EUGENE, Ore. — When he was 9 years old and riding with his brother on the back of a two-seater tractor on 30 acres in southern California, Gary Jordan planted sweet potatoes one at a time.
“It took us weeks to do,” said Jordan, a Master Gardener volunteer with the Oregon State University Extension Service. “I’ve probably planted more sweet potatoes than anyone you’ll meet. I have great respect for sweet potatoes.”
Jordan graduated from Extension’s Master Gardener Program in Lane County in 2014 and immediately planted a crop of his favorite vegetable. He soon entered a local contest and won first- and second-place awards, which led to giving talks to packed rooms.
“People really want to know how to grow sweet potatoes,” he said.
Why grow sweet potatoes in Oregon?
While many Oregonians assume the climate is too cool, Jordan sees opportunity.
“Everyone says it’s too cold here to grow them,” he said, “but I want to show that’s not true. Sweet potatoes are a super food, one of the most nutritious vegetables.”
Sweet potatoes require significant heat and humidity. Jordan uses clear plastic sheeting to warm soil around the plants, which makes all the difference in the Pacific Northwest. They also need rich, well-draining soil — ideally amended with compost or rotted manure before planting.
If soil is highly fertile, sweet potatoes generally do not require additional fertilizer. Avoid nitrogen-rich fertilizers, which stimulate leaf growth rather than tuber development.
The importance of curing
For maximum sweetness, proper curing is essential.
“The key is curing,” Jordan said. “If you don’t, you don’t get the transition of the starches to sugar.”
Once cured, he prefers baking sweet potatoes whole for flavor and nutritional value — though he enjoys sweet potato fries occasionally.
Jordan also clarifies a common misconception: sweet potatoes and yams are not interchangeable. True yams are unrelated botanically and rarely grown in the United States.
Regional considerations for Oregon gardeners
Sweet potato success varies across Oregon’s diverse climates.
Western Oregon:
- Best region for homegrown sweet potatoes
- Clear plastic mulch is essential for warming soil
- Expect slower growth without supplemental heat
Willamette Valley:
- Warm summer days but cool nights
- Plastic sheeting and sand-filled planting holes boost soil temperatures
- Raised beds offer added warmth and drainage
Oregon Coast:
- Cool, cloudy, humid conditions
- Sweet potatoes benefit from sheltered microclimates against south-facing walls Soil warming with clear plastic is critical
Southern Oregon:
- Warmest, sunniest region for sweet potatoes
- Excellent heat accumulation supports larger yields
- Shade cloth may be needed during extreme heat waves
Central and Eastern Oregon:
- Short frost-free season and large temperature swings
- Transplants (“slips”) should be planted under clear plastic as early as safely possible
- Soil warming and water conservation are key
High-elevation areas:
- Very short season; consider sweet potatoes as experimental crops
- Use black grow bags, plastic mulch and warm irrigation water to maximize heat
Tips for growing sweet potatoes
- Choose an area in full sun.
- Mix about 1 part compost or composted manure into 2 parts soil until fluffy; avoid commercial fertilizer. Mound soil into a slight ridge 12 to 24 inches wide.
- Cover soil with clear plastic pulled smooth and tight; secure edges well with bricks, wood, U-shaped staples or rebar laid flat.
- Warm the soil to about 80 degrees; use a soil or compost thermometer. Do not worry about overheating — sweet potatoes thrive above 100 degrees.
- Make slits in the plastic about 15 inches apart. Pull back each slit to create a 12-by-12-inch hole and form a small depression. Plant slips into the depression.
- Fill planting holes with construction sand for drainage and heat retention.
- Water late in the day when soil is warmest. Ideally, use a soaker hose under the plastic and water warmed in the sun.
- Harvest carefully in fall when temperatures drop into the 60s; avoid bruising or scratching the tubers.
- Cure sweet potatoes immediately in a warm, humid spot — 85 to 90 degrees — for five to seven days. A greenhouse or small heated room with a humidifier works well.
Previously titled OSU Extension Master Gardener goes sweet on potatoes
