Grow Successful Sweet Corn

Reader Contribution by Pam Dawling
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Our third, fourth and fifth plantings of sweet corn and our irrigation sprinkler.Photo by Bridget Aleshire. 

Caring for Your Sweet Corn Crop

Sweet corn needs hoeing and weeding at least twice, once two weeks after sowing, and once at four weeks. Even better are four rounds: at 7, 14, 21 days (when the plants are 6-12” (15-30cm) tall) and finally one around 35 days when they are 18-20” (45-50cm) high. We use a walk-behind tiller, and follow up with hoeing and thinning. A wheel hoecan be a great tool for this job if you don’t have or want a rototiller.

Never allow soil in corn plantings to dry out. At tight spacing this becomes very important. You might need more than 1” (2.5cm) per week for maximum productivity, although corn is more drought tolerant than some crops. The most important times for watering are silking (when the silks first become visible outside the husks) and while the ears are filling out.

Flame-weeding can be used after planting before the corn emerges, or after the crop is 2” (5cm) tall, using a carefully directed flame. Consult ATTRA Flame Weeding for Vegetable Crops

People used to recommend removing the suckers that came from the base of the plant, thinking it led to higher yields. This idea has been tested, and in fact it can damage plants and possibly even reduce yields.

Undersowing Cover Crops in Sweet Corn

Another practice that has been shown to lower yields rather than raise them is planting into strips tilled in a white clover living mulch.  Jeanine Davis addresses this in NCSU’s Organic Sweet Corn Production.The clover can out-compete the corn, become invasive and hard to get rid of. Soil temperatures will be lower (a disadvantage in spring) and slugs and rodents may increase.

A more successful practice is sowing a cover crop into the corn 28-35 days after emergence. We undersow with soybeans (oats and soybeans for our last planting). Although soybeans don’t supply the highest amount of nitrogen compared to other legumes, soybeans are cheap, quick, somewhat shade tolerant and can withstand the foot traffic during harvesting. Other growers sow forage brassicas. Research has shown that this does not depress corn yields. The brassicas can be harvested for forage after the sweet corn harvest is finished. Undersowing with white clover is also possible, if you can leave it to grow after the corn is finished.

Harvest Sweet Corn All Summer

In order to have a continuous supply of sweet corn all summer, a bit of planning and record-keeping is called for so that each year’s plan can be fine-tuned. The easy and approximate method of getting a good supply is to sow more corn when the previous sowing has 3-4 leaves, or is 1-2” (2.5-5cm) tall. That will be about every two weeks.

For fine-tuning for the most even supply, nothing beats real information about what happened, written at the time it happened. We have a Planting Schedule on a clipboard in the shed, and we write down actual sowing dates (next to the planned sowing date), and harvest start and finish dates. See Growing sweet corn for the whole summerto read about the Succession Planting method to calculate best planting dates and intervals for a continuous supply. We make six plantings: 4/26, 5/19, 6/6, 6/24, 7/7 and 7/16, to provide fresh eating every two weeks. The planting intervals are 23, 18, 18, 13, and 9 days.

By planting three varieties each time, we get new corn coming in three times during each two weeks. Sow varieties with differing days to maturity. We sow Bodacious (77 days), Kandy Korn (89 days) and Silver Queen (96 days) on the same day, and get over two weeks of harvests.

Silver Queen sweet corn almost ready to harvest. Photo by Kathryn Simmons

Early Maturing Sweet Corn Varieties

Remember, if you decide to grow several kinds, not to mix Sh2 kinds with anything else, or everything will taste starchy. For more on this, see my previous article Growing sweet corn for the whole summer.

Early Maturing Sh2 Varieties: The Supersweet corn varieties are where most of the attention goes these days, and bicolor is preferred. In order of maturity (speediness in ripening): Catalyst XR (bicolor, 66days); Sweetness synergistic (bicolor, 68d); Kickoff XR (bicolor, 69d); Temptress synergistic (bicolor, 70d); Xtra-Tender 2171 (bicolor, 71 d); Nicole (white, 72d); Xtra-tender 20173 (bicolor, 73d); Signature XR (bicolor, 73d); Anthem XR (bicolor, 74d); Natural Sweet Organic (bicolor, 74d); Xtra-tender 3473 (white, 75d); SS2742 (Bicolor, 75d)

Early Maturing SU Varieties: Among yellow SU cultivars, Earlivee is the earliest to mature, at 58 days, and Seneca Horizon matures in 65 days. Sugar Pearl at 73d is the earliest white cultivar to mature. Quickie, at 64 days, Double Standard (OP, 73d) and Butter and Sugar at 73 d, are the earliest bicolor cultivars to mature.

Early Maturing SE Varieties: Among yellow SE varieties, Precocious and Spring Treat mature earliest, at 66 and 67 days, respectively. Bodacious (yellow, 75d) is well worth the wait! Of white varieties, Spring Snow, at 65 days, is the earliest to mature. There are no bicolor SE varieties.

Early maturing SE+ varieties: Sugar Buns (yellow, 70 days); Trinity (bicolor, 68d)

Pests and Diseases of Sweet Corn

Crows and other birds can be troublesome, removing the seed before it even grows. We leave the row-marking ropes in place after sowing. Bird-scaring flash-tape may be even more effective. Rowcover would also work.

Some say interplanting corn with big vining squashes deters raccoons and other critters, but I think it deters people too!

There are several caterpillar pests. An integrated organic approach to keeping pest numbers below economically damaging levels includes crop rotations, tillage, choosing resistant or tolerant varieties, encouraging beneficial insects, and ensuring adequate fertility and water. The next step is to scout for pests regularly, and take action as required.

Corn Ear Worm (CEW) is the most common pest. There may be six generations a year in the South. These caterpillars can bite – it’s just a nip, but can be a shock! A first line of defense is to choose varieties with tighter husks, which are harder for the worms to get into (Bodacious, Tuxedo, Silver Queen). Natural predators can be encouraged by planting alyssum or other small, open-flowered plants. You could buy Trichogramma wasps.

Caterpillars can also be dealt with putting a few drops of vegetable oil in the tip of each ear. Mixing with Bt gives better results, when applied 2-3 days past the full-brush stage of silking. . The Zea-later was a tool developed for applying vegetable oil in the tip of each ear, mixed with Bt, 2-3 days past the full-brush stage of silking. Unfortunately the treatment caused pollination problems at the tip of the ears, and so it has fallen out of use. If pest numbers are not too high, you can simply cut or snap the ends off the ears.

European Corn Borer (ECB) drills through the whorl of leaves of the young plants, leaving a pattern of large holes as the plant develops. Bt and Spinosad will kill these, as will Trichogramma wasps. To reduce damage in future years, be sure to mow and disk old corn stalks into the soil at the first opportunity. Organically farmed soils have less of a problem with ECB.

Fall Army Worms (FAW) are also killed by Bt and Spinosad. These three pests (CEW, ECB, FAW) can be monitored in a single program, starting when the corn plants are at the whorl stage. At that point, scout for FAW, and treat if more than 15% of your plants are infested. At the pre-tassel and tassel stage scout for ECB and FAW. If infestation exceeds 15%, make a foliar spray with Bt or Spinosad. Check again in a week and repeat if needed. Then at the early silk stage, look for CEW and if needed, inject oil in the tips. If you also see ECB moths, apply Bt or Spinosad.

Cutworm can be a problem following sod, or if there are adjacent grassy areas. Bait them with bran, cornmeal and hardwood sawdust mixed with molasses and water – these baits swell inside the pests and kill them. For more effectiveness, add Bt to the mix.

Corn Rootworms are best controlled by rigorous rotations. Spotted cucumber beetles are the adults of corn rootworms.

For a more complete description of corn insect pests, see the 2004 Organic Insect Management in Sweet Corn by Ruth Hazzard & Pam Westgate. It includes good photos of the beasties. Cornell has a good Resource Guide for Organic Pest and Disease Management. Search under Crop Management Practices for Sweet Corn.  Be aware of the updated info on the pollination issues with applying oil in the ear tips, since these publications came out.

Corn Smut fungus (Ustilago maydis), known in Mexico as Huitlacoche, is edible at the stage when the galls are firm and tender. The flavor is sweetish. Silver Queen is the variety “best” at producing this fungus, should you wish to grow it. We carefully harvest the infected ears (or pieces of stem) into a special Smut Bucket, trying not to scatter the spores. Because none of us like this delicacy, we take it to the compost pile.

Our first harvest of sweet corn (Bodacious). Photo by Pam Dawling

Sweet Corn Harvest

Harvest corn before daybreak for best flavor, because the sugars manufactured in the plant the day before become concentrated during the night. Harvest may start 18-24 days after half the ear silks show, if the weather has been reasonably warm. Judging corn’s ripeness is a skill, based on information from many of the senses.

The first sign we look for is brown dead silks. If the ear has passed that test, we investigate further. All ears should look and feel plump and rounded to the tip. Each variety is a little different, so close attention is needed. Some varieties exhibit “flagging” of the ear, meaning it leans away from the stalk as it matures and gets heavier. New crew can test for ripeness by opening the side of the husk with thumb nails, and puncturing a kernel: the kernels should look filled-out and rectangular, not round and pearly; the juice should be milky, not watery or doughy. The advantage of opening the side of the husks is that it is possible to close the gap if the ear is not ripe, without risk of collecting dew or rainfall. If the ear is ripe, we bend it downwards, give it a quarter-turn twist, and then pull up away from the plant.

Harvest every day or every other day. Leaving a three-day gap risks poor quality starchy ears and a lower total yield. After harvest, refrigerate the corn quickly, and keep itcool until it reaches the boiling water.

Some of this information comes from my book, Sustainable Market Farming.

Another good resource is ATTRA Sweet Corn: Organic Production 

In July 2014, I wroteGrowing sweet corn for the whole summer.

Pam Dawling works in the vegetable gardens at Twin Oaks Community in central Virginia. She often presents workshops at MEN Fairs, as well as sustainable agriculture conferences. Pam also writes for Growing for Market and other magazines. Her books, Sustainable Market Farming, and The Year-Round Hoophouse are available at www.sustainablemarketfarming.com.Her blog is on her website and also onfacebook.com/SustainableMarketFarming.


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