Most vegetables start from a seed packet. Sweet potatoes start from a tuber on the kitchen bench, and the method is simple once it has been explained.
The tuber you receive is planting stock, not the crop. Its job is to grow shoots, and those shoots, called slips, are what go in the garden. A single tuber can fill a bed. Kept cold and wet, it rots, so the details matter.
When should you start?
Start sprouting four to six weeks before you plan to plant, which for most of Australia means August or September. Slips go into the garden after the last frost, once the soil is warm, so count back from your planting date.
In the subtropics, a tuber started in early August is ready for a September planting. In temperate gardens, start in late August or September for October or November planting. Cool districts can start in September for a November planting, and a warm spot indoors matters more there than anywhere. Our zone by zone sweet potato calendar has the planting dates for each region.
The tray method
Lay the tuber on its side in a shallow tray or pot, and cover the lower half with moist seed-raising mix or potting mix. Keep the mix damp but never soggy, and put the tray somewhere warm and bright, such as a sunny windowsill, a heated propagating mat or a warm verandah out of the wind.
Shoots push up along the top of the tuber within two to four weeks. Because the base of each shoot sits in mix, it starts forming its own roots while it grows, which is why this method gives sturdier slips than the jar. A tuber in a tray can keep producing new shoots for six weeks or more if you keep it warm.
The jar method
Push three or four toothpicks around the middle of the tuber and sit it on the rim of a jar so the lower third is in water. Stand it in a warm, bright spot. Change the water every few days so it stays fresh.
Roots grow into the water first, then shoots appear from the top. It is slower than the tray and the shoots are a little softer, but it is a good way to watch the process, and children enjoy it. If the bottom of the tuber turns soft or the water smells, the tuber is too wet or the spot is too cold. Start again with a fresh tuber, fresh water and a warmer position.
Which end goes down?
The root end goes down and the stem end goes up. The stem end is the one that was attached to the plant, and it is the end that sprouts, so it needs to sit above the water or the mix. On a washed tuber the two ends can be hard to tell apart, so if in doubt lay the tuber on its side in a tray and it will send roots down and shoots up on its own.
How warm does it need to be?
Ordinary indoor temperatures in spring are enough. Sweet potatoes shoot readily at room temperature, grow slowly below about 15°C, and can rot if kept cold and wet. A windowsill above a warm kitchen, the top of the fridge or a heated propagating mat all work. A cold garage or a south-facing sill in September usually does not.
How do you cut and root the slips?
Once a shoot is 15 to 20 cm long with several leaves, hold it near the base and snap or snip it off the tuber. Strip the lowest two or three leaves, then stand the slips in a glass of water on the windowsill. White roots usually appear within a week.
Slips from the tray method may already have roots, and those can go straight into a small pot of potting mix to grow on. Either way, a slip with a good root system settles into the garden faster than a freshly cut one, which matters most in short-season districts.
How many slips will you get?
Expect eight to ten slips from a healthy tuber over a few weeks, and more from a large tuber that is kept warm and producing. Two tubers are usually enough for a family bed, and a pack of four comfortably plants a larger patch or lets you try a variety in more than one spot.
Do not take every shoot at once. Cut the biggest, leave the smaller ones to grow on, and come back in a week. The tuber keeps producing as long as it is warm, moist and has not been allowed to shrivel.
Hardening off and planting out
Give rooted slips a few days outside in a sheltered, shaded spot before they go into the garden, so the leaves toughen up. Then plant them 30 to 40 cm apart in a sunny, well drained bed, laid at a slant with two thirds of the stem buried, and water daily for the first week.
Slips often wilt for a day or two after planting and then recover. Plant in the late afternoon and keep the water up. The full guide to growing sweet potatoes takes it from here.
What if nothing happens?
Give it time and warmth. A tuber that has not shot after four weeks is almost always too cold, so move it somewhere warmer. If the tuber is firm and the spot is warm, it may simply be resting.
- Soft, smelly tuber: too cold and too wet. Discard it and start a fresh one somewhere warmer.
- Tall, pale, floppy shoots: not enough light. Move the tray to a brighter spot.
- Shoots but no roots on the cut slips: change the water more often and keep it warm.
- Purple or bronze skin, or variable colour inside: normal for the variety and season, and no problem for sprouting. Our variety comparison shows what each one should look like.
Our foundation seed tubers are supplied clean, with no post-harvest treatments, so they shoot readily. Supermarket sweet potatoes are cured and held in cool storage to keep sprouting down, so they can be slow and unreliable to shoot. If you have tried the jar method before and had nothing happen, that may be why. You can find the tubers in our sweet potato tuber collection, and the full growing guide covers the rest of the season. For more ways to start plants without seed, see our other propagation guides.
Due to quarantine restrictions and our shipping policy, we cannot send sweet potato tubers to Western Australia or Tasmania.
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 long does it take to grow sweet potato slips?
Usually two to four weeks for the first shoots, and four to six weeks to have well rooted slips ready to plant. Warmth is the main thing that speeds it up.
Can I plant the tuber straight into the garden instead?
You can, but you will get one plant from a tuber that could have given you eight or ten. Sprouting slips is the reason to buy planting tubers.
Do I need to cut the tuber in half?
No. A whole tuber sprouts perfectly well and is less likely to rot. Cutting it is only useful if you want to sprout a very large tuber in two small trays.
Can I take cuttings from the vines later in the season?
Yes. Once the vines are growing, 20 to 30 cm tip cuttings root easily in water or moist soil and can be planted the same way as slips. It is a good way to fill gaps or start a second bed.
What do I do with the tuber once it has finished producing?
Compost it. It will be soft and spent by then. Keep a few of the best tubers from your own harvest next autumn if you want to sprout slips again the following spring.
Can you ship 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.