Sweet potato (Ipomoea batatas) is one of the most productive crops a warm-climate garden can carry. A single planting tuber can produce a handful of slips, each slip becomes a sprawling vine, and each vine can set several good sized tubers underground. Both the roots and the young leaves are eaten.
Sweet potatoes need warmth from the day the slips go in until the day the tubers come out, so timing matters more than technique. This guide covers the whole season, from the tuber that arrives in the post to the crate in the shed.
What are you actually planting?
You plant slips, which are the leafy shoots that a sweet potato tuber sends up when it is kept warm and moist. The tuber is the nursery, not the crop.
Our tubers are first generation foundation seed from an Australian specialist sweet potato seed grower. They are supplied clean, with no post-harvest treatments, so they shoot readily. Supermarket sweet potatoes are handled for the shelf, not the garden: they are cured and held in cool storage to keep sprouting down, so they can be slow and unreliable to shoot, and they can carry viruses that cut yield when they are replanted. Starting from clean planting stock gives the crop the best start.
On appearance: our grower notes that some of this season's tubers carry a light bronze tint on the skin from being grown through winter in cold ground, and the purple in a purple-fleshed variety varies from tuber to tuber. Neither affects how well the tuber shoots or what it grows.
How do you sprout the slips?
Sit the tuber half-buried in a tray of moist potting mix, or suspend it in a jar of water, and keep it warm and bright. Shoots usually appear within two to four weeks, and they are ready to cut once they are 15 to 20 cm long. Allow four to six weeks from starting the tuber to having rooted slips ready to plant.
The tray method is the more reliable of the two because the shoots root into the mix as they grow. The jar method is slower but works well on a sunny kitchen windowsill. Either way, snip or twist the slips off at the base and stand them in a glass of water for a few days until white roots appear. Then they are ready for the garden.
For the full method, including how many slips to expect and how to keep a tuber producing for weeks, see our guide to sprouting sweet potato slips.
When should you plant?
Plant slips out only after all danger of frost has passed and the soil has warmed, because sweet potato is frost tender from tip to root. In most temperate gardens that means October to December. In the subtropics the window opens in September and runs into summer, and in the tropics the plant can go in most of the year, with mounded beds the usual answer to wet-season rot.
Cool districts such as the New South Wales tablelands, central Victoria and the Tasmanian highlands are marginal. A warm, sheltered, north-facing bed planted in November can still produce a worthwhile crop, though the tubers are often smaller. Our zone by zone planting calendar covers each region in detail, including Perth and southern WA.
How do you prepare the bed?
Choose the sunniest spot you have, and loosen the soil deeply so the tubers can swell evenly. Sweet potatoes like a loose, well drained, sandy loam with some compost worked through. Heavy clay tends to give long, thin, misshapen roots, so on clay it is worth building a raised mound or ridge about 20 to 30 cm high and planting into that.
Go easy on nitrogen. A bed that was well manured for the previous crop is ideal, but fresh manure or a high-nitrogen feed at planting pushes the plant into leaf at the expense of tubers. If the soil is poor, a light dressing of a balanced organic fertiliser or a potassium-rich feed such as sulphate of potash is enough.
How do you plant the slips?
Bury the lower two thirds of each slip, laying it at a slant so several leaf nodes sit under the soil, and water it in well. Tubers form at those buried nodes, so a slip planted deep and on an angle usually out-yields one planted upright.
- Space slips 30 to 40 cm apart along the row.
- Leave 75 cm to 1 m between rows, because the vines will cover every gap.
- Plant in the late afternoon, and water daily for the first week while the slips settle.
Some slips wilt for a day or two after planting and then recover. A slip that has not recovered after a week can be replaced.
How do you look after the vines?
Water deeply about once a week in dry weather and keep the bed mulched. Once established, sweet potatoes need less attention than most summer crops.
One job is worth doing: lift the vines every few weeks. Where a vine touches bare soil it can root and start small extra tubers at that spot, which reduces the main crop. Lifting the runners gently off the ground, or laying a light mulch under them, keeps the plant feeding the tubers under the main crown.
Pinch the young shoot tips for the kitchen whenever you like. They cook like spinach, and our sweet potato recipes include a garlic leaf stir-fry. A light picking costs the crop very little, though stripping the vines hard will cut the tuber yield. Around midsummer the vines may produce pale pink trumpet flowers, because the plant is a member of the morning glory family.
What goes wrong?
Sweet potato weevil (Cylas formicarius) is the main pest to know about in Queensland, the Northern Territory and far northern New South Wales, where its larvae tunnel into tubers and spoil them. Damage is worst in hot, dry spells, because the weevil reaches the tubers through cracks in dry soil, so steady water and a good mulch are part of the defence. There is no home garden treatment, so the rest is cultural: rotate beds, never replant old or damaged tubers, clear every scrap of crop residue at harvest, and remove wild morning glory vines nearby.
Elsewhere the common problems are grasshoppers chewing leaves, which the plant tolerates, and rot in waterlogged soil, which it does not.
When and how do you harvest?
Start lifting about four to five months after planting, once the leaves begin to yellow, and in any case before the first frost blackens the vines. Warm districts are often ready at four months. Cool districts usually need the full five.
Cut the vines back, then work in from the edge of the bed with a fork, lifting gently, because the skins bruise and scratch easily at harvest. Brush the soil off rather than washing it. Tubers around 15 to 20 cm long are usually the best eating, and very large ones can be woody in the middle.
How do you cure and store them?
Cure the tubers for one to two weeks somewhere warm, humid and airy, such as a shaded verandah or a warm shed, before storing them. Curing heals harvest scratches, thickens the skin and converts some starch to sugar, which is why a cured sweet potato tastes sweeter than one straight out of the ground.
After curing, store them in a cool, dark place with good airflow, never in the fridge. Very dry air makes them shrivel, so a pantry suits them better than a heated room. Well cured tubers can keep for several months. Keep the best few tubers aside if you want to sprout your own slips next season.
You can find our foundation seed tubers in the sweet potato tuber collection, and if you are still deciding between varieties, our comparison of Beauregard, Eclipse and Northern Star will help. For the rest of the spring sowing list, see the Australian Sowing Almanac.
Due to quarantine restrictions and our shipping policy, we cannot send sweet potato tubers to Western Australia or Tasmania. Interstate plant movement rules are set by each state, and our shipping information page explains how we apply them.
Get the tubers
First generation foundation seed tubers from an Australian specialist grower, supplied clean for sprouting your own slips. Packs of 2, 4 or 10 tubers, all in our sweet potato tuber collection.
Sweet Potato - Beauregard TubersOrange flesh, rose gold skin. The productive all-rounder.See the tubers
Sweet Potato - Eclipse TubersPurple flesh, white skin. Dense and drier, makes a violet mash.See the tubers
Sweet Potato - Northern Star TubersWhite flesh, red skin. Early, heavy cropping, great for chips.See the tubers
More sweet potato guides
Frequently asked questions
How many sweet potatoes do you get from one tuber?
One planting tuber usually produces several slips, often eight or more if it is kept producing for a few weeks. Each slip grows into a plant that can set several good sized tubers plus smaller ones, so a single tuber can fill a bed.
Can I plant the whole tuber in the ground like a potato?
You can, but it is wasteful and usually gives a poorer crop. Sweet potatoes are grown from slips cut from the tuber, so one tuber becomes many plants instead of one.
How long do sweet potatoes take to grow?
About four to five months from planting the slips, and closer to five in cooler districts. The vines are usually ready to lift when the leaves start to yellow, and always before the first frost.
Do sweet potatoes need full sun?
Yes. They will tolerate part shade but crop far better with at least six hours of direct sun. Warmth is what drives tuber formation.
Why did I get lots of leaves and hardly any tubers?
Too much nitrogen, too much shade, or too short a season are the usual causes. Vines that were allowed to root along their length can also spread their energy into many tiny tubers instead of a few good ones.
Can I eat the leaves?
Yes. The young shoot tips and leaves are a traditional green in many cuisines and cook like spinach. A light picking every week or two costs the crop very little; heavy picking reduces the tuber yield.
Can you ship sweet potato tubers to WA or Tasmania?
No. Due to quarantine restrictions and our shipping policy, we cannot send sweet potato tubers to Western Australia or Tasmania. If you are unsure whether your address is affected, please contact us before ordering.