Sweet potatoes are easy to grow in the Bega Valley. They are a great staple as not only are they a root crop, but all parts of the plant are edible. Sweet potato greens are a delicious spinach substitute.

How to plant sweet potato

Sweet potatoes need warm soil. They should not be planted out if overnight temperatures are under 10ºC. Ideally the soil temperature will be above 18ºC.

Choose a location with space for the plants to run. Sweet potatoes create a dense, spreading ground cover. They can be planted as close as 30cm together in a row if there is good fertility and moisture available. Plant up to 80cm apart in the row to reduce competition if the conditions are tougher. Allow around 1m between rows. They prefer full sun but will also grow very successfully in locations with morning or afternoon shade. A minimum of 6 hours of direct sun is sufficient.

Put your plant as far into the ground as you can without burying the leaves. Roots will form along any buried stem to help feed the plant.

Can I grow in a pot?

Yes but the production of roots will be limited by the pot size. If you are mainly growing to eat the greens this isn’t a consideration. If you want to produce good sized roots then select a pot or bag that is a minimum of 40cm diameter and preferably bigger.

Tips for growing successfully

Sweet potatoes prefer warmth and adequate moisture and only moderate fertility to produce good roots.

High fertility will produce more leaf growth at the expense of roots. Avoid manures and nitrogen rich fertilisers. Most gardeners growing in soil will not need to add any fertiliser unless their soil is of very low fertility. Growers using pots may need to apply fertiliser. If fertiliser is required it is best applied about 4 weeks after planting.

Loose friable soil will best support root production. If growing in heavy soil it is best to create raised beds. A sandy soil is their preference but using lots of compost and mulch to form ridges for planting will avoid the issues of compacted soils. You can use woodchips plentifully as a mulch if they are available.

You can trim the vines to keep it more compact if it starts to overtake paths or adjoining plants, but pruning is not necessary for good root production.

Be aware that spreading vines may put down roots wherever they touch soil and produce roots in those locations. To avoid getting many tiny roots it can be useful to lift the vines occasionally to discourage rooting along their length and encourage the formation of larger roots at the original planting site.

When to harvest

You can harvest the green shoots at any stage. Be aware that taking lots of leaf early in the season may impact root production. But the plants usually produce plentifully so harvesting a bunch of leafy shoots every week is unlikely to impact root production noticeably.

Roots are ready to harvest as soon as they are a suitable size. The speed at which they are ready will be dependant on your local conditions. Start checking after 3 to 4 months from planting but they may not be ready until 5 or 6 months. You may be able to see them pushing up the soil at the original planting location. Scrape away any mulch to see if there are any tubers visible at the surface. Alternatively you can leave them to continue growing until the colder weather starts to turn leaves yellow or brown.

Be careful using a fork to dig them up as it is very easy to damage the roots. Pulling on the main crown of the plant may enable you to use your hands to dig out the roots.

The tubers need careful handling as they bruise fairly easily and damaged skin can encourage rotting during storage.

Do not wash the tubers. Keep them dry and gently brush off soil.

In our local climate the tubers can also be left in the ground until the plants have completely died back as our frosts are not heavy enough to damaged buried tubers. However wet, cold soil can encourage the tubers to rot so it’s best to harvest them before heavy rain if they are not actively growing.

How to store

Keep the tubers in a warm location for the first few weeks. Above 25ºC is ideal. This helps the skin to cure and can improve flavour. Cure in a single layer in a cardboard box indoors or a warm shady outdoor location. Keep the box closed or cover with a cloth so they don’t dry out too quickly.

Check through all the sweet potatoes and use any damaged ones quickly. Only store tubers without blemishes.

After curing move them to a cool (10 to 15ºC) location and continue to keep them covered. Well kept sweet potatoes should store for 6 months (if you don’t eat them faster!).

There are several ways to propagate more sweet potato plants – cuttings and slips

Sweet potatoes grow easily from cuttings. You can take tip cuttings at the end of the season before cold damages or stops growth and pot them up. In the Bega Valley around April is usually a good time to do this.

Aim to make your tip cuttings about 10cm long. Cut just below a node. Remove all the leaves up the stem leaving only the very immature leaves at the tip. The goal is to remove enough leaves so that transpiration is reduced since they do not yet have roots to help replace lost moisture.

Multiple cuttings can be put into a pot together. Keep the pot in a warm, sheltered place over winter. In very cold areas they are best kept as an indoor plant until spring.

When planting out pots that had multiple cuttings grown in them, use a sharp knife to cut the multiple plants apart before planting them out described in the Growing section.

Slips are the sprouts that form from the tubers. Store a few tubers over winter ready for spring slip production. Chose a warm sheltered space for your slip production. You may want to put some cardboard down first to stop weeds from invading your production space. Lay your roots down. They can be quite close together. Cover them with compost, soil or potting mix. Keep them well watered until the shoots appear. This stage may take weeks, so be patient, keep them warm (above 10ºC and preferable above 18ºC) and don’t let them dry out. When the shoots are large enough to handle you can gently pull them away from the root for planting out. They should each have their own roots.

These rooted shoots are called slips because they can be ‘slipped’ off from the parent root. Leave the root in place. It will produce many slips. It will take about 2 months to produce slips from your tubers. Which is why home growers often keep a few cuttings from the previous season as they are ready to go as soon as the soil it warm enough.

If slips don’t have their own roots (or only a few as shown in the video clip above) they should be treated in the same way as cuttings and potted up until they produce roots. A well rooted slip can be planted directly out into the garden as long as the soil is warm enough. Be careful not to allow the small, new roots to dry out. Putting them into a bucket of water and taking the bucket to the garden when planting them out is one way to avoid this issue. Excessive leaves may still need to be trimmed from slips to reduce transplant shock.