Supersweet Corn

For decades, Fedco has been a firm proponent of “eating quality” in sweet corn with flavor, texture and kernel depth as our in-house metrics. We’re a “corny” flavor bunch, dismissing sweetness as the sole measure of breeding progress. Until recently, we hadn’t encountered eating excellence in a Supersweet (sh2) variety. Breeders have now balanced the extra-sweetness with tenderness, creaminess and full flavor. With the sh2 gene, conversion of sugar to starch occurs at a much slower rate, so corn stays sweet long after harvest.

Culture: Supersweet types germinate poorly in cool soils. Wait until soil temps exceed 65° for direct seeding—mid-June in central Maine.

Supersweets require 300' isolation from all other corn types to prevent the kernels of other corns from becoming starchy and tough. If you don’t have space to isolate, choosing a Supersweet means foregoing other sweet corn types.

Sweet Corn at a Glance

Types of sweet corn

Normal Sugary (su): standard varieties with traditional sweet corn texture & flavor. Sugar converts to starch quickly, so eat them within a few days. Tend to have high yields and germinate well in cool soils.

Sugary Enhanced (se): more sugar than su, tender kernels & slightly longer storage time. The * indicates heterozygous (only one parent contributes the se gene); all others are homozygous (both parents se).

Supersweet (sh2): 4 to 10 times the sugar content of su and se. Conversion of sugar to starch occurs at a much slower rate. Stays sweet long after harvest. Extra shriveled seed does not germinate well in cool soil.

Synergistic: more sugar than se. Very tender with long harvest and storage windows. Can be homozygous or heterozygous se with added sh2 kernels.

TripleSweet® Sugary Enhanced: has homozygous se kernels, and 25% of these also contain the sh2 trait.

Corn

• About 85–200 seeds/oz. 1 oz packet sows 25 ft, 1 lb sows 400 ft.
• Seeds per packet vary, open-pollinated selections average 100 seeds/oz, normal sugary varieties 140 seeds/oz, and SE cultivars with shrunken seeds 150-160 seeds/oz.
• Days to maturity are from emergence after direct sowing; for transplants, subtract 20 days.

Culture: Untreated sweet corn seed will not germinate in cold wet soil. Please be patient and wait till soil warms to at least 60° before sowing, or start seedlings indoors and transplant at 3–6" before taproots take off. Minimum soil temperature 55°, optimal temperature range 65–85°. Tender, will not survive frost. Heavy nitrogen requirements. Plant seeds 3" apart in rows 3' apart. Thin to 1' apart. When corn is knee-high, sidedress with azomite or alfalfa meal to stimulate growth. Plant in blocks of at least 4 rows to ensure adequate pollination, essential for good tip fill. If you lack sufficient space for enough plants for good pollination, try hand-pollinating by cutting off the tassels and shaking their pollen onto the silks.

Sweet corn is ready 18–24 days after the first silks show, the exact time dependent on the weather in the interim. Press ears 2" from the tips to assess kernel fullness. Harvest when the kernels are plump, soft, tender and filled with a milky juice. Most sugary enhanced varieties have an optimal picking window of 5–7 days, but some open-pollinated selections hold only 1–2 days.

Corn Insect Pest Control

Corn Earworm
Cultural controls: use resistant varieties with tight husks such as Bodacious RM or Silver Queen, choose short-season varieties, release trichogramma wasps. (Beneficial insects are available at insectary.com or 800-477-3715.)
Material controls: Bt kurstaki, Spinosad.

European Corn Borer (ECB) and fall armyworm
Cultural controls: mow and disk old corn stalks into the soil, release trichogramma wasps (found to give better control than insecticides in research by Cornell’s IPM program on five organic farms) for ECB; none known for fall armyworm.
Material controls: Bt kurstaki, Spinosad.

Flour, Flint, Dent... Corn!

Flour corn has soft starchy kernels easily ground into flour.

Flint corn has hard flinty kernels that store well and is often used to make corn meal, polenta or grits.

Dent corn with indented kernels is eaten fresh as elote or dried and ground into fine cornmeal flour, or used in alkaline cooking processes to make masa, tortilla chips or pozole. (Dent is also most commonly used for processed foods and ethanol production.)

Field corn can be any of the above when used as animal feed, though most typically dent is used. (Also see Field corn from Organic Growers Supply).

Sweet corn first appeared in commerce in 1828 and became popular a generation later. The first crop to be hybridized; most of the open-pollinated varieties disappeared between 1930 and 1970. All sugary enhanced sweet corn traces back to a single inbred developed in the 1960s in Illinois by Dr. Dusty Rhodes, ILL677a. Our trialers have found SE corn to be especially suitable to our climate, with good cool-soil tolerance and a near-perfect blend of sugars and corn flavor.

Testing: To help ensure the purity of our seed, we have for the past seventeen years employed industry leader Foodchain ID (formerly Genetic ID) to test samples of our corn lots for the presence of transgenic contamination. Because of the risks posed by production of genetically engineered Roundup Ready beets, we have added beet and chard varieties to our GE testing program.

We remove any seed lots that test positive for transgenic contamination. A negative test result does not guarantee genetic purity but improves the chances seed is uncontaminated. The tests are expensive, but in a time of genetic roulette they are necessary, though not sufficient. Only if the seed trade takes an adamant position that it will not tolerate GE contamination in products can we maintain any integrity in our seed supply.

Germination Testing

For the latest results of our germination tests, please see the germination page.