Corn, Sweet

Zea mays (Poaceae or grass family)

Production

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Soil preparation

• Corn should not follow corn, other grains or cucurbits. 
• Total nutrient uptake is 155 lbs. of N, 20 lbs. of P and 105 lbs. of K.
• Corn does well after a leguminous green manure like sweet clover. But note that early plantings will not be able to depend on the N provided by clover. Nitrogen-fixing bacteria become active when soil is sufficiently warm (over 48°).
• Apply compost and other amendments based on the results of a soil test. Incorporate compost and plant corn in raised beds or on flat ground. 
• Spread lime as needed to increase both the pH and Ca levels. Dolomite lime will also increase Mg levels. Spread gypsum when calcium levels are low but pH is correct.
• Sweet corn can be planted through a rolled and crimped cover crop like vetch or Austrian winter peas. To ensure good weed control, plant the vetch in early September of the previous year at a rate of 40 lbs. per acre, or the peas at a rate of 200 lbs. per acre. Fertilize to provide nutrients for both the vetch and the sweet corn at that time (based on the results of a soil test). To properly kill vetch or Austrian winter peas, use a no-till planter (without seed in the box) and slice the over crop with the coulters of the drill. Additional N for corn will be based on the results of a pre-sidedress nitrate test (PSNT).

Common recommended fertilizer rates¹

Nitrogen	Phosphorus	Potassium	pH
140	0-160	0-160	6.2-6.5
1Rates are for New York and are from Cornell University’s Nutrient Guidelines for Commercial Vegetable Production (2019). Check the Cornell website for updated guidelines, or consult with local experts for recommended rates outside New York.

Varieties

• Wisconsin variety trial
• New York variety trial
• Sweet corn varieties are listed as either standard sugary (su), sugary enhanced (se), shrunken-2 or supersweet (sh2), augmented supersweet (shA), or synergistic (syn). Augmented supersweet varieties with good flavor include Mirai types and the XtraTender series. Unfortunately, birds love these too. There are many good organic corn varieties on the market, including Double Standard, Allure and Enchanted.
• Robust is a good variety for popcorn.

Direct seeding information

Seeder	Rows	Seeds per foot	Seed plate no.	Depth (inches)	Sprocket setting	Notes
MaterMacc	2	6	24 H 4.5	1	22-17	Soil temperature should be at least 65° for se and sh2 untreated varieties.
Jang	2	6	A6 AA6, or N6		Front 13/rear 10	With shrunken seed, it’s difficult to find the right adjustment for effective singulation.

• You can also use an Earthway seeder for direct seeding. Use the corn seed plate or smaller when planting shrunken seed.
• Direct seeding within organic guidelines often results in poor stands. Poor stands cause poor weed control and poor yields. Therefore, many organic growers prefer to transplant sweet corn.
  

Greenhouse guidelines

• Seed corn in cell-pack trays 2 weeks before transplanting. To increase transplanting speed, plant 2 seeds per cell. This allows you to plant 2 plants in 1 cell at 14–16 inches apart. The objective is to have a population of 24,000 plants to the acre for irrigated sweet corn. Not every cell will have 2 plants. Adjust your in-row spacing based on your wheel track spacing (60 or 72 inches). Adjust your numbers downward when planting non-irrigated sweet corn.
• Place the trays on wire benches to achieve proper air pruning. Sweet corn has a very aggressive root system. 
• Alternatively, use a paper-pot system using a 6-inch spacing with 1 seed per pot.

Cell pack tray	Germination temp	Growth temp	Hardening off	Cell pack tray
72, 98 or 128	70°–95°	65°	Withhold water	Plant 2 seeds per cell. Put plug trays on a wire mesh bench to encourage air pruning. Move outside 3 days before transplanting.

Number of successions

• Seed the first sweet corn 2 weeks before it can be planted in the field. This date can vary depending on whether you plan to provide some frost protection. Medium-weight row covers (0.56–0.9 oz per square yard) can protect crops against 26°–28° nighttime temperatures. 
• Be aware that protecting sweet corn with a row cover will also decrease the days to maturity, so you’ll need to cover the next succession as well or seed it less than a week after the first planting. 
• If you’re not using row covers, plant the second succession 2 weeks after the first planting. Reduce seeding time by 1–2 days until you’re on a weekly schedule.
• In the northern United States, corn earworm becomes too difficult to control organically, so the last seeding date for 75-day corn falls around the end of July.

Signs to watch for and what to do

• Harden plants outside for a few days. Plants that are lush don’t perform well in the field.
• Don’t grow tall transplants.

Transplanting tips

• Transplant as soon as plugs pull well and stay together. If roots are tangled to the bottom of the tray (a result of poor air pruning) you’ll need to cut them or pull them out straight so that they don’t interfere with planting.
• When using paper pots, transplant in the field before seeds have germinated, or immediately after. Once the corn is up, its root system starts branching on the bottom of the paper-pot tray. Air pruning isn’t possible with paper pots. The other disadvantage of planting corn using a paper-pot system is when birds try to dig up the young plants: They will pull not just 1 plant at a time, but a chain of paper pots.

Transplanting in 5- or 6- foot raised beds

Rows	In-row spacing	Planting depth (inches)	Notes
2	14-16 inches	As deep as possible	Use this in-row distance when seeding 2 seeds per cell. Transplanting works well with a carousel transplanter; planting by hand or using a water-wheel planter might not be economically viable.

Planting procedures

• Adjust mechanical transplanters so there is good contact between the plug or root ball and the soil. Ensure plants are properly rooted before cultivation.
• Isolate your supersweet corn varieties from non-supersweet varieties by at least 300 feet to avoid cross pollination. Cross pollination will cause tough, starchy kernels in both types. If this isn’t possible, make sure your other varieties have a day-to-maturity difference or planting date difference of at least 12 days from the supersweet varieties. 
• For corn in general, plant in blocks of at least 4 rows to ensure good pollination.

Cultivation procedures

• Your first pass will be different based on whether you’re transplanting or direct seeding the corn.
  • Transplanting: Use side knives with a torsion weeder (if possible) in combination with a finger weeder 7–10 days after transplanting, or as soon as possible without damaging the plants. Alternatively, use a tine weeder, but be careful to avoid uprooting plugs. 
  • Direct seeding: Use a tine weeder when weeds are in the white thread stage. You can use the tine weeder before the corn has emerged as it forms a strong root system before it spikes.
• Hand hoe between plants as necessary.
• Use a finger weeder in combination with side knives for a second pass when new weeds emerge. Move finger weeders away from the crop if they cause damage. Alternatively, if you want very slight hilling, use spring hoes in combination with side knives.
• If a third cultivation is needed or possible, use Lilliston rolling cultivators and hill aggressively without burying the plants.

Frost, insect and nuisance animal protection

• Corn rootworm is an issue when corn is direct seeded. Transplanting is a good remedy. 
• You can prevent cutworms by spraying the soil with the beneficial nematode Steinernema carpocapsae. Once the pest is in the crop, control the population by spraying the crop with Bacillus thuringiensis kurstaki, or spread a baited product containing spinosyn, like Seduce, around the plants.
• European corn borers (ECB) can be controlled with a spinosyn-based product, like Entrust, or with Bacillus thuringiensis, as in Bt kurstaki. Spraying is cost effective when you meet a threshold of finding more than 10 moths per day in a pheromone trap. Other means to observe ECB presence are small pin holes on the leaves—referred to as shot hole injury, these holes tend to line up perfectly horizontally—or broken off immature tassels. These last 2 methods are unfortunately too late to obtain good control, as the first application should be when corn is in the whorl stage. Repeat application 3–5 days later to ensure coverage of all emerging tassels. Use high pressure (150 psi) to provide good penetration. As spinosyn-based products kill many beneficial insects, including bees, spray it only very early in the morning or later at night when insects are less active.
• Alternatively, use releases of Trichogramma ostrinea, a parasitic wasp. You can get excellent control of ECB when their pressure is low. The key is to introduce wasps to the field when the corn is knee high. Releasing 30,000 eggs per acre for about 3 weeks has been proven to yield better results.
• For corn earworm, use a product containing the nuclear polyhedrosis virus, as in the biological control product Gemstar LC, at the recommended rate. Alternatively, apply Gemstar or Bt kurstaki to individual ears using a Zealater applicator. Adding an attractant like molasses and milk will increase the effect.
• Gemstar provides some control for fall armyworm, but apply Bt kurstaki or Entrustin case of an outbreak.
• Put up an electric deer fence to prevent them from eating the silk. Silk damage results in an unmarketable ear, as each piece of silk will create 1 kernel. To prevent deer damage, build a temporary fence using 4-foot fiberglass posts and attach 1 clearly visible wire like IntelliTape at about knee height. Build a second fence inside the first fence, but attach 2 wires or twine whereby the top line is about 7-feet tall. Deer don’t have very good depth perception and won’t attempt to jump this fence without checking out the first fence, so electrifying the second fence is often not needed. Bait the outside deer fence with peanut butter and electrify it. Make sure you build the fences, bait and electrify on the same day. The surprise effect is what matters most with this particular deer control.
• For raccoon control, use a separate electric fence when corn has visible ears. To get effective control, only use a high-voltage fence charger suitable for nylon woven wire.
• For bird control you can use an electric sound deterrent system, such as Bird Gard, which produces the distress calls of certain birds and the watch calls of predators. In extreme cases you can use a propane-fired bird cannon that produces a blast at set intervals. Neither is effective long term as birds get used to the sound. Balloons can be effective but need to be taken down each time you use the boomsprayer. Some people have effectively used lasers designed for bird control, which has become more cost competitive over the years.

Other cultural practices

• Irrigate frequently for optimum yield and plant health. Frequency depends on soil type, evaporation, precipitation and the particular needs of the crop. 

Double cropping and/or cover cropping

• After harvest, mow and incorporate corn to reduce future ECB infestations. No-till planting of cover crops isn’t advisable as ECB will overwinter in the corn stalks. If you want to lay plastic mulch during the following season, make sure you carefully shred the corn stalks before planting a cover crop. Sharp corn stalks break down slowly and can poke holes through the plastic mulch.
• Corn that was planted later can be followed by rye and vetch.

Additional resources

• Organic Insect Management in Sweet Corn

Harvest

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Yield	Ears are often packed in 48-count boxes. Excellent yields are up to 200 boxes per acre when management practices are optimal (e.g., planting, fertility, irrigation and weed control). Most organic farmers report a yield of 150 boxes per acre.
Standards	Harvesting1 When using a harvest conveyor, the rate is 8–10 bins (400–500 ears) per hour per person. When harvesting by hand with a pickle barrel, time is lost unloading the pickle barrels into boxes, but time is gained by freeing up a tractor operator. Hand harvest is also harder on your workers. Using a harvest conveyor requires 6 people: 1 person on the tractor, 1 person on the wagon and 4 people harvesting.
Tools and supplies needed	Large 1 ¾-bushel boxes and either a harvest conveyor or pickle barrels.
1Harvest rates don't include the time required to transport crops from the field to a wash and pack shed or storage facility.

Ready-to-harvest and quality indicators

• Ears are firm and filled out to the tip with no missing kernels; husks look fresh and the silk sticking out of the ears is brown and dead but not eaten by insects or deer. When husks are pulled back, all kernels are plump and tender.
• Don’t harvest overmature ears, as the sugars have converted to starch.
• Don’t harvest ears with worm damage, damaged husks or missing kernels. To check for incidental worm damage in the field by harvesters:
  • The European corn borer can be detected by a pin hole in the ear and can be felt when pressing the ear in the palm of your hand. The presence of this worm is noticed by a hollow feeling underneath the leaves where it has damaged the ear.
  • The corn earworm is usually at the tip of the ear and is easier to spot. Fall production in southern states is particularly challenging due to high worm pressure.

Harvest procedures

• Wash hands before harvesting sweet corn.
• Harvest in the morning hours to avoid field heat accumulation.
• When harvesting by hand:
  • Take 2 rows and put a pickle barrel into the middle.
  • Grab the ear and pull down and out to pull the ear off the stalk.
  • Remove extra stem at this time, or do it when transferring the corn into the boxes.
  • Remove stems both to save space in the box and for its cosmetic value.
  • Count 50 ears to a barrel to allow for easier sorting at the packing shed.
• If using a harvest aid conveyor, place the ears on the belt as you pick. The person on the wagon counts the corn into boxes. For 50 ears, pick up 4 ears at a time and count to 12 and then add 2 individual ears to get to 50.

Sorting procedure

• Wash hands and rinse boots before entering the wash-and-pack shed, and cover up field clothes with a bib. If a long-sleeve shirt contains soil, remove this as well.
• Sort all the ears in a well-lit barn so that it’s easier to identify defects such as worm damage or poor tip fill before distribution. Also, remove extra stem and flag leaves.

Additional resources

• Wholesale Grading and Packing Instruction Sweet corn
• Production Guide for Storage of Organic Fruits and Vegetables

Packing and storage summary for sweet corn

Cleaning in the field	Remove extra stem and flag leaves if possible.
Packing in the field	Pack 50 ears in a large plastic 1 ¾-bushel harvest box. Picking extra ears allows for sortout in the packing shed.
Packing for delivery	Ears are inspected, sorted, recounted into 48 ears and placed in clean delivery boxes, crates or bags for wholesale or CSA delivery. If the 50 ears per harvest box creates a surplus or deficit with this final sortout, then adjust the amount you harvest next time.  See the International Federation for Produce Standards for the correct PLU code. Add the prefix 9 for organic crops.
Storage	At 32°–34° and 95–98% humidity. Pack with ice in closed containers or bags for storage that lasts longer than a few days.

This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture through the Sustainable Agriculture Research and Education (SARE) program. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.