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Ask a Master Gardener: Time to plant sweet corn

by Peter Sutter, For the News Tribune | May 10, 2020 at 5:03 a.m. | Updated May 11, 2020 at 10:57 a.m.

Last week, I wrote about the different varieties of sweet corn. I hope you have decided which variety you are going to plant this year because it is time to do so.

According to the University of Missouri Extension's publication 6201, sweet corn can be planted any time from the last week in April to the first of August. Corn is actually a member of the grass family and is best planted after the soil temperature reaches 60 degrees Fahrenheit. Corn planted in cold, wet soil is unlikely to germinate. Corn grows best in air temperatures from 60-95 degrees.

I usually start with the April planting and then plant three successive plantings about three weeks apart. Since our spring has been cooler than usual, I am waiting a little later this year. By doing successive planting, it stretches out the fresh corn harvest. We also freeze some corn for a winter treat, so the successive planting makes that chore a little less daunting when done in stages.

One year, because of persistent spring rains, I ended up planting sweet corn on the first day of August. I will admit I was a little skeptical about planting that late in the summer but had always wondered about it when I would look at the extension's recommendations. Well, it made it, and I had a good harvest.

Another way to stretch the sweet corn harvest is to plant an early, mid-season and a late variety all at the same time. I will warn you though, most early sweet corn grows on short stalks so you will have some bending over to pick your corn.

Once you have selected the variety you would like to plant, sow corn seed 1-1 inches deep. Early-maturing varieties should be planted 8 inches apart, while later maturing varieties can be planted 9-12 inches apart in the row with about 24-30 inches between rows. Corn can also be planted in hills about 3 feet apart, each hill containing three or four seeds.

If you are planting in rows, plant side-by-side to form a block, rather than one long row. This allows better pollination and a fuller ear of corn. I plant four or five rows and make sure the rows are at least as long as the section is wide, forming a block.

Corn grows fast in hot weather and requires an inch of water per week. Avoid overhead watering when tassels appear; water hitting the tassels at the time of pollination can reduce the number of kernels on a cob. Drip or furrow irrigation is best for sweet corn.

Corn is a heavy nitrogen user, so side dress corn with aged compost, compost tea or a high nitrogen fertilizer such as 10-10-10 when stalks are 10-18 inches tall and again when they tassel. Side dressing is putting the fertilizer in the row a few inches from the corn and tilling or raking it into the ground, but be careful not to damage the roots. Corn is shallow rooted so avoid deep cultivation.

As sweet corn grows it will sometimes develop suckers or tillers, which are small stalks that grow out of the side of the main stalk at the base. As a youngster on the farm, I was often given the job of removing the suckers and carried out the practice later in my own garden. I have since learned that these can be left on the plant because they do not reduce yield or harm the plant in any way.

In past years, I have had trouble with the wind blowing my corn over so one important thing you can do to strengthen your corn and make it more wind resistant is to hill up soil onto the stalks when it reaches about 12-18 inches tall. Corn can grow more roots from its lower nodes (or joints), and hilling it up covers those nodes, allowing those extra roots to form. This strengthens it against wind damage. It doesn't make it wind proof, but it sure makes it more resistant to it.

When the silks turn brown and dry up, start checking for readiness. Peel back the shucks of a nice full ear, only far enough to expose some of the kernels. Press your thumbnail into a kernel. When it pops milky white juice, the corn is ready.

It won't all be ready at once. It may take a week to 10 days for all of the ears to mature. If you open the shucks on an ear that's not ready, it's not a big deal. Smooth the shucks back over it and leave it for a couple of days.

The sooner you eat or process sweet corn, the better. Enzymes in the kernels begin converting the sugars into starches as soon as you pick it, and the sweet flavor can fade very quickly, although some varieties claim to keep their "sweetness" longer in storage. Mine never stays in storage long enough to test it out.

Peter Sutter is a lifelong gardening enthusiast and a participant in the MU Extension's Callaway County Master Gardener program. Gardening questions can be sent to [email protected]

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