Yam Growing Guide
How to Grow Yams
Yams, or oca as they’re known in most other parts of the world, are an easy and rewarding crop to grow at home.
They produce heaps of small, colourful tubers with a slightly tangy flavour that becomes sweeter after harvest. They’re brilliant roasted and grow in much the same way as potatoes, although they do take a little longer to develop.
Yam Growing Guide at a Glance
| When to plant | September to November |
| When to harvest | May to July |
| Growing time | Around 6 to 8 months |
| Position | Full sun |
| Planting depth | 5 to 8cm |
| Spacing | 30 to 40cm apart |
| Soil | Rich, loose and free draining |
| Suitable for pots | Yes |
What Are Yams?
The yams we grow here are actually oca, with the botanical name Oxalis tuberosa.
They’re not the same as the large tropical yams grown overseas. Oca plants form low, leafy growth above the ground and clusters of small tubers beneath the soil.
The tubers can be yellow, orange, pink or red, depending on the variety.
When to Plant Yams
Plant yams in spring once the risk of hard frost has passed and the soil has started to warm.
In warmer areas, planting can usually begin from September or October. In colder areas, it may be better to wait until October or November.
Avoid planting into cold, soggy soil. Yams like moisture, but they don’t like sitting in water.
Should You Sprout Yams Before Planting?
You can plant yams without sprouting them first, but giving them a head start can be useful, especially in colder areas.
Place your seed yams in a shallow tray or cardboard box in a bright, dry and frost-free position.
Once short shoots begin to appear, they’re ready to plant. There’s no need to wait until the shoots become long, as shorter sprouts are much easier to handle.
Choosing the Best Position
Choose a spot that receives full sun for most of the day.
Yams grow best in:
- Full sun
- Loose, fertile soil
- Free-draining ground
- Soil that stays evenly moist
- A position protected from late spring frosts
If your soil is heavy clay or tends to stay wet, grow yams in a raised bed or large pot.
Preparing the Soil
Loosen the soil to around 20 to 25cm deep and mix through plenty of compost or well-rotted organic matter.
Yams like rich soil, but don’t go too hard with high-nitrogen fertiliser. Too much nitrogen can give you heaps of leafy growth without improving the crop underneath.
If your soil is poor, a balanced vegetable fertiliser can be added before planting.
How to Plant Yams
- Dig a shallow trench or individual planting holes around 5 to 8cm deep.
- Place the seed yams into the soil with any shoots facing upwards.
- Space them around 30 to 40cm apart.
- Leave roughly 50cm between rows.
- Cover with soil and water well.
The shoots can take a few weeks to appear, especially if the soil is still cool.
Mounding Yam Plants
As the plants grow, gently draw loose soil or compost around the base of the stems.
This helps support the plants and gives the developing tubers plenty of loose soil to grow into.
You don’t need to mound them as heavily as potatoes. Just build the soil up gradually as the plants grow.
Watering Yams
Yams need regular water throughout spring, summer and early autumn.
They hate drying out, so water deeply during dry spells and add a good layer of mulch around the plants.
Mulch helps hold moisture in the soil, keeps weeds down and stops the ground from heating up too much.
Keep the mulch slightly away from the main stems to reduce the chance of rot.
Feeding Yam Plants
If you’ve prepared the soil with compost, they usually won’t need much extra feeding.
In poor soil, apply a balanced vegetable fertiliser during the early part of the growing season.
Avoid repeated applications of high-nitrogen fertiliser, as this can encourage the plants to put all their effort into leaves rather than tubers.
Growing Yams in Pots
Yams grow very well in pots, planter bags and large tubs.
Choose a container at least 40cm wide and 30cm deep, with plenty of drainage holes.
Fill it with a good-quality vegetable mix and compost, then plant one to three seed yams depending on the size of the container.
Keep the pot in full sun and water regularly. Pots dry out much faster than garden beds, so keep an eye on them during hot weather.
One of the best things about growing yams in pots is that harvest is easy. Simply tip the container out onto a tarp and have a good rummage through the soil.
When Do Yams Form Tubers?
Yams spend most of spring and summer growing plenty of leafy tops.
The tubers begin forming and swelling later in the season as the days become shorter.
This is why it pays not to rush them. Even if the plants look huge in early autumn, the crop underneath may still be quite small.
Keep watering during early autumn if the weather is dry, as this is an important time for the tubers.
When to Harvest Yams
Yams are usually ready to harvest from late autumn into early winter.
Wait until the foliage has yellowed, collapsed or been knocked back by cold weather.
The tubers do much of their growing late in the season, so digging too early can make a huge difference to the size of your crop.
If your soil drains well, you can leave them in the ground for another week or two after the tops die back.
Don’t rush them. Yams reward patience.
How to Harvest Yams
Use a garden fork to loosen the soil around the outside of the plant.
Start farther away from the centre than you think you need to, as the tubers can spread beyond the main crown.
Lift the soil gently and search through it by hand.
They can be easy to miss, so it’s always worth going back through the soil a second time.
Avoid digging too aggressively with a spade, as the tubers are easily sliced or bruised.
How to Make Yams Taste Sweeter
Freshly harvested yams can have a sharp or tangy flavour.
Leaving them in a bright, dry position for several days can help make them sweeter.
Spread them out in a single layer somewhere protected from rain, birds and rodents.
Try cooking a few after several days. If you still find them too tangy, leave the rest a little longer.
How to Store Yams
Allow freshly harvested yams to dry before storing them.
Don’t wash them until you’re ready to use them, as damp tubers are more likely to rot.
Store them in a cool, dark and well-ventilated place. Check them occasionally and remove any that become soft or show signs of decay.
Keep a few of your healthiest tubers aside for planting again next spring.
Common Yam Growing Problems
Lots of Leaves but Not Many Yams
The most common reason is harvesting too early.
Yams develop most of their tubers late in the season, once the days begin getting shorter.
Too much nitrogen can also produce heaps of leafy growth without much happening underneath.
Small Yams
Small tubers can be caused by dry soil, overcrowding, poor soil or digging the crop too early.
Give the plants plenty of room, keep them watered and leave them in the ground until the foliage has properly died back.
Plants Wilting in Summer
Check the soil moisture. Yams dislike drying out and can wilt quickly during hot weather.
Water deeply and add more mulch if needed.
Tubers Rotting in the Ground
This is usually caused by poor drainage or waterlogged soil.
Raised beds, pots or improved soil are the best options if your garden stays wet.
Frost-Damaged Leaves
Young yam plants are frost tender.
Use frost cloth if a late frost is expected during spring.
Frost damage later in the season is less of a worry, as it usually means harvest time is getting close.
Slug and Snail Damage
Slugs and snails can chew the young shoots and leaves.
Check around the plants at night and use your preferred slug-control method if needed.
Frequently Asked Questions
Are Yams the Same as Kūmara?
No. Yams are oca, while kūmara are sweet potatoes. They’re completely different plants.
Can I Plant Yams Bought from the Supermarket?
They may grow, but their health, variety and storage history are unknown.
Seed yams supplied for planting are generally a more reliable option.
Can I Cut Yams Before Planting?
It’s best to plant them whole.
Cutting them increases the chance of rot and usually isn’t necessary.
Do Yams Need Full Sun?
Full sun is best.
Plants grown in too much shade may still produce lots of leafy growth, but the crop underneath is likely to be smaller.
Do Yams Need to Be Mounded Like Potatoes?
A little mounding is useful, but they don’t need huge ridges.
Just gradually draw loose soil or compost around the stems as they grow.
Why Are My Yams Sour?
Freshly dug yams naturally have a tangy flavour.
Leaving them in a bright, dry position for several days can help sweeten them.
Our Final Yam Growing Tip
The biggest mistake gardeners make with yams is digging them too early.
The plants may look ready at the beginning of autumn, but most of the crop develops once the days become shorter.
Keep them watered, wait for the tops to die back, then enjoy the treasure hunt.
