–18 in between plants, 36–42 in between rows | Overcrowding (small tubers, disease) |
When and How Do You Harvest Sweet Potatoes?
Watch the vine ends. When they start to turn yellow, the potatoes are at their peak. You can also check by gently digging around the base of one plant to see the size of the tubers. Plan to dig them all up before the first fall frost—cold soil damages the roots and ruins storage quality.
Use a digging fork to loosen the soil in an 18-inch circle around each plant, then pull the potatoes out by hand. Sweet potatoes bruise easily; do not drop or toss them into a bucket, and handle them like eggs until they have cured.
The University of Maryland Extension guide describes the full process and covers soil prep and pest management for home growers.
Why Do You Cure Sweet Potatoes, and How Do You Do It Right?
Curing converts starches into sugars, heals scratches in the skin, and gives the potatoes the sweet flavor and long shelf life you expect from a good grocery-store sweet potato—without it, the roots taste bland and start rotting within weeks.
Set your harvested, unwashed sweet potatoes in a warm, humid spot—80 to 90 degrees Fahrenheit with around 80 percent humidity—for 10 days. A basement corner near a furnace, an enclosed porch, or a seed-starting tray with a humidity dome all work. Cured potatoes feel hard to the touch, unlike the semi-flexible feel of a fresh one. After curing, store them in a cool (55 to 60 degrees), dark place and they will keep for months.
Sweet Potato Harvest and Storage Checklist
This is the exact sequence that produces a sweet, long-lasting crop.
- Dig gently with a fork 18 inches around the plant.
- Pull by hand; brush off loose dirt, do not wash.
- Inspect immediately: set aside any cut or badly bruised potatoes for the kitchen, keep undamaged ones for storage.
- Cure at 80–90°F with 80% humidity for 10 days.
- Store cured potatoes at 55–60°F in a dark, ventilated spot.
- Check stored potatoes every couple of weeks; remove any that soften or sprout.
Choosing the right soil is the single most reliable way to boost yield before a single slip goes in the ground. Our tested roundup of the best soil for sweet potatoes covers bagged mixes and amendments that match the sandy-loam pH sweet potatoes need.
FAQs
Can you just put a whole sweet potato in the ground?
Planting a whole sweet potato directly in the ground rarely works well. The plant wastes energy on the mother tuber instead of setting new roots, and the yield is low. Starting slips first gives you a much stronger, more productive crop.
How deep should sweet potato ridges be?
Raise the planting ridges about 8 to 10 inches tall and flatten the top slightly. The ridge keeps the developing tubers above standing water and helps the soil warm faster, which is essential for growth in cooler climates.
When is the latest you can plant sweet potatoes?
You need at least 85 days of frost-free weather after planting, preferably 100 to 120 for full-size tubers. Count backward from your average first fall frost date and do not plant any later than that window allows.
Do sweet potatoes need full sun?
Yes, 8 to 10 hours of direct sunlight each day is the minimum for decent root development. Anything less than 8 hours cuts the yield noticeably and produces smaller, thinner potatoes.
How do you store sweet potatoes after harvest?
After curing, keep them in a dark spot at 55 to 60 degrees Fahrenheit with good airflow. A basement or a cool pantry works. Do not refrigerate raw sweet potatoes—cold turns their starch to sugar faster and ruins the texture.
References & Sources
- University of Maryland Extension. “Growing Sweet Potatoes in a Home Garden.” Covers soil preparation, slip starting, planting depth, and pest management for home growers.
- Bonnie Plants. “How to Grow Sweet Potatoes.” Details on spacing, watering, and harvesting from a major plant supplier.
- Oklahoma State University Extension. “Sweet Potato Production.” Commercial-grade guide on soil pH, curing, and storage requirements.
- Fine Gardening. “How to Grow Sweet Potatoes.” Practical advice on soil prep and avoiding high-nitrogen fertilizers.