Sweet Potato
Yam, Kumara, Boniato
Tropical plant requiring long, hot summers — plant slips (rooted cuttings) 2–3 weeks after last frost in warm soil. Black plastic mulch is highly recommended to warm soil and suppress weeds. Leaves spread 5–6 ft; give generous space. Harvest before first frost, curing at 85°F and 85% humidity for 1 week to convert starches to sugars and heal skin damage.
- Germination
- 7–14 days
- Harvest after planting
- 90–120 days
- Spacing
- 30–45 cm
When to plant sweet potato
Plant 2–4 weeks after your last spring frost.
Dashed line: typical last spring frost in zone 7 (Apr 5). Zone dates are averages; most of the UK is zone 8–9, central Europe 6–7 and the Baltics and Scandinavia 4–6. In the app, Tomatograph uses your garden's own frost dates.
How to grow sweet potato
- 1
Plant slips
Sweet potatoes grow from rooted shoots called slips, not seed. Plant them 5–8 cm deep and 30–45 cm apart, 2–3 weeks after the last frost, once the soil is at least 18 °C.
- 2
Warm the soil
They need a long, hot summer. Black mulch film warms the soil and keeps weeds down.
- 3
Go easy on feeding
Avoid high-nitrogen fertiliser, which gives lots of vine and few roots. Vines spread 1.5–2 m.
- 4
Harvest and cure
Dig before the first frost, 90–120 days after planting. Cure for about a week somewhere warm and humid to sweeten the roots and heal the skin.
Growing conditions
Light
Full sun
Water
Medium water
Temperature
18–38 °C
Frost tolerance
Frost-sensitive — protect below 0 °C
Days to maturity
90–120 days
How Tomatograph watches your sweet potato
Tomatograph checks your local forecast every morning and only speaks up when one of these applies to your garden.
- Forecast of 2 °C or lowerFrost alert the evening before: cover plants with fleece or bring pots inside.
- 3 days at 35 °C or aboveHeat-wave alert while plants are flowering or fruiting: shade and water early.
- Humidity above 80% for 48 hoursCheck for fusarium wilt, which thrives in those conditions.
- Within a week of maturityHarvest-window reminder based on when you planted.
Sweet Potato questions
- When should I plant sweet potato?
- Plant 2–4 weeks after your last spring frost.
- How long until I can harvest sweet potato?
- About 90–120 days after planting out, depending on variety and weather.
- How far apart should I plant sweet potato?
- Allow 30–45 cm between plants.
- What grows well with sweet potato?
- Good neighbours include thyme, parsnip, dill.
Growing guide written by Tomatograph. Planting figures from openplantdb (CC0 1.0). Zone frost dates are averages from openplantdb (CC0 1.0).