How to grow Sweet Corn in New Zealand
Home-grown sweet corn picked minutes before cooking is far sweeter than anything in the shops, because the sugars start turning to starch as soon as a cob is picked. Corn is a hungry, frost-tender summer crop that needs warm soil and full sun. It is wind pollinated, so it must be planted in a block rather than a single row.
📖 Our full guide: How to Grow Sweet Corn in New Zealand
At a glance
When to sow by region
| Region | When to sow | Regional note |
|---|---|---|
| Northland | October and November | |
| Auckland | October and November | |
| Waikato & Bay of Plenty | October and November | |
| Central North Island | November and December | |
| Wellington & Lower North Island | November and December | |
| Nelson & Marlborough | November and December | |
| Canterbury | November and December | |
| Otago & Southland | December | |
| Central Otago | December |
Not to be confused with: Popcorn and maize, which are grown the same way but should be kept well apart from sweet corn, as cross-pollination spoils its sweetness.
Where to plant
Grow sweet corn in full sun, sheltered from strong winds, in rich, fertile, well-drained soil with plenty of compost or manure dug in. Plant a block of short rows, at least four rows of four plants, rather than one long row, so pollen falls from the tassels onto the silks of neighbouring plants. Grow only one sweet corn variety at a time, and keep popcorn and maize well away, as they cross-pollinate easily.
- Northland, Auckland, Waikato and Bay of Plenty: sow directly from October, once the soil is warm and frosts are over, and keep sowing in succession into summer.
- Central North Island, Wellington, Nelson and Marlborough, and Canterbury: sow in November and December.
- Otago and Southland and Central Otago: sow in December, or start seed in pots under cover and plant out once frosts are over. Choose an early variety.
Choosing a variety
- Golden Sweet: sweet, juicy golden corn with well-filled cobs, good early vigour and good resistance to common rust.
- Bicolour: a supersweet yellow and white corn with 18 to 20 cm cobs, good tip fill and good resistance to common rust.
- Honey Sweet and True Gold: a reliable supersweet hybrid and an open-pollinated golden corn with old-fashioned flavour.
- Early varieties such as Kelvedon Glory are the best choice for cool springs and short seasons.
How to plant
- Dig compost or well-rotted manure into the bed before sowing.
- Check the forecast: a cold, wet spell just after sowing reduces germination.
- Sow two seeds per hole, 2.5 cm deep, with holes 20 to 40 cm apart, in a block of at least four short rows.
- Water in well, then wait until seedlings appear before watering again.
- When seedlings are about 15 cm tall, thin to the stronger plant in each hole, then mulch with pea or lucerne straw.
Watering and feeding
Water regularly and deeply, especially from tasselling until the cobs fill, as dry soil at that stage gives poorly filled cobs. Mulch to hold moisture.
Corn is a hungry crop. Side-dress with compost or a nitrogen-rich fertiliser as the plants grow.
Pruning and care through the year
- When the tassels are shedding pollen, give the plants a gentle shake on a dry morning to help pollen fall onto the silks. Each kernel only forms if its silk is pollinated.
- There is no need to remove side shoots.
- Net or bag the cobs if birds are a problem.
Harvesting
Corn is ready when the silks have turned brown and dry and a kernel squeezed with a thumbnail gives milky juice, not watery or doughy. Twist the cob down and off the stalk.
Pick just before cooking, as the sugars start turning to starch straight away. Keep cobs in their husks in the fridge and use within two days, or blanch and freeze the kernels.
Growing in pots
Corn is not ideal in pots, as it needs a block for pollination. If you try, use several large pots at least 30 cm wide and deep, grouped together in full sun out of the wind, with two seeds per pot.
Using it
Boil, steam, barbecue or roast cobs, or cut the kernels off for fritters, salads, salsas, soups and chowders.
Companion planting
Sweet corn is part of the traditional 'three sisters' planting with beans and squash.
Good companions
- Beans Beans add nitrogen to the soil, and climbing beans can use the stalks as supports.
- Pumpkin Its large leaves shade the soil, holding moisture and smothering weeds under the corn.
- Zucchini Another squash that covers the ground between corn rows.
- Cucumber Likes the same warm, rich, well-watered conditions.
Keep apart
Avoid planting these close to sweet corn.
- Tomato Tomatoes and corn share the corn earworm caterpillar, which attacks both.
Pests and diseases
Caterpillars in the cobs and birds are the main problems in New Zealand gardens.
Pests to watch for
- Caterpillars Corn earworm caterpillars in the tip of the cob, eating the kernels, with droppings and rot.
- Birds Seed dug up after sowing, and husks torn open to eat ripening kernels.
- Aphids Colonies on tassels and leaves, with sticky honeydew.
- Slugs Seedlings chewed off, with slime trails.
Diseases to watch for
- Rust Small, raised, rusty-brown pustules on leaves. Choose rust-resistant varieties.
- Smut Large, grey, swollen galls on cobs or tassels that burst to release black spores. Remove and bin galls before they burst.
- Northern corn leaf blight Long, cigar-shaped grey-green to tan lesions on the leaves in humid weather.
Common questions
Why are my corn cobs only half filled?
Poor pollination. Plant in a block rather than a single row, keep the soil moist at tasselling, and shake the plants gently when the tassels are shedding pollen.
When do I plant sweet corn in New Zealand?
Once the soil is warm and frosts are over: from October in the warm north, November in Wellington, Nelson, Canterbury and the central North Island, and December in Otago, Southland and Central Otago.
How do I know when corn is ready?
The silks turn brown and dry, and a kernel squeezed with your thumbnail gives a milky juice.
Can I grow sweet corn and popcorn together?
Keep them well apart or grow them in different seasons. They cross-pollinate easily, which makes sweet corn starchy.
How many cobs does a corn plant produce?
Usually one large cob per plant, sometimes with a smaller second cob. Grow enough plants for your household.
Why did my corn seed not come up?
Cold, wet soil after sowing is the usual cause. Wait for warm soil, check the forecast, and sow two seeds per hole.
Sources we checked: Yates NZ: How to grow sweetcorn; Yates NZ: Common problems of corn; Kings Seeds: Corn Golden Sweet F1; Kings Seeds: Corn Bicolour F1.