How to Grow Sweet Corn from Seed

Sweet corn plants require isolation from other corn types, including other sweet types, popcorn, ornamental corn, and silage corn. To be on the safe side, isolate sweet corn types with a surrounding buffer zone 76 m (250′) wide. Another way to accomplish isolation is to sow different corn types at least two weeks apart.

Culture: Sweet corn will grow in most soil types, but it is best grown in a sunny, wind-sheltered site with a well drained, organic soil. Avoid sites where the soil suffers from extremes of wet or drought. Soil pH should be between 5.5 to 6.5.

You should plant treated seed after all danger of frost is past and the soil has warmed up to at least 13 C (55 F). Planting your seed any sooner delays germination, which, in turn, drastically increases the chance that the seed will be destroyed by insects or rot before sprouting.

Avoid Sowing in Cold Soil

Sweet corn seeds are very sensitive to cold or wet conditions during the first 24 hours after planting. Do not plant as a sharp cold front approaches or when heavy rain is expected in the next 24 hours. Planting in cool soil is the single biggest reason for a poor crop.

Minimum Soil Temperature for Sweet Corn Varieties

  • Normal Cultivars (su) — 13 C (55 F) minimum soil temperature
  • Sugar Enhanced (se) — 16 C (60 F) minimum soil temperature
  • Supersweets (SH2) & Triple Sweets — 18 C (64 F) minimum soil temperature

For untreated seed, please wait until the soil has warmed to at least 18 C (64 F).

When planting in rows, space the seed 10-15 cm (4-6″) apart, later thinning to 20-30 cm (8-12″) apart with the rows 55-75 cm (22-30″) apart. To ensure proper pollination, plant at least 3 to 4 rows.

Corn can also be planted with 3 to 4 seeds per hill, in hills spaced 30 cm (12″) apart. Plant 250 gr (1/2 lb) to a 30 m (100′) row or 4.5-6.8 kg (10-15 lbs) per acre. Work in a good general vegetable fertilizer at planting, keep weeds under control and the soil evenly watered throughout the season.

Sufficient water is particularly important at flowering time and when the cobs begin to fill. Cobs are generally ready for harvesting when the ‘silks’ turn dark brown. To check for optimum maturity, gently peel back a section of the husk and press your thumbnail into a kernel. If the liquid is a milky colour, the corn is ready. Should it be clear, the corn is immature and, if it is thick, the corn is over-mature and probably tough.

Sweet corn is untreated for home garden use. Delay sowing untreated seed until soils have warmed to 18 C (64 F), otherwise germination may be spotty or not at all. Commercial growers will be shipped treated seeds, unless they specifically order untreated seeds. Packages will be 250 g or less (untreated only).

Super Sweet Corns

Triple Sweet Corn — Cobs produce 75% (SE) sugary enhanced kernels and 25% (SH2) supersweet kernels for delicious, long lasting sweetness.

Synergistic Corn — Another sweet combination of 75% (SE) sugary enhanced kernels and 25% (SH2) supersweet kernels for a longer harvest window. Synergistic corn is less sensitive to cold soil conditions. They do not need isolation from SU and SE corns.

Augmented Corn — This sweet corn combines the best of both worlds with a sweetness and bite that is truly unique. These varieties have 100% of the kernels containing the SH2 supersweet characteristic, but also have SE and SU traits in a proportion of the kernels for extra taste/quality. These varieties need to be isolated.

Note: Effective November 1, 2016 we are offering Bodacious, Peaches and Cream, and Honey Select as treated seed. Big Jim II is offered as treated seed only.

View ‘How to Grow’ Guides for other vegetables here.

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