Sweet potatoes are a summer crop with a tropical soul: they love heat, they love sun, and they repay a long hot season with a harvest of sweet, orange-fleshed roots that store for months. They are also one of the prettiest vegetables to grow, with trailing vines that cover the ground in heart-shaped leaves.
They take 90–120 days to mature and they are tender — a single frost kills the vines — so they are a crop for warm gardens and long summers. Give them heat, loose soil and room to run, and they will do the rest.
Sweet Potatoes at a glance
| Growing factor | What sweet potatoes need |
|---|---|
| Sun | full sun |
| Soil pH | 5.5–6.5 |
| Days to germination | 14–21 |
| Days to maturity | 90–120 |
| Spacing | 12–18 inches |
| Water needs | moderate |
| Cold tolerance | tender |
| Family | Convolvulaceae |
Starting seeds
Sweet Potatoes are started indoors and moved outside as seedlings. Sow indoors in trays or cells, keep the mix moist but not wet, and expect germination in 14–21 days. Give seedlings strong light from the moment they emerge — a bright windowsill is rarely enough, so a grow light a few inches above the leaves is worth having.
Start seed early enough that seedlings are sturdy by planting-out time, but not so early that they outgrow their pots and go leggy indoors. Work backwards from your last frost using our seed-starting calculator and the frost-date calculator, and confirm the timing with your local extension service — Zones 11–13 are frost-free, so the calendar there is about heat and rain rather than frost.
Sweet potatoes are not grown from seed: they are grown from slips, which are shoots sprouted from a stored root. Start slips indoors 6–8 weeks before your last frost by half-burying a sweet potato in damp compost or suspending it in water, then snap the shoots off once they are a few inches tall and root them in water or compost. Germination of the shoots takes 14–21 days in warm conditions. In Zones 3–6 start slips indoors early and plant out only when the soil is warm; in Zones 7–9 plant in late spring; in frost-free Zones 11–13 plant in spring and grow them year-round.
Transplanting and planting out
Plant slips out only when the soil is thoroughly warm and all danger of frost has passed — sweet potatoes sulk in cold soil and a late frost kills them outright. Space slips 12–18 inches apart in rows, and set them deep, burying the stem up to the top leaves so roots form along the buried stem. Water them in well and mulch immediately. In short-season zones, growing under black plastic or in a raised bed warms the soil and buys you the extra weeks this crop needs.
When you set plants out, space them 12–18 inches apart — that spacing is what the mature plant needs, and crowding is one of the commonest causes of small harvests. Our plant-spacing calculator works out how many plants fit your bed, and the square-foot garden planner can lay the bed out for you. Harden seedlings off for a week before planting out, moving them outside for longer each day, and plant on a cloudy day or in the evening so they do not wilt in their first hours outdoors.
Soil and feeding
Sweet potatoes want loose, sandy, well-drained soil at pH 5.5–6.5 — they tolerate slightly acid soil better than most vegetables. Heavy clay is the enemy: it gives misshapen, cracked roots, so add compost and sand to lighten it, or grow in a raised bed. They are light feeders, so do not over-fertilise — too much nitrogen gives a jungle of vines and tiny roots. A little compost at planting time is enough.
Aim for a soil pH of 5.5–6.5 — a simple soil test will tell you where you stand, and garden lime or sulfur can nudge pH up or down over a season. Feed lightly and steadily rather than in one heavy dose: too much fast nitrogen late in the season pushes leafy growth at the expense of the part you eat. Our fertiliser calculator works out amounts for your bed size, and the raised-bed soil calculator and soil-volume calculator tell you how much mix a new bed needs. A mulch layer after planting keeps the soil moist and cool and feeds the soil as it breaks down.
Watering
Water needs are moderate: keep the soil evenly moist through the growing season, watering deeply when the top inch or two dries out. Deep, infrequent watering builds deeper roots than a daily sprinkle, and it keeps the plants steady through dry spells.
Water needs are moderate: sweet potatoes need regular water while the slips establish and the roots begin to form, but once the vines are running they are fairly drought-tolerant. Water deeply in dry spells, and stop watering two to three weeks before harvest — dry soil at the end gives better-flavoured roots and makes curing easier. Avoid wetting the leaves, which invites disease, and never let the bed sit waterlogged.
Water at the base of the plant, in the morning, so the leaves dry quickly and the water reaches the roots instead of evaporating off the surface. A soaker hose or drip line is ideal. Our watering calculator gives a starting point for your bed size and soil, and the watering schedule generator can build a routine around it. Mulch is your best friend here: a few inches of straw or shredded leaves cuts evaporation and keeps moisture even between waterings.
Sunlight and temperature
Sweet potatoes need full sun — the hottest, sunniest spot you have — and a long, warm season. They are tender, so frost is fatal to the vines, and cool summers give a poor harvest. In Zones 8–10 they thrive; in Zones 5–7 they need the warmest site and a head start indoors; in frost-free Zones 11–13 they grow all year. Black plastic mulch warms the soil and is worth using in any zone with a short summer.
This crop is rated tender for cold tolerance, so plan your season around that: hardy and frost-tolerant crops can be sown and harvested around frosts, while tender crops need warm soil and frost-free nights. Our sunlight calculator can check whether your spot gets enough sun through the season, and the hardiness-zone finder will confirm your zone. If your summers run very hot, afternoon shade or a shade cloth can keep a cool-season crop productive for a few extra weeks.
Pests and diseases
Sweet potatoes are fairly pest-free in most gardens, but a few insects find the vines. The ones to expect are aphids, slugs and cutworms.
- Aphids — cluster on young shoots in spring. Wash them off with water and encourage ladybirds.
- Slugs — chew young slips and leaves in damp weather. Protect newly planted slips and pick slugs off at dusk.
- Cutworms — cut young slips at soil level overnight. Use cardboard collars around slips and check the soil at the base of damaged plants.
Inspect plants weekly, especially the undersides of leaves, and act early — a small problem caught in time is a hand-picked handful of pests, while a late one can cost the crop. Row cover keeps many flying pests off young plants, and healthy, well-watered plants resist attack far better than stressed ones. If you need help identifying what you are seeing, our pest-identifier helper and plant-disease checker walk through the symptoms.
Companion plants
Sweet potatoes pair well with marigolds, basil, onions and lettuce, though the vines spread so widely that companions are best planted at the edges of the bed. Marigolds help keep soil pests down, and the dense vine canopy smothers weeds once it closes over — one of the crop's great virtues. Keep them away from other root crops, which compete for the same ground.
Good companions for sweet potatoes include:
- Marigolds
- Basil
- Onions
- Lettuce
Our companion-planting finder can suggest more pairings for your bed plan. As a general rule, avoid planting members of the same family (Convolvulaceae) in the same spot year after year — rotate beds so soil-borne problems do not build up.
Harvesting
Harvest before the first frost, from about 90 days after planting, once the leaves start to yellow. Dig carefully with a fork, well away from the plant, because the roots are delicate and bruise easily — a bruised sweet potato will not store. Cure the roots for 10–14 days in a warm, humid place (around 80°F if you can manage it) so the skins toughen and the starches turn to sugar; uncured sweet potatoes taste starchy and bland. After curing, store them in a cool, dry place — never in the fridge, which damages them.
Expect the crop to be ready about 90–120 days after sowing, though weather and variety shift that window by a week or two either way. Our harvest-date calculator works out your expected harvest date from your sowing date, and the vegetable-yield estimator can estimate how much a bed should produce. Harvest in the morning when plants are cool and crisp, and use a sharp knife or secateurs rather than tearing, which damages the plant and invites disease.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Lots of vine, few roots | too much nitrogen or too little sun | Don't overfeed; give them the sunniest spot. |
| Small roots | a short or cool season | Start slips early; warm the soil with black plastic. |
| Cracked or misshapen roots | heavy clay soil or uneven watering | Grow in loose, sandy soil or a raised bed. |
Lots of vine, few roots
Likely cause: too much nitrogen or too little sun Sweet potatoes respond to rich soil by growing vines instead of roots. Skip the fertiliser, give them full sun, and be patient — the roots bulk up late in the season.
Small roots
Likely cause: a short or cool season Small roots usually mean the season was too short or too cool. Start slips indoors, plant into warm soil, and use black plastic mulch to add heat in short-season zones.
Cracked or misshapen roots
Likely cause: heavy clay soil or uneven watering Roots crack when they hit compacted soil or when a drought is followed by heavy rain. Loosen the soil deeply before planting and water evenly through the season.
Frequently asked questions
What is a sweet potato slip?
A shoot sprouted from a stored sweet potato root. You snap the shoots off, root them in water or compost, and plant them out. Sweet potatoes are not grown from seed.
When do I harvest sweet potatoes?
Before the first frost, about 90–120 days after planting, once the leaves yellow. Dig carefully — the roots bruise easily and bruised roots won't store.
Why do sweet potatoes need curing?
Curing — 10–14 days in a warm, humid place — toughens the skin and converts starches to sugars. Uncured sweet potatoes taste starchy and bland and don't keep.
Can I grow sweet potatoes in a container?
Yes, in a large container or grow bag with loose compost — the vines will trail over the sides. One plant per large bag is about right.
Why are my sweet potatoes small?
Usually a short or cool season, or too much nitrogen pushing vine growth. Start slips early, warm the soil, and don't overfeed.