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Choosing Sweet Corn Varieties

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By Dusty Hancock 

Master Gardener℠ intern in Chatham County

Su, Se, Sh2, Syn? C’mon I just want fresh corn!

Who doesn’t like sweet corn? The fresher the better. How better to get it at its finest than to gather from your own corn plot? It isn’t overly hard to grow, but be forewarned there are plenty of four-legged bandits who will desire your produce as much as you do so give some thought to protection.

I had a plot once that was just coming into season. I figured there was a minimum of 200 ears of organic goodness just days away from the table and freezer. I had in place a good electric fence setup that had kept the varmints away in the past. But they were watching my crop closer than I. My earth ground had gone dry and they knew it before I did. I woke up one morning to corn cobs scattered all down the lane, in the trees, and in the creek. In one night, the masked bandits had held a smorgasbord in my corn plot and there could not have been a hungry coon left in a one-mile radius. So forewarned is forearmed!

Master Gardener Volunteer Dusty Hancock

This Hoosier knows corn!

Assuming you are better prepared than I was, all you have to do is pick a variety and start planting in your prepared plot. If only it was that easy to make an informed choice on variety. No seed packet says this corn is terrible, don’t plant it. Nope, everyone says theirs is the sliced bread of seed corn, so that doesn’t help. But if you know the code of all the initials and understand the other info on the seed packet it isn’t so bad. Consider the following factors to make sense of different sweet corn varieties.

How sweet do you like your corn? Old timey flavor or like candy? How long do you need it to stay at prime condition for eating or freezing?

Su (standard) varieties have  around 5-16% sugar content, imparting a classic ‘old timey’ corn flavor you may remember depending upon your age. The sugars convert to starch rather quickly so shelf life is reduced. These corn varieties may be hybrids, but many are open pollinated or heirloom,  meaning you can save some of your corn from the year before to plant the next year.

Se varieties have between 14 and 35% sugar content. These sugar enhanced hybrid corn varieties have increased tenderness and sweetness compared to Su varieties. They also have a longer shelf life (typically 4-6 days when stored at 34-40℉). Since Se corn varieties are a hybrid of other Se varieties and Su varieties, the seeds do not breed true, so saved seeds will not exhibit the same characteristics as the mother plants.

Se+ varieties are the result of hybridizing (traditional cross breeding, not GMO molecular breeding) two Se parents (called homozygous corn). These varieties are sweeter yet!

Sh2 varieties have between 28-44% sugar content and may also be called supersweet corn. The Sh refers to the appearance of the kernels when dried and these varieties are the the sweetest and have the longest shelf lives (typically 9-10 days). These are again hybrids, so no seed saving here. However, they do need to be pollinated by the same variety to impart all of the beneficial characteristics, so make sure plantings of these varieties are isolated from other varieties spatially (at least 25 feet) or temporally (a few weeks).

Syn is a newer hybrid that contains genes from su, se, and sh2 varieties, giving  syn corn the tenderness of the se and the shelf life of the sh2 varieties. Tender, supersweet and long shelf life is a combination that sounds more like a confection than a vegetable! You need to let kernels plump out before picking and keep isolated from other types of corn just like the sh2.

Organic or non-organic?

This doesn’t refer to being genetically modified by molecular breeding, but to the inputs that went into your packet of seed. Organic seed is raised with very tight regulations in regards to the fertilizers and insecticides/fungicides allowed during its growth and subsequent processing. Organic seed loses that classification if it is treated with a fungicide to minimize seed rotting that can occur if planted cool, moist soil.

While it never hurts to start off organic, unless you intend to also maintain those same organic restrictions in your plot there should be little hesitation in planting treated non-organic seed. Treated seed will help you get into the soil earlier and perhaps avoid some of the diseases and insect damage that occurs later in the season.

Do you prefer white, yellow or bi-color corn?

Other than visual appeal, the sugar type determines the flavor, not the color. Yellow sweet corn has actually only been commercially available since the early 1900’s. Rumor has it that the desire was to make it look pre-buttered right out of the husk! Gotta admit a big yellow ear does indeed start your mind thinking in that direction.

Short or tall plants?

If you are planting in a windy area think about plants that are more in the 5 ft range versus the 7 footers. Planting in blocks helps slow down wind damage and is needed to improve pollination. Open pollinated corn will not be as uniform in height or maturity dates and will require a bigger block of at least 5 to 6 rows to pollinate. Hybrids will be incredibly uniform inside the variety and can be planted in slightly smaller blocks with a minimum of 4 rows. Never plant 1 or 2 long rows and expect to get anything close to a desirable ear.

What level of disease resistance can you get?

There are numerous wilts, blights, viruses, smuts and insects that can affect your crop. Most hybrids have been developed with some level of protection against the more common maladies. The corn earworm rarely destroys whole ears but certainly decreases the yield on each affected ear. Tight husks are good protection and if you are really zealous you can place a couple of drops of mineral oil at the tip of the husk where the silks are. Wait at least 2 days after the silks have totally emerged to keep from hurting pollination. Take that you stinkin’ caterpillars!

A really good way to answer a lot of these questions is to try different varieties typically found at Farmers Markets. The seller will usually be happy to share the type and variety they are offering. It will give you a start at answering the questions above and making a selection to start with. Understand that each plot has different soils and microclimates so you may need to experiment for a few times to find the right corn for you.

I typically plant three varieties each year, two that I know have done well in the past and I can depend upon for output and one variety to experiment with. If the experimental variety does better than one of my BIG 2, I try it one more year to make sure it wasn’t a fluke. If it does better again, this new variety replaces the worst performing old variety in my BIG 2 and I repeat the process the next year.

Follow the planting instructions that come with your seed but generally I plant treated seed about 1.5” deep on 12” centers with the rows about 28” apart. Some people prefer to overplant and plant corn every 6 inches and thin it out after it sprouts to avoid having empty spots in their rows if germination goes poorly. I prefer to wait until the soil temperature 2” down is at least 65℉ to help ensure that doesn’t happen and I don’t waste seed on plants I am just going to throw away. I plant in a minimum block size of 5 rows a minimum of 12-15 feet long. Plant on a weekly basis if you want to extend your picking or to keep one variety from pollinating another.

The soil pH should be between 5.5 and 7 and well drained or at least they shouldn’t have their feet standing in water all season. While the plants are young keep the weeds down, but the corn will begin to shade them out as it gets bigger. In an ideal situation you would like to have about an inch of water a week during the growing season. Look for the silks to appear (not the tassel at the top) and count down approximately 20 days for ear development. You should feel the ear swelling in the husk and when you can’t stand waiting anymore, pull back a husk and press your fingernail into a kernel. If you feel a little resistance and then the kernel burst, yielding its sugary delight, start picking!

Or you can wait for the bandits to pick your crop for you if you can’t figure out when it is ripe. They know, believe me they know…