Home Garden Sweet Corn
Fresh, high quality sweet corn is one of the most popular vegetables grown in
home
gardens and purchased by consumers at roadside stands and farmers' markets. At
optimum market maturity, sweet corn will contain 5 to 6 percent sugar, 10 to 11
percent starch, 3 percent water-soluble polysaccharides, and 70 percent water.
Sweet corn also will contain moderate levels of protein, vitamin A (yellow
varieties), and potassium.
Types of Sweet Corn
Sweet corn probably originated from a mutation of an ancient Peruvian corn
called 'Chuspillo' or 'Chullpi'. Sugary forms of corn were, however, probably
not very popular in early cultures because they were difficult to store.
The first historical reference to sweet corn was in 1779 with the
introduction of 'Papoon' or 'Susquehanna', an eight-rowed, red-cob strain grown
by the Iroquois. By the early 1900s there were over 63 known cultivars of sweet
corn including 'Golden Bantam' (released in 1902), which became one of the most
popular open-pollinated varieties.
Most open-pollinated sweet corn varieties have been replaced by improved
hybrid varieties that are easy to grow, produce good yields, taste sweeter, and
store longer. Varieties are generally classified by seed color, maturity date,
or nature of sweetness.
Sweet corn varieties are available in yellow, white, or bi-colored types with
varying maturity dates from early to mid- and late season. Maturity dates will
vary from year to year and by location depending on weather (primarily
temperature). Although mid- and late-season varieties generally produce ears of
higher quality, early varieties often produce marketable ears early in the
season when sweet corn prices are at a premium.
Based on the nature of kernel sweetness, sweet corns also can be classified
into four basic groups: standard, super sweet, sugary enhanced, and synergistic.
Sweetness is not only determined by genetics, but also by how these varieties
are managed and harvested.
Field corn contains approximately 4 percent sucrose (sugar) in the immature
milky stage, while "standard" sweet corns at the same stage may contain as much
as 6 percent sucrose. (Standard sweet corns contain the recessive "su-1" gene;
field corn is dominant for the same gene, making it starchy.) Following harvest,
or if left on the stalk too long, sucrose in standard sweet corn is rapidly
converted to starch. Standard sweet corns pollinated by either field corn or
popcorn will become tough and starchy.
"Super sweet" corns contain the shrunken "sh-2" gene, which causes sucrose
levels two to three times higher at harvest than standard sweet corns. Sucrose
in super sweet varieties will remain relatively high after harvest, making them
excellent shipping varieties.
Super sweet corns have some notable disadvantages. The smaller, shrunken seed
of super sweet varieties is more brittle than standard sweet corn seed, making
super sweet seeds more difficult to handle during planting and more apt to
crack. This seed also must be planted in warmer soils (above 55 degrees F) and
at shallower depths than standard sweet corns for good stand establishment.
Although they contain more sucrose than standard sweet corn, fresh super sweet
corn kernels have tougher pericarps (crispy texture) and less water-soluble
polysaccharides (complex sugars), which give standard sweet corns their creamy
textures. Super sweet corn also must be isolated from other varieties of sweet
corn, because cross pollination with standard sweet corn will make kernels tough
and starchy in both types.
"Sugar-enhanced" sweet corn ('Everlasting Heritage'-types) has a sugar
enhancer gene, "se," which when combined with the "su-1" gene, produces
varieties with greater sweetness than standard sweet corn (between standard and
super sweet) with the same creamy texture as standard sweet corn. The "se" gene
also tends to slow the conversion of sugar to starch. Isolating sugar-enhanced
from standard sweet corn varieties is not necessary for pollination.
Sugar-enhanced sweet corns are very popular at roadside stands and farmers'
markets.
Synergistic sweet corns are not as well-known as other types. The cobs will
generally have 1/4 supersweet kernels and 3/4 standard kernels. Emergence
characteristics are similar to those of standard sweet corns.
Sweet corn varieties
______________________________________________________________________________________
Standard (su-1) Color Days to maturity
Silver Queen White 92
Golden Queen Yellow 92
Iochief Yellow 89
Jubilee Yellow 85
Golden Cross Bantam Yellow 85
Bonanza Yellow 84
NK-199 "Elephant Ear" Yellow 82
Merit Yellow 75
Early Sunglow Yellow 63
Sugar enhanced (se) Color Days to maturity
Tendertreat EH Yellow 95
Kandy Korn EH Yellow 89
Double Delight Bicolor 87
White Lightning White 86
Miracle Yellow 82
Bodacious Yellow 75
Platinum Lady White 70
Super Sweet (sh-2) Color Days to maturity
Florida Staysweet Yellow 89
Supersweet Brand 8701 White 87
How Sweet It Is White 85
Illini Xtra Sweet Yellow 85
Supersweet Brand 8202 Bicolor 82
Jubilee Supersweet Yellow 82
Supersweet Brand 7210 Yellow 78
Honey 'N Pearl Bicolor 78
Butter Fruit Yellow 72
Early Xtra Sweet Yellow 71
Sweetie Yellow 70
Synergistic Color Days to maturity
Sugarloaf White 83
__________________________________________________________________________________
Climate
Sweet corn is a warm-weather crop requiring at least eight hours of direct
sunlight daily. Seed can be planted at or after the average date for the last
killing frost. Soil temperature (in the upper 3") should be at least 50-55
degrees F or higher. Super sweet varieties require a minimum soil temperature of
60-65 degrees F. The optimum soil temperature for all sweet corns is 75-95
degrees F. Low soil temperatures at planting can cause poor germination and
retarded growth.
Successful early plantings can best be achieved by planting on sandy soils
that warm early in the spring. Seed also should be planted on the south side of
raised beds that run east to west. Covering beds with black plastic two weeks
before planting will also help warm the soil. Seed can be planted directly
through the plastic. Black plastic will also help control annual weeds.
Optimum plant growth occurs between 75 and 86 degrees F. When making
successive plantings of a single variety during the spring, later plantings will
develop faster than early plantings due to warmer, late-season weather. Thus,
the number of days between harvests will be much shorter than the number of days
between plantings. When planting early, it is best to use early varieties, as
they tend to germinate better in cooler soils.
In southern New Mexico, extremely high late summer temperatures can cause
poor pollination, especially if accompanied by drying winds. Some varieties
tolerate the heat better than others and should be considered in these areas.
Soil Preparation and Fertilization
Sweet corn will grow well on almost any well-drained soil, although deep,
sandy loams with adequate organic matter are best. Loams and clay loams are
ideal for late-maturing varieties, which require more water and nutrients. Sweet
corn will perform well at a soil pH of 6.5-8.0.
Livestock manures used in sweet corn fertilization programs should be applied
in the fall at a rate of 10-20 t/ac (apply a lighter rate for chicken manure).
Green manure crops (winter wheat, rye, and oats) planted in the fall should be
disked under at least one month before planting sweet corn in the spring. Soil
preparation should result in level seedbeds free of clods and trash. Home
gardeners may wish to incorporate 1- 3" of compost with a rototiller or garden
fork to help improve soil structure.
All phosphorous fertilizer should be soil-incorporated (broadcast) with a
disk or rototiller to a depth of 3-4" before planting at a rate of 50-80 lb/ac
of P2O5 (1-2 lb/1000 sq ft). Phosphorous also can be banded below (1") and to
the side (2-3") of the seed.
Apply nitrogen fertilizer in split applications, incorporating half (40Ð50
lb/ac or 1.0 lb/1000 sq ft) with the phosphorous before planting. The rest can
be applied in increments of 25Ð30 lb/ac of nitrogen (0.5-1.0 lb/1000 sq ft) in
bands 1" deep and 4-5" to the side of plants when they are 8-10" high and again
at 18-24" in height. Nitrogen fertilizers should be covered with soil to reduce
the loss of nitrogen into the air as ammonia.
The above fertilizer rates are dependent on the results of a soil analysis.
As most New Mexico soils have sufficient potassium, additional potassium
fertilizer may not be needed.
Planting and Pollination
Sweet corn should be planted in blocks at least three to four rows wide for
good pollination. In the home garden, a block of corn should have at least nine
plants. Some gardeners prefer to plant sweet corn in hills (two to three
plants/hill) 3 ft apart.
Early sweet corn plantings tend to be less uniform in plant growth, and ear
quality may be lower due to incomplete pollination. To prevent cross-pollination
by unwanted varieties (field corn with sweet corn, standard sweet corn with
super sweet corn, and yellow with white sweet corn), varieties should be
separated by at least 250 ft or more. Cross-pollination also can be prevented by
planting varieties with different maturity ratings (early, mid- and late season)
at the same time or by planting varieties with the same maturity rating in
successive plantings 14 days apart.
Planting depth varies for the soil and type of sweet corn. Standard,
sugar-enhanced, and synergistic types should be planted 1" deep in clay, 1-1/2"
deep in sandy loam, and 2" deep in sandy soils. Super sweet types should be
planted half as deep for each soil type.
Seeding rates will vary between 10-12 lb/ac (1/4 lb/1000 sq ft) depending on
the seed's size and the variety's maturity rating. Less will be needed for super
sweet corns due to smaller, shriveled seed. More seed may be needed for early
varieties planted closer together.
Plant spacing within the row will vary depending on row width. Plant spacing
on rows 36-38" apart may range as follows: early, 8-10"; mid- to late, 9-12".
In-row spacing between plants may increase if rows are narrower or decrease with
wider rows. Growers may find that planting "sized" seed permits more specific
and precise planting.
Some varieties may respond to wider spacing by producing more tillers or
suckers (extra stalks from the base of a plant). Removing tillers generally does
not increase yields and may actually hurt production.
When planting sweet corn, purchase only fresh seed. Sweet corn seed is
relatively short-lived (two years) even under ideal conditions. Do not save seed
from hybrid varieties grown the year before.
Although sweet corn will tolerate some water stress when young, an adequate
water supply is critical during silking, pollination, and ear development.
Water-stress at this time can cause poor quality ears. Irrigation every five to
seven days may be necessary until harvest.
Pest Control
Weeds can be controlled using shallow cultivation until the plants are 18-25"
high (for equipment clearance). For home gardeners, cultivation with a hoe can
continue throughout the season, but the need for cultivation will diminish as
corn plants mature and shade the soil beneath them. Cultivation should be
shallow to prevent damage to corn roots. Growers opting to use herbicides to
control weeds should contact their county agent or agricultural chemical dealer
for appropriate recommendations.
Major insect pests on sweet corn include
soil insects (cutworms, wireworms),
foliar insects (armyworms, flea beetles, corn earworms, aphids), and
stem borers (corn borers). Follow label instructions of registered insecticides
for appropriate control.
Corn earworms are generally the most destructive of the insect pests. Damage
is generally more severe in warmer areas of the state. Early-planted sweet corn
usually has less corn earworm damage than later plantings.
Seed rots and seedling diseases are best controlled with high quality treated
seed planted in warm soil. Field sanitation will help control over-wintering
organisms that cause various stalk rots and leaf spots.
Smut can be brought on by drought, high nitrogen levels, and plant damage
from insects, cultivation, or hail. Tolerant varieties will provide some
control.
Harvesting, Storing,
and Marketing Sweet Corn
Sweet corn ears are generally ready for harvest approximately three weeks
after silk emergence (depending on temperature). Silk will start to turn brown
about two weeks after emergence. Ears should be harvested when the kernels
appear to be milky when punctured with a thumbnail (milk stage). The unhusked
ear should feel firm (the ear will be blunt at the end), have full kernels to
the top of the ear, and have brown, dry silk. Fully ripe kernels of sh-2
varieties will still possess a clear, watery juice.
Ears of standard varieties will remain in prime condition for only a short
time in warm weather when compared to cool weather. Harvest in the early morning
when both the ears and weather are cool. High temperatures will quickly lower
the eating quality of sweet corn.
When harvesting, break the shank (or stem) of the ear as close to the ear as
possible without breaking the main stalk. Long shanks and flag leaves should be
clipped to reduce moisture loss. Ideally, ears should be cooled to 32 degrees F
within an hour of harvest.
If corn cannot be refrigerated immediately, it should be stored in the shade
to reduce heating from the sun. Do not store ears in large piles, as heat from
respiration will raise the temperature of the corn. When harvesting for direct
market sales, harvest only a one-day supply and keep as cool as possible.
Field heat can be removed from ears by passing them through a 40 degrees F
water bath (hydrocooler). Ears can then be packed in wirebound crates, topped
with ice, and held at 32 degrees F (90 percent relative humidity). Ears will
remain marketable for five to eight days. Super sweet varieties can maintain
good quality for 10-12 days.
02/01/2009
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