GardenLine | Vegetables | Growing Sweet Corn

- do not plant corn into a cold (less than 17C) wet soil. These conditions favour the growth of fungi which can rapidly rot the seed. Ensure the seed is fungicide-treated if planting into cool soils.

- soaking seeds in water for about 4 hours may speed up germination. If you soak your seeds, you must plant them in warm moist soil; dry soil will inhibit germination. More simply, plant dry seeds and water thoroughly.

- plant corn in a square or block pattern rather than in long, thin rows. Corn is wind-pollinated, and square planting patterns result in greater pollination. A minimum of 100 plants in a block is suggested for optimum pollination. Missing kernels in a corn cob are an indication of poor pollination.

- do not remove the tassels at the top of the plant; the tassels constitute the male portion of the plant which supplies the pollen. The fine, yellow dust (pollen) shed by the tassels falls onto the silk of the cob, which is the female portion of the plant. Each silk thread is attached to a kernel. If no pollen falls onto the silk, no kernel will form. Shaking the plants when the pollen is being shed can help increase pollination.

- choose varieties that will mature within our approximately 100-day growing season. Most seed companies are located in eastern Canada, where growing conditions are more favourable than ours. A variety listed in a catalogue as maturing in 55 days will usually require 85 days in Saskatchewan. It is wise to add 30 days to the listed maturity date to determine the maturity date in Saskatchewan. This rule of thumb will change from year to year, but overall proves to be fairly reliable.

- since corn is wind-pollinated, cross-pollination can occur if different types or colours (yellow, white or bi-coloured) are planted close to each other. In order to ensure maximum quality, keep each type (normal sweet corn, sugar-enhanced and super-sweet) well isolated from each other - preferably by at least 30.5 m (100 feet) apart. It is also essential to keep popping corn, ornamental corn, and field corn well isolated from sweet corn varieties. If cross-pollination does occur, sugar levels, colour, popping quality and other characteristics will not be as anticipated. To avoid isolation, different types of corn can be planted close together as long as their maturity dates have a difference of at least 7 days. This way, when one variety is shedding pollen, the other variety will not be receptive to pollen.

- as soon as the cobs are harvested, the sugars in the kernels quickly convert to starches. This produces a less sweet product. To ensure maximum sweetness, cobs should be immersed in ice cold water as soon as possible after picking, and left in the water until eaten. Shade from hot sun as much as possible. Many homeowners take pails of water and ice out to the garden when harvesting corn. Try it - it's well worth the effort!

Due to consumer demand, plant breeders over the past decade have significantly improved the quality of sweet corn. Numerous types of sweet corn are now available to homeowners, and it is important to know about these types in order to obtain maximum quality.

Normal Sweet Corn or Sugary Normal: Abbreviated Su, Su+, Su++. These have been, and still are, very popular with home gardeners, partly because they will germinate in cool soil (10C). Varieties have varying degrees of sweetness, but unfortunately the sugars convert to starches after harvest quite quickly. A new group of normal sweet corn called 'All Sweets' is much sweeter than the average for this type.

Sugar Enhanced: Abbreviated SE or EH. This type is most prized for its very tender kernels that are easy to chew. The sugar content is greater than normal sweet corn, reportedly much the same as 'All Sweets'. After harvest, sugars are not converted to starches as fast as normal sweet corn varieties. Sugar-enhanced varieties should not be planted as early as normal sweet corn varieties, for they need a warm (17C) soil temperature for germination.

Supersweet or Shrunken: Abbreviated Sh2. This type of sweet corn produces kernels that are at least twice as sweet as normal sweet corn, and also sweeter than sugar-enhanced varieties. The sugars do not convert to starches nearly as fast after harvest. Unfortunately these varieties need a warm (17C) soil temperature for good germination. Isolation from other corn types is essential!

The Department of Horticulture Science has tested numerous varieties of corn over the past few years. Although these tests are aimed more at commercial producers, many market gardeners and homeowners with large corn patches can benefit from the results. If you wish to have a copy of the results, please write to the Department of Horticulture Science, University of Saskatchewan, Saskatoon, Sask., S7N OWO, attention: Garden Line.

Some of the varieties that have performed well in this area, and that are recommended for homeowners include: Buttervee (Su++), Classic Touch (Su+), Maple Sweet (SE), Northlite (Su), Polarvee (Su), Spartan (Su++), and Sweetie (Sh2). This list is by no means complete, as many other varieties are likely suitable, but have not yet been tested by the Department.

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Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.