Q: We bought some early sweet corn from the farmers market. It was the sweetest I have ever eaten. I want to grow some in my garden next year. The lady at the market didn’t know what kind it was. Any ideas on what to look for?
A: In the case of many garden plants and sweet corn in particular, a great deal of work has been done to produce new varieties that have better-tasting characteristics. This work has been going on for decades and even centuries.
Corn plants produce seeds with a high starch content so that the germinating seed can use it for its initial growth. The seed converts simple sugar compounds into complex starch molecules. The starch is good for cattle and people to eat, but people prefer sweeter foods whenever possible.
Back in the early 1800s, sweet varieties of corn began being sold. They were created when a single recessive gene displayed its characteristics. It caused the seed to slowly convert its sugar into starch while on the plant, but as soon as the ear was picked, the seeds began losing their sweetness. So, if you could harvest it and eat it that day, you were OK. These corn plants are known as sugary hybrids and are often designated as “SU hybrids” on seed packages or in catalogs.
Back in the 1950s, another recessive gene was brought out through hybridizing. It is called the shrunken-2 gene and is designated “Sh2.” The seeds are very wrinkled when they are dried for storage. These seeds are very slow to turn sugar into starch before and after harvest. Unfortunately, they also have very tough skins that make them a little less tender to eat—or on the positive side, it can be called a crisp texture. These hybrids from the University of Illinois are often called “supersweet,” and the sugars last about five days after harvesting.
In the 1960s, a new gene was discovered called the sugary-enhanced gene. The SE hybrids have the highest sugar content, and they last the longest after harvest—for more than a week if refrigerated. The kernels are tender enough to be called creamy. Nothing was manipulated in a laboratory to enhance the seeds.
All sweet corn varieties need to be planted away from popcorn, ornamental corn and field corn. The pollen from these other types of corn will turn sweet corn starchy instead of sugary. The shriveled seed characteristic of sweet corn will shrivel popcorn seeds so they may not have enough moisture to pop. The yellow color of corn will cause any white corn pollinated to become yellow.
There are new varieties that have one or more parents or grandparents that have the SE gene, so some or all of the kernels are sweet, but they are not as sweet as the Sh2 varieties. The SE hybrids have a tender skin, germinate well and don’t have to be isolated from other varieties.
If you intend to grow some of these newer varieties in your garden next year, here are some tips: The shriveled seeds of some of the new varieties need to be planted shallower, and they will need more water. The soil should be lighter with less clay, and it needs to be warmer, so plant them in full sun. They are harder for the seller to keep dry and disease-free, so expect them to cost more.
Most grocery stores won’t be able to tell you the variety of sweet corn they sell, but many farmers market vendors will be able to tell the variety if not the designation. The main thing to remember about fresh corn on the cob for the summer picnics is to eat it as soon as possible after harvest. Even the sweetest varieties are changing sugar into starch from the moment they are harvested.
