How to Plant, Grow, and Harvest Sweet Corn at Home

Botanical Name: Zea mays

Plant Type: Tender Annual

There is only one way to experience the true taste of sweetcorn, and that is to grow it yourself. Corn originated in Central America and the Native Americans relied on it to produce flour, porridge (called hominy grits by settlers), and popping corn. They also maintained strains for ‘green’ corn that was sweet and harvested ‘in the milk’, that is when a corn kernel would ooze a milky substance when pierced.

The cobs were then slow roasted and dried to be mixed with beans to make the nourishing winter dish ‘succotash’. Today most gardeners want to grow ‘sweet corn’ with traditional corn flavour. These have been developed from the original Native American selections, however most varieties offered today are hybrids or ‘super sweets’. Their sugar levels are higher than the heirloom varieties, and the harvest time not as critical. Hybrids may have larger cob sizes and improved disease resistance, but they require higher soil temperatures to germinate than heirloom varieties.

As corn is wind pollinated, sow in blocks of a minimum of 16 plants to improve pollination. If growing more than one variety, avoid cross pollination by interplanting with taller plants such as sunflowers.

Varieties

Corn varieties fall into a number of groupings based on the end use of the cobs and kernels. These include the sweet corn, popcorn, which has small ears and hard kernels for popping in the oven, and flour corn (maize), which has full-sized cobs and large starchy kernels. In addition, some varieties have been developed for producing miniature baby corn, but most gardeners utilize the other types to meet their needs for baby corn by harvesting immature cobs when 7 cm to 10 cm long.

In Australia, the number of varieties of corn that are available is severely restricted due to the loss of many old varieties and quarantine restrictions preventing their replacement. Gardeners are therefore very limited in the types that they can grow, and it is only through good fortune that a number of heirloom varieties have been in the hands of enthusiasts and saved for the future.

Individual varieties vary in the quantity and colour of their kernels, the time they take for maturity and the number of mature cobs they produce. Heirlooms have a traditional corn flavour which is less pronounced in the new super sweet hybrids.

Cultivation

All corn types do best in sunny, open positions and it is particularly important not to establish plants in protected areas because wind movement is required for pollination. At the other extreme, don’t establish plants in locations subject to gales, because corn is a tall plant that can be damaged by strong winds.

Sun: Full Sun           

Pollination: Wind Pollinated

Soil: Corn needs well-drained soil and, while tolerating some acidity, does best in neutral soil. Its demand for nutrients is high and so plenty of manure needs to be worked into beds.

Growing from Seed

Sow: sow directly into prepared garden beds. Ensure that the ground is enriched with compost and weed-free. Sow in blocks.

Ease of Germination: Easy

Germination Temperature: 15-35°C

Germination Time: 21-25 days

Spacing: 20 cm apart in 1.2 m blocks

Harvest: 88–110 days

Yield: 1–3 cobs per plant approximately 120 g.

All corn varieties are warm-weather crops. In temperate regions corn is established in spring for summer to autumn harvest. It is very frost sensitive, so sowing should not take place until the risk of frosts has been well passed. Kernels need a soil temperature of at least 10°C for germination and require two weeks at 15°C and a week at 20°C for emergence. Kernels should be sown to a depth of 2-3cm and a spacing of 15-20cm and sow two seeds into the one hole/ 

It is important to sow the kernels as a block rather than a straight row, to facilitate pollination no matter which direction the breeze is blowing, and so that the plants provide some support for each other against the wind.

Add a thick mulch of organic matter around the base of the plants to help conserve moisture, insulate the roots and suppress weed growth. Sweetcorn is sturdy and shouldn’t need supporting.

Maintenance and Additional Care

Weed control can be a real problem in some areas. Diggers recommends mulching with newspaper topped with sugarcane mulch to prevent weed growth between your corn plants.  You can also try growing bush beans or peas as a cover crop underneath corn, to aid in weed control and to provide additional nitrogen for the plants.

Once established, it is essential to supply regular water as corn is shallow-rooted and any moisture loss will seriously affect the quantity and quality of the ears. Additions of liquid fertilizers to established plants is most beneficial and tends to promote additional cob development.

Companion Planting

Good companions: Amaranth, Beans, Broad Beans, Cucumber, Marigold, Marjoram, Peas, Potato, Pumpkin, Radish, Rockmelon, Squash, Sunflower, Watermelon, Zucchini.

Bad companions: Tomato.

Pests and Diseases

The main problem with growing corn is usually poor kernel development due to lack of pollination and poor ear development due to moisture stress. Snails and slugs can severely damage seedlings and should be controlled with baits or beer traps. Caterpillars often get into the top of the ear.

At times, aphids can also be a problem, and these too can be controlled with pyrethrum type sprays. Corn can also suffer from a number of soil-borne diseases encountered in other vegetable crops, and beds should be rotated each season to avoid their build-up. Animals and birds may be a problem at both seeding and harvesting time

Growing in Containers

A tall, narrow crop, corn grows well in containers and pots, however, for an effective harvest, you will need to plant several pots and block them together for easy pollination. Choose large pots at least 30cm wide and place 4-5 corn seed in the pot, spaced evenly to allow them room to grow. Use a premium potting mix specifically designed for vegetables. Organic mixes are always best for vegetable crops. Place in full sun and water regularly, especially during germination and corn development.

Harvesting

Depending on variety and climate, mature cobs can be harvested from 90 to 150 days after sowing. Some gardeners have difficulty determining when the ears of sweet corn are ready for harvest, and a good indication is the appearance of the silks at the top of the ear turning brown and drying out.

A simple test for maturity is to carefully pull back the leaves from the ear to reveal 30 per cent of the cob and forcing a fingernail against a few kernels. When under-ripe, a watery fluid will ooze out of kernels, when ripe the fluid will be milky, and when overripe it will look and feel lumpy.

If you are a little late in harvesting, kernels can still be salvaged for use in soups and relishes. Harvesting of popcorn and flour corn ears takes place when the leaves on an ear have turned brown and dry. Harvest the ears with the leaves still attached, peel them back, and store ears in a dry place for a few weeks before shredding the kernels from the cob.

Baby corn can be harvested from sweet corn varieties at any time, but most gardeners harvest mature ears early in the season and harvest baby ears late in the season, when there is no chance of them maturing.

Seed Saving

Seed Longevity: 2-3 years (non-sweet corn can last up to 5 years).

Isolation Distance: 800m

How to Save Seed: To save corn seed, leave the cobs to dry on the plant. When completely dry, they can be removed from the stalk. Peel back the leaves to expose the kernels. Hang to dry for a further 3-4 weeks in a warm dry location. When completely dry, the kernels should separate easily from the cob. These can then be store in a dry location for sowing next year.

Tips and Tricks for Success

• corn appreciates watering in very dry weather, particularly from late summer as the silks appear and the cobs begin to form.
• in southern Victoria and Tasmania, sowing should take place during November to December, and in northern Victoria and central New South Wales, sowing should take place during September to January. As one moves progressively north, the window for sowing widens, and in the tropics, corn can be grown throughout the year.
• at flowering, super sweet varieties must have a minimum 19°C soil temperature for germination and isolation from other corns to retain cob purity and flavour.