Sweet corn - perhaps the star of the summer garden.

June 15, 1998

This seems like a good time to talk about corn. It's mid-June, my early transplants are about 10 inches tall now, and the late corn, sown last, is up and growing.

There are quite a number of types of corn, including dent, flint, flour, and popcorn. When you say corn, though, most of us think sweet corn - Zea mays var. rugosa.

In an average year here in the Maritime Pacific Northwest, corn is sown about Memorial Day (the last weekend in May). However, as we all know the weather patterns of spring can be highly variable. Some years the soil is nice and warm earlier than this, while other times it will be mid-June before the soil gets above 60F. Now I could always buy fungicide-treated seed and plant the corn every year on May 31, but I don't like using fungicides. Instead, I've purchased a soil thermometer. A couple times a week, at about 9AM in the morning, I record my soil temperature. When it consistently gets above 60, I know it's time to sow my corn - especially if the weather forecast is for a nice sunny streak. By doing this I can sometimes get corn started in early May (heck, THIS year my daughter and I went nuts and sowed popcorn on April 29th! We seem to have gotten away with it, at least so far.).

Alternatively you could try the method the Seneca Indians used. When it's comfortable to sit on your bare bottom in the dirt, it's warm enough to sow corn. I might suggest warning the neighbors first, however; and don't forget your loincloth.

Corn needs a relatively high level of nitrogen, and moderate amounts of potassium and phosphorus. Much of its nitrogen needs can be met by growing an overwintered legume cover crop such as vetch or crimson clover. I do like to give my corn supplemental fertilizer, though. Before sowing the seed, I work in about one-half to one cup of cottonseed meal for each 5 feet of row.

Although some people do like the old-fashioned varieties of open-pollinated sweet corn, most prefer the hybrids that have been developed over the past 50 years. Some of you are familiar with the term 'hybrid vigor', which is the innate extra vigor F1 hybrids have when compared to open-pollinated plants. Well, corn could be the poster child for hybrid vigor! Not only are hybrid corn plants markedly stronger, more uniform, and more productive, but also hybridizing has allowed the development of much more tender corn that stays sweet longer.

There have been some additional breeding developments over the past couple decades. Now some corn varieties are available that are extra sweet. These types fall into two groups: Sugar enhanced (often labeled SE or SE+) and supersweet (marked by sh2, which refers to the shrunken kernel size of their seeds). These types start out sweeter, and stay sweeter much longer than "regular" sweet corn (sometimes labeled SU, which I believe stands for sugar unmodified). This longer shelf life is due to a delayed conversion of sugars to starch after the ear is picked. These high sugar types do have a couple drawbacks. They are not as vigorous as SU corn, and so require warmer soil temps for germination - a MAJOR drawback here in the Maritime Northwest. Also supersweets must be isolated from other types of corn; if they cross-pollinate their ears will revert to field corn quality (in a word, yucky).

In my personal opinion the supersweets are much too sweet. I also prefer SU types when I am picking a main season corn; my absolute favorite variety is the "old" hybrid Golden Jubilee. But for early corn the SE varieties are markedly better tasting than their SU counterparts. One way I sometimes get around their need for warm germination temperatures is by starting them as transplants. If you do this, though, note that corn is touchy about being transplanted.

Corn does take up a lot of space! Many people don't grow it for that reason, especially if their garden size is limited. For me, though, nothing really says "summer" like that first barbeque with fresh roasted corn on the cob, straight from the garden to the grill!


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This page was last updated November 18, 2013