How to grow sweetcorn
Overview
Sweetcorn (Zea mays var. saccharata) is a warm-season grass grown for its sweet kernels. It is wind-pollinated, so planting in blocks rather than single rows ensures good ear fill. Consistent moisture and warm soil are critical for a successful crop.
Varieties
- Peaches and Cream — Bicolour sweetcorn with excellent flavour, widely grown in Australian home gardens.
- Honey and Cream — A popular bicolour variety in New Zealand, known for high sugar content.
- Goldstar — Yellow sweetcorn with good disease resistance, suited to warmer zones.
- Sweet F1 — Hybrid supersweet variety that holds sweetness longer after picking.
- Jolly Roger — Early-maturing yellow sweetcorn, reliable in temperate and subtropical climates.
Soil Preparation
Sweetcorn thrives in loamy, well-drained soil with pH 6.0–6.8. Incorporate 5–10 cm of well-rotted compost or manure before planting. Avoid heavy clay that impedes root development.
Growing Guide
Sow seeds directly in blocks of at least 4 rows, spacing 20-30 cm apart with 75 cm between rows. Plant 2-3 cm deep in rich, well-drained soil; germination takes 7-14 days at soil temperatures above 15°C. Water regularly, especially during tasselling and silking, applying 2-3 cm per week. Side-dress with nitrogen when knee-high and again as tassels appear to support rapid growth.
Sowing
Direct sow 2-3 cm deep after all frost risk has passed and soil is warm (above 15°C). Seeds can be started in punnets in cold districts, but transplant carefully to avoid root disturbance. Thin seedlings to 20-30 cm apart once they reach 10 cm tall.
Care
Apply a balanced fertiliser at planting and side-dress with a nitrogen source (e.g., blood and bone) when knee-high and again at tasselling. Mulch thickly to retain moisture and suppress weeds. Remove side suckers only if they crowd the block.
Companion Planting
Good companions include climbing beans (which fix nitrogen), squash or pumpkin (which shade the soil and suppress weeds). Avoid planting near tomatoes or potatoes to reduce shared pest pressure like corn earworm.
Common Pests & Risks
Corn earworm (Helicoverpa armigera) is the main pest – apply mineral oil to silks three days after pollination or use Bt sprays. Watch for cutworms on young seedlings and aphids on leaves. Encourage beneficial insects like ladybirds and parasitic wasps.
Harvesting
Harvest when silks turn brown and kernels emit a milky juice when pierced. Pick early in the morning and eat immediately for best sweetness, or blanch and freeze. Each ear is ready about 20 days after silking.
In the Kitchen
Sweetcorn is best eaten within hours of harvest as sugars convert to starch quickly. Boil, steam, grill, or roast whole ears; kernels can be cut off for salads, salsas, or freezing. For maximum sweetness, blanch ears in boiling water for 3-5 minutes before freezing.
Troubleshooting
Gappy ears: Poor pollination – plant in blocks of at least 4 rows. Stunted yellow plants: Nitrogen deficiency – side-dress with a high-N fertiliser. Worms in ears: Corn earworm – apply mineral oil to silks after pollination. Leaf rust: Fungal disease in humid conditions – ensure good airflow and avoid overhead watering. Tassels drying prematurely: Heat or water stress – maintain consistent soil moisture during flowering.