When to plant corn depends on how soon the weather warms up. The typical time for planting corn is 2-3 weeks after the last frost but the best indicator is when soil temperatures are averaging above 60 degrees Fahrenheit. The most likely culprits of having to replant are a late frost or heavy rainfall.
Corn grows best with air temperatures from 60-90 degrees Fahrenheit. The variety of corn you’re growing will tell you the latest date you can plant the corn. The colorful variety of corn pictured above is called Earth Tones.
Plant late enough small corn plants won’t get hit with a spring frost but early enough the variety you’re growing has enough time to reach maturity before cool temperatures hit in the fall.
Commonly grow corn varieties fall into early, mid, and late season categories that reach maturity in anywhere from 60-120 days. By planting an early, mid, and late variety you’ll have corn throughout the summer. If you’ve got a variety you really like you can successively plant that every 2-3 weeks and have corn all summer that way.
Soil Temperature For Planting Corn
By planting when the soil temperature is right it gives seed corn the best chance of sprouting. The soil temperature should average above 60 degrees. To get a good average soil temperature measure between 9-11 AM when the night time chill has worn off and before the afternoon sun inflates the temperature.
You can use a meat thermometer if the gauge reads low enough or buy a soil temperature gauge that looks just like a meat thermometer but reads down to zero degrees. Place the thermometer in the soil and leave it for five minutes. If it reads above 60 and you don’t expect any more frosts it’s a good time to plant.
When Do Farmers Plant Corn?
Farmers plant corn the same time as gardeners, when the weather allows for it! Gardeners can actually get a head start on farmers by using row covers that warm up the soil temperatures or starting corn indoors. Neither of these methods is feasible for farmers.
If farmers plant before a certain date it can negate their crop insurance coverage for replanting. Factor in labor, fuel, and seed costs and you can bet most farmers will not violate the replant provision in their crop insurance policy and will wait until whatever date the insurance company figures for their state or area.
However, if farmers plant too late they will not get a good yield.
On June 12, 2013 Illinois had a bad weather spring and an article out of the state contemplated the pros and cons of planting corn late. They said it was a must to have a short maturing variety and that data from the state showed that a corn field planted from June 15-20 would yield farmers about half of what they normally got from their corn fields.
The article went on to say that central and southern Illinois might do better but they also might have a tough time finding seed corn of a short maturing variety and that other factors like increased water rate loss and lower water holding properties of the soil in these areas could negate the temperature gain and later frost date.
The summary was that planting a crop this late had little room for error and would depend largely on the weather as to whether they got a decent harvest or not. One of the people interviewed said the latest he would plant corn would be June 20th. If the crop did not produce corn it could be sold as silage, a type of fodder made from green foliage that can be fed to cattle and sheep and other ruminants.
Minnesota farmers will have maximum yields by planting in late April to mid May. If Minnesota farmers are forced to plant after mid May they will choose faster maturing varieties but will still have lower than maximum yields that year.
In northeast Iowa farmers aim for April 12 to April 30, central and northwest Iowa from April 15 to May 9, and April 17 to May 8 in southern Iowa to achieve maximum yields.
Germinating Corn Seeds
Seed corns should germinate if soil temperatures are above 60 degrees. They will germinate faster with warmer temperatures and slower with colder temperatures. They can sprout in as little as 4 days or take as long as 3 weeks.
If soil temperatures are below 60 degrees the seeds will take up water and swell but won’t germinate because it’s too cold. The swelling and not germinating invites rot.
Generally the longer the seeds are in the soil without sprouting the higher chance for seed rot or a heavy rain period that can cause poor germination rates.
The best way to germinate corn is to put the seed kernels in the ground when soil temperatures are right and to water the seeds if there is no rain. Moisture is necessary for germination. It activates catalysts within the seed that cause the germination process.
If you have corn seeds that you’re not sure if they’re good or not and want to test germination rates without planting them you can.
Take a couple of paper towels and wet them with warm water. Then wring them out so they’re moist, fold them around the corn seeds and place them in a plastic bag in an area that’s 75-90 degrees.
If the area is on the warmer side keep an eye on the paper towels and rewet them if they dry out. The seeds should sprout in 2-4 days. Here’s an article that goes more in depth on germinating corn seeds.
Starting Corn Indoors
Starting corn indoors can give you a longer growing season and give corn plants a healthy start. Sometimes trying to get corn planted early outside is futile and can lead to wasted corn seed and frustration as you stare at dirt and see nothing green coming out of it.
Corn has roots that are sensitive to transplanting so it’s better to start corn plants in compostable starter pots that you can transplant straight into the ground as opposed to starting them in potting soil. No stress at any stage throughout the growing cycle leads to the best growth possible.
You can use cardboard egg cartons by poking toothpick size holes in each egg space and cutting the individual egg spaces apart when planting. Sometimes you have to pull the cardboard apart a little if it hasn’t disintegrated enough.
Best Way to Plant Corn
The best way to plant corn is every 2-3 inches in mounded rows with rows about 2 feet apart. Once plants reach 4 inches then them out to every 6 inches apart. Make mounded rows by hilling up dirt in a straight line about 8 inches tall. The mounded row will give better drainage and increased soil temperatures.
Plant corn in a block pattern with at least four short rows and avoid planting one or two long rows. Planting with more short rows in a block pattern leads to better pollination.
Spotty pollination will cause no cobs or cobs with patches of kernels missing. If you’re growing a small amount of corn plants hand pollination should be done.
Best Time To Plant Corn
The best time to plant corn is with soil temperatures averaging above 60 degrees and fairly dry conditions. If there’s 4 or 5 days in a row of rain it’d be best to wait until after the wet spell. Air temperatures between 60-90 degrees and no chance of frost either right after planting or before the plant reaches full maturity makes ideal conditions.
Please comment below if you have any thoughts or experiences on when to plant corn.