Cultural Practices

Soil Fertility

Apply lime according to soil test to maintain soil pH between 6.5 and 6.8.

Less nitrogen fertilizer will be needed if legume sod was plowed down or if manure was applied (see Table 1, page 2 and Table 7, page 15). 

Apply no more than 80-100 pounds per acre combined weight of actual nitrogen and potassium applied 2" on the side and 2" below the seed as a band. Higher amounts of nitrogen and potash applied as a concentrated band may damage corn seed and young plants.

Plant Nutrient Recommendation According to Soil Test Results for Sweet Corn
SWEET CORN Nitrogen (N) Lbs per acre

   Phosphorus (P) Lbs P2O5 per acre

   Potassium (K) Lbs K2O per acre

Soil Test Results   Very Low Low  Optimum Above Optimum Very Low Low  Optimum Above Optimum
Early Season Sweet Corn                  
Broadcast and Incorporate 0 100 40 0 0 150 90 0 0
Band Placement at Planting 40 40 40 40 0-40* 30 30 0-30 0
Sidedress 60-90** 0 0 0 0 0 0 0 0
TOTAL RECOMMENDED 100-130 140 80 40 0-40* 180 120 0-30 0
*Phosphorus is not necessary for warm soils.
**Before sidedressing use a nitrate test to determine the need for additional N

Planting

Effective isolation is required in some cases with the present types of sweet corn on the market. Isolation is affected by distance, wind direction, time of pollen shed and silking, and blocking. From a practical standpoint, the same methods are needed as when separating white and yellow varieties. Field experience indicates isolation can be managed more easily than initially expected.

Plant early varieties 8"-10" apart within rows with 30"-36" between rows. Plant main season varieties 10"-12" apart within rows with 36" between rows. This requires 10-15 lb of seed/A (1-2 oz per 100 feet of row) or 17,500-26,000 seeds/A for early and 14,500-17,500 for main season varieties. Match seed size to seed plate. Read seed container or contact the company regarding appropriate plate sizes. 

First plantings are made in early April in southern New England and in May in northern New England.  Growers planting in cold soils run the risk of erratic germination and poor stands.  Avoid planting while soil temperature is lower than 55° F.  If soil temperature is below 60° F, it is advisable to plant treated seed.  If you are planting untreated seed, wait until the soil temperature is at least 65° F.  Most seed companies perform cold germination tests of their seed.  If in doubt about the suitability of a corn variety for early planting, ask your seed dealer about the low temperature germination and vigor of the seed. 

Clear plastic mulch raises soil temperature and can be used for the earliest plantings.  This can allow for earlier planting and provide corn 7-10 days earlier than non-mulched corn.   Apply fertilizer and herbicides, and plant seed before laying the plastic over seeded rows.  Two rows 18"-24" apart are usually planted under each strip of 5 ft-wide plastic.  To avoid plant injury, do not let temperatures beneath the plastic get too high (90° F or more).  When such conditions occur, or when the plants reach 4" in height, cut slits in the plastic to allow heat to escape and plants to grow through.  Remove the plastic completely by the time the corn is knee high to facilitate removal and permit cultivation.

Spunbonded row covers offer a potential three-way benefit for early sweet corn production.  Maturity is increased by 5-10 days, yields are generally increased by 15%-20%, and the first generation corn borer can be controlled if the covers are left on until after the peak of the first generation corn borer flight.  They can also be used to pre-warm the soil before planting.  They can be removed to allow planting and then replaced.  Weight cover edges with soil or sand bags to prevent damage by gusty winds, but leave adequate slack for plant growth to the tassel stage.

Transplanting Sweet Corn

Transplanting sweet corn offers some advantages to growers over direct seeding, including better stands, earlier harvest, and less dependence on pre-emergent herbicides.  However, transplanting is more labor intensive, costly and requires attention to detail in order to be successful.

Corn can be seeded by hand, or a simple, inexpensive drop seeder can be built to fit the size of tray to be used.  98-128 cell trays work best (a 128 cell tray requires 82 trays per acre).  The smaller plug trays require less media, but are more easily root-bound. Fill trays with a peat-based potting mix, and plant one or two seeds per cell.  Place trays on tables or benches to prevent plants from rooting in the ground.  Greenhouse temperatures should be set for 65-degree days and 60-degree night temperatures. Transplants should be ready in about 14-18 days, and should be hardened off before planting in the field, by placing the trays outdoors and limiting water for a few days.  Fertilizer should be banded prior to planting, or applied as a liquid at planting.  The plants should have good, cohesive roots that come out of the tray with relative ease. They may be planted by hand or machine.  Plants can be spaced 14-16 inches apart within rows, with about 3 feet between rows.  Floating row covers should be placed over the corn for the first two to three weeks after planting.  These can be pulled back to allow cultivation.  Transplanting and row covers should bring corn to maturity about two weeks earlier than direct seeding.  Not all varieties perform well in this system.  Test your favorite early-mid maturity varieties in small trials before committing large amounts of trays and greenhouse space to them. 

Harvesting and Storage

The sweetness and tenderness of sweet corn will deteriorate rapidly after harvest. Sweet corn should be cooled immediately after harvest and kept at 32º F to retain optimum freshness. The crop is best harvested early in the morning when there is less field heat. Harvesting at the proper stage (milk stage) is critical in maintaining quality. During the summer, sweet corn will be at the proper stage only 1-2 days. It will approach maturity 16-22 days after silking and should be picked daily. As the kernel passes the prime harvest time, sugars convert to starch and the pericarp becomes tough. Supersweet varieties retain their sweetness longer than su and se varieties; extra tender varieties maintain eating quality even longer.