Page 1 of 5 of the Sweet Corn Guide

How to Choose the Best Sweet Corn

Author: Greg Baka

As a member of the grass family, and presumed to be the oldest cultivated crop, corn is relatively easy to grow. Corn simply needs warmth, moisture, sunlight, wind protection, a long growing season and deep, well-drained soil with plenty of organic matter.

Relax. It is not as complicated as it sounds.

Sweet Corn Basics

Corn is wind-pollinated. So, short rows next to each other are apt to grow more ears than one long row. The richer the soil, the closer together the plants may be. Four rows, 3 feet apart, and 5 feet long is an ideal garden size.

Bicolor variety of sweet corn Image Credit

Corn loses its sweetness after picking, so planting more than your family can consume is impractical unless freezing or canning the excess immediately. Running directly from the garden to the table with freshly picked produce is the best practice for sweet corn.

Corn takes up a lot of space for the amount of food produced (roughly 60 ears in a 100 foot row). However, planting corn has other benefits. All those nitrogen-rich leaves, stalks, husks and cobs make excellent garden mulch. Ground corn cobs are highly resistant to compaction, so the mulch remains loose even if your garden gets plenty of foot traffic.

Pole beans can be planted with corn, as beans use the stalks for support while fixing nitrogen in the soil for the corn. A win-win partnership!

But first, one must decide which corn variety to plant.

Sweet Corn Varieties - How To Choose

Below are the five categories of sweet corn:

  • Standard (su)

    is the oldest form and most familiar. These are some of the hardiest varieties. Almost immediately after picking, the sugar in the kernels begins to change to starch, so this type should be eaten as soon as possible after plucking from the plant.
  • Sugary Extender (se)

    varieties have more sugar per kernel than the standard types, making them perfect for market growers or when the corn isn’t eaten the same day it is picked. These varieties will retain their sweetness for 2 to 4 days after harvesting. The kernels are more tender than on standard sweet corn, requiring gentle handling and harvesting by hand.
  • Supersweet (sh2)

    is also known as shrunken types. This corn has 4 to 10 times as much sugar per kernel as the sugary extender. With proper handling and refrigeration this sweet corn will retain its sweet flavor for up to 10 days after harvesting. However, these varieties require higher germination temps than the standard or sugary extender varieties. Precise planting depth is necessary for maximum germination. Plus, they must be isolated from all other corn varieties to prevent cross pollination, ruining both crops.
  • Synergistic (sy)

    varieties combine the genetic traits of standard, sugary extender and supersweet all on one ear of corn. Each kernel portrays the trait of a different type. This type yields a sweeter ear than standard, yet hardier than sugary extender varieties. Isolation from other corn varieties it is not necessary. It can tolerate some mechanical harvesting.
  • Augmented Supersweet

    also has combined traits. However, every kernel will have the traits of a supersweet corn variety. Plus, it will have some characteristics from both the standard and sugary extender varieties. It requires manual harvesting and isolation from other types.

Sweet corn is available in a wide range of sweetness. If this is your first time planting sweet corn, we recommend the standard varieties. You can add the more sugary varieties next season if you find standard is not sweet enough.

Which type of sweet corn to plant?

Best sweet corn varieties Image Credit

The types listed above contain numerous varieties, each with their own maturity dates, sweetness and size. If this is your first time planting sweet corn, check with your local extension agency, community garden coalition or gardening friends to learn which varieties have been successful for them. Consider the length of your growing season, available space and taste preference.

The University of Illinois Extension Office provides a list of recommended sweet corn varieties.

Other considerations when choosing a sweet corn variety

Height of corn

Since corn is a tall crop, consider where to plant it to avoid shading other parts of the garden. Varieties vary greatly in height. Some early season varieties only reach 4 to 5 feet in height while later season varieties typically grow more than 7 feet tall.

Length of time to maturity

Sweet corn matures in 60 to 100 days. This information will be spelled out on the seed packet or website. Garden catalogs and seed packets also provide zone charts to aid in determining the length of growing seasons.

Water availability and needs

Corn does best when the soil maintains a steady amount of moisture in the 50 to 75% range, or about 1 to 2 inches of water per week. (See our moisture table below.) Some varieties can withstand light drought conditions, although all varieties should have plenty of water when the cobs are forming. A layer of straw put on when the weather gets hot helps hold moisture for the developing corn.

  • Corn plants need approximately 1 1/2 inches of water every week in order to thrive and reach their full potential. Drought conditions will result in stunted plants with small cobs.
  • Water in the morning so the sun will dry the plants, preventing water from remaining on the ears and causing mildew.
  • One long soak once per week is better than several short watering sessions as plants take up water and nutrients through their roots.
  • Consider rainfall when watering. Too much watering may also stunt the growth of the corn plants by washing away nitrogen and compacting the soil.
  • Continue mulching throughout the season, adding more as the plants grow, to retain moisture and suppress weeds.

Common soil amendments include compost, grass clippings, straw, shredded leaves, rotted manure and dried seaweed. Other organic materials such as spent garden plants, peels, and husks, chopped corn cobs and stalks, peanut shells, coffee grounds, wood ashes, feathers, shredded newspaper (a favorite among worms), pet hair, spoiled hay, and small pieces of cotton, wool or linen fabrics can be turned under to improve clay soil.

Wood chips, bark and sawdust also loosen soil, but will zap nitrogen (needed for decomposition) from the soil if applied too heavily. Pine needles are not recommended unless lime is also added to counteract the acid conditions produced as conifers decompose.

Length of harvest

For fresh eating, plant a minimum of 10 to 15 plants per person. To extend the harvest, sow an early-maturing type every 2 weeks for 6 weeks. Or, plant early, mid-season, and late types at the same time. To avoid cross-pollination, separate different corn cultivars (especially supersweets) 400 or more yards apart or plant them so they tassel at least 2 weeks apart.

Testing Seeds

Testing corn seed for germination

Corn seed is usually viable for just one year, so should be planted the year it is purchased. The average germination rate of sweet corn is 75%. Seed can be tested for germination as outlined below.

  • Count out some seeds, (the larger the sample the better your experiment results, yet you don't want to waste seeds that you could grow).
  • Soak seeds for 4 hours to overnight.
  • Place seeds onto a paper towel or coffee filter and close with a bread tie or rubber band.
  • Wet the paper with a spray bottle until completely wet, but not dripping.
  • Place the seeds and paper inside a closed clear plastic bag, plastic container or glass jar.
  • Check on the third day and count the number of seeds that have a good root started.
  • Remove the sprouted seeds and close up the paper towel and replace in the container
  • Make sure it remains damp but not wet. If it is dry use your spray bottle and mist your seeds again.
  • Repeat every other day until no more seeds sprout, which should not be more than 7-10 days for most varieties.

More information on environmental factors that effect seed germination is available here.

With a 50% germination rate, consider placing 2 seeds in each hole spaced 10-12 inches and then thinning to the best plants. Replant the few that do not sprout at all.

Read seed packets completely

Now that you know a little bit about the different varieties, it is time to actually choose what corn you are going to plant. Take the time to read all the information on your seed packet or online prior to purchasing. That packet will provide you with information like days to maturity, days to germination, when to plant, and which growing zone that variety will grow best in. Be sure to safely store the empty packet at after planting so that you have information for choosing plants again next year.

Guide for estimating soil moisture

Checking soil moisture by hand Image Credit

If your soil is coarse to moderately coarse

  • 100% to 75% - forms a weak ball breaks easily when bounced on hand
  • 75% to 50% - will form a ball, but immediately falls apart when bounced on hand
  • 50% to 25% - soil appears dry, will not form a ball with pressure
  • 25% to 0% - dry, loose, soil flows through fingers

If your soil is of a medium texture

  • 100% to 75% - forms a ball, very pliable, easily sticks together
  • 75% to 50% - forms a ball, sticks together under a little pressure
  • 50% to 25% - can form a ball, easily crumbles with pressure
  • 25% to 0% - powdery, crumbles easily

If your soil is of a fine and very fine texture

  • 100% to 75% - easily ribbons out between thumb and forefinger
  • 75% to 50% - Forms a ball, will ribbon out between thumb and forefinger
  • 50% to 25% - Somewhat pliable, will ball under pressure
  • 25% to 0% - Hard, difficult to break into powder

walk-behind garden seeder for planting corn Hoss Garden Seeder

Now that you know which sweet corn variety to plant, in our next article we will explain how to plant those seeds for maximum yield.

Click a page below to read the rest of our Sweet Corn Guide