Page 2 of 5 of the Sweet Corn Guide
Growing Sweet Corn
Author: Greg Baka
There is no substitute for home-grown sweet corn. Corn’s sugar content, and with it the flavor, is lost very rapidly after the ears are picked. That is why it is important to get the freshest corn available.
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Soil moisture(add link to take to moisture section) and temperature(add link to take to temp part), along with planting depth, are vital for corn seed germination. All three should be checked before dropping the first seeds into the ground. The correct planting depth for the variety will be printed on the seed packet. To test the other two requirements, you need look no further than right under your feet.
When to Plant Corn?
Corn is a warm-weather plant; soil temperature and high temps are even more important than daylight hours or date on calendar to determine planting dates.
Each variety has a minimum soil temperature (should be provided on your seed instructions). The optimal soil temperature for corn is 95 degrees, but we know we can’t wait for our soil to get that hot before planting. In many locations, it will not get that hot ever. For best germination, the soil should be 60 to 65 degrees at 2 to 4 inch depth.
Many corn varieties will sprout at temperatures in the 50's. However, it may take longer for your corn to both sprout and mature since growth is based on warm temperatures, explained below, and not the physical days. In cold, wet ground, the seeds may rot. Sprouts should emerge in a week to 10 days.
Taking Your Soil’s Temperature
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Soil thermometers are available commercially from about $6 and up. Some inexpensive thermometer styles can be found at HarrisSeeds.com.
A digital meat thermometer that takes the full range of temperatures or any thermometer that reads from 32° F will also work in the garden. Use a screwdriver or wooden dowel to make a hole to the proper depth to keep from breaking the thermometer.
Soil temperatures can change significantly from day to day with large fluctuations of spring temperatures. So it is important to take soil temperature readings for at least 3-5 days prior to planting and checking the next 3-5 day forecast. You do not want a big drop in temperatures just as your seeds are put in the ground.
More info on soil temp and seed emergence can be found here at Pioneer.com
Soil Temperature Why It's Important
Corn seed will rot in cold, wet soil and should not be planted until the soil is at least 50°F. Once planted, corn seeds need a two-day (48-hour) window when the soil temperature at planting depth does not drop much below 50°F, affecting germination and subsequent seedling growth.
Also, you should be sure that temperatures will stay warm enough in an 8- to 10-day window to ensure germination. A reliable 10-day weather forecast should help you determine the chances for rain and your planting depth.
Ways to Help Warm Soil
Steel Broadfork
- Good drainage - Minnesota research shows that ground with good drainage can be up to 4°F warmer than soil with inadequate or no drainage. See our Drainage Guide by navigating to the Articles section.
- Multiple shallow cultivation – hoeing only the top 1 or 2 inches with something like a Grape Hoe will help warm soil in the spring by allowing the sun's warmth to radiate deeper. Hoeing also helps with evaporation and keeping the soil from forming a hard crust.
- Deep aeration - using a Broadfork helps warm the soil as it allows passages for the colder buried air to seep up into the warm air.
- Full sun – trim trees and bushes to allow your corn area to receive full sun as early in the spring as possible. (Apps are available to help determine exact shading patterns for various times of the year at your geographic location.) But the easiest thing to do is to walk around your garden space at different times of the day and year and then remove anything shading the corn-growing area of your garden. (Of course, choosing to trim or cut trees and bushes should be considered against other benefits like shade for your house and yard or fruit, nuts and berries for eating.)
- Remove mulch – leaves and other organic matter act like insulation that keeps soil cool for longer in the spring. It also shades the ground from direct sunlight.
- Black plastic – covering your corn area with black plastic works as a solar heater to raise soil temperatures faster.
- Cloches – although corn is a tender plant, cloches can be placed over newly planted seed to retain heat like a mini greenhouse. Cloches historically are glass lids, but can be made with plastic milk jugs or soda bottles. Clear plastic troughs are also available commercially. Although this is impractical for large areas, it could help a home gardener who wants to get a jump on the corn planting season. Cloches must be removed during sunny/warm parts of the day and when the corn gets too tall.
Soil Moisture
If soil from the top 3-4 inches of your planting site breaks apart between your fingers instead of forming a ribbon or ball, moisture conditions are usually suitable for planting. The soil will crumble like sand through your fingers if it is too dry.
Click to see the easy soil moisture test on the previous page of this Guide.
To germinate, corn seeds must absorb up to 30% of their own weight in water they obtain from the soil. Ideal planting depths depend on soil type and moisture. Most often, corn should be planted 1.75 to 2 inches deep. (link to moisture chart in corn variety article)
Also consider the water-holding capacity of your soil. Plant seeds slightly deeper in sand and shallower in clay.
Since seeds start absorbing moisture in the first 24 to 48 hours after planting, tailor your seed depth to the conditions on planting day. While planting, be sure to create good seed-to-soil contact because that is what allows optimal moisture transfer to your seeds.
To speed germination, seeds can be soaked 8 to 24 hours before planting, or even sprouted in damp paper towels (sprouts generally appear in 7 to 10 days). If using sprouts, plant carefully to avoid breaking off the fragile root.
How Many Ears of Corn Per Stalk
Each stalk usually produces 1-2 ears of corn. Remember, corn loses its sweetness immediately after picking (or shortly thereafter, depending on variety), so you do not want to plant more than your household can consume quickly or store by canning or freezing.
The season can be extended by first planting an early variety, followed a couple of weeks later by a later-maturing variety.
To check the viability of your seed before planting, see more information here(link to seed testing in variety article).
Seed Spacing
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Corn is pollinated mainly by wind, so does best when planted in blocks rather than long rows. If space only allows one or two long rows, the plants can be hand pollinated for three days after the silks appear. More information can be found here on hand pollination. NOTE: This will be in a subsequent article.
We always plant a large plot of corn since we freeze much of it to eat later. We plant 2 seeds every footstep. Any seeds that do not sprout I simply go in and replant those spaces. In spaces that sprout two plants, I trim the smaller one off at ground level when the larger one is about 4 inches tall.
Another option is to plant one seed every 4-6 inches, and later thinning the sprouts to one plant every 8-12 inches.
Row Spacing
Leave enough room between rows to water, hand pollinate if necessary, weed, hill and pick the crop. This decision has a lot to do on the space that you have available. If you have unlimited space, plant your rows 36-40 inches apart. To maximize yield for a small space, rows can be squeezed to 30 with the minimum space needed to maintain the plants.
Corn can also be planted in small colonies, rather than rows. No hand pollination is required, although hand weeding is necessary with a small hoe such as our Detail Weeder when the plants are young.
Colony Planting
Create 1-foot-diameter planting circles every 18 to 24 inches. It is best to have a minimum of 4 of these planting circles in a square pattern rather than in rows. Place 8 to 10 seeds evenly spaced in this circle. Unlike rows, you allow all the plants to mature; no thinning or hand-pollination required. However, more watering may be necessary as the plants are competing more for moisture. Each colony may require fertilization to be sure the plants have the nutrients needed for successful growth. (see fertilization)
Hand Planting Tools
Dig holes or shallow trench to proper depth. There are many ways to do this and depends on the size of the plot for planting and the number of corn plants desired. The following list details tools from smallest to largest:
- Dibbler - A small hand that tool that is pressed into the soil to form a cone-shaped planting hole. Simply wrap tape around the dibbler at the depth you want to plant the seeds. Insert the dibbler into the ground to the tape to create a space for the seeds. Drop in 1-3 seeds into the hole and then press the soil down firmly on top of the seeds.
- Pointed Hoe or other Garden Hoe - For a medium-sized plot, plant seeds by making shallow furrows 1.5" to 2" deep in rows. Controlling the depth is less accurate, but so long as seeds are no deeper than 2.5 inches or more shallow than 1.5 inches, most seeds should germinate, although at different rates. But this may be a bonus because your crop will be ready to eat spaced a few days apart. After dropping in seeds, pull the soil back over the furrow and step on it to tamp it down.
- Wheel Hoe - For larger gardens, you may want to use a cultivator tooth or single plow on a wheel hoe to open your furrow. When using the plow, be careful to not open the furrow too deep. You may need to raise the handles so that the plow or cultivator does not dig as deep as normal. Make a couple practice passes down the rows until you get the feel of where to hold the handles for proper depth. After planting, close the furrow with either your feet or garden hoe and tamp the soil.
Mechanical Planters
Seed Planter and Fertilizer Side-dresser
Planting with equipment has some significant benefits over hand planting, which includes saving time, uniformity in planting depth, accurate seed spacing, and physical ease.
- Jab Planter – This tool quickly plant seeds with no need make a furrow or individual holes. The soil must be cultivated and not hard/crusted on the top so the tool is easily pressed into the soil to the proper depth. One or more seeds are placed as the jab planter is rising up from the hole. Some jab planters also automatically side dress (adding fertilizer) the seed at the proper distance. To see different types of Jab Planters, see our Seed Planter Buying Guide.
- Garden Seeders or Push Planters – These tools precisely set the depth and spacing for seeds. In prepared soil, simply walk behind the seeder; the machine will do it all for you. Also see our Push Seeder Buying Guide.
Now that you know how to plant your corn seeds, in our next article we will tell what companions plants to include to add nutrients and repel pests.
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