A staple of the vegetable garden, sweetcorn is popular for its sweet and juicy plump kernels. Learning when to plant corn is just one important step on your cultivation journey. This guide will explain not only when to plant corn but will also share care and planting tips as well as detailing how and when to harvest your crops for maximum flavor.
This is a staple of the vegetable garden.
What is Corn?
These are tender annual crops that belong to the grass family. Native to central America, this is the most widely planted crop in the United States and many parts of the world.
Depending on the variety they can grow to a height of between 4 and 12 ft. Large varieties can produce 1 to 2 harvestable ears on each stalk. Dwarf or baby types, can produce up to 3 ears per stalk.
Ears and kernels form on each side of the plant’s grass-like green stalk. These are female flowers. At the top of the stalk, flowering tassels develop. These are the male flowers.
From these pollen falls onto the silky threads that emerge from the ears. These silks are connected to unfertilized kernels. Pollen falling onto the silks pollinates the plant. The ear produces as many kernels as the number of pollinated silks. If pollination doesn’t occur, a cob forms.
Depending on the variety, kernels can be yellow, white, red, black or bicolored.
Different Varieties of Corn Plant
There are many different types of corn plant, including:
Of these sweetcorn is the most commonly grown and eaten variety. A popular snack as well as kitchen staple, you can eat sweetcorn either on or off the cob.
Juicy kernels are a popular snack.
There are three types of sweetcorn plant:
Standard is the old-fashioned type that your grandparents probably grew. Also known as ‘normal sugar’, there are many different types of standard corn plant including heirloom and open-pollinated types.
Standard varieties include:
- Golden Cross Bantam, taking 85 days to mature and produces large, yellow kernels. A prolific type it is resistant to bacterial wilt.
- Butter and Sugar is a bicolor variety producing white and yellow kernels with a good flavor. Blight and bacterial wilt resistant, Butter and Sugar matures in roughly 73 days.
- Silver Queens is a sweet, tender type that produces whiter kernels. Maturing in 88 days it is resistant to both bacterial and Stewart’s wilt.
- Jubilee is another sweet, tender type. Resistant to smog and smut its yellow kernels ripen within 83 days.
Sugar-enhanced varieties are hybrids. They have been bred to be both more sweet and more tender than standard varieties. Popular sugar-enhanced varieties include:
- Kandy Korn, a sweet, tender type with golden-yellow kernels. Maturing in 89 days, Kandy Korn grows in a range of climates and is a good freezing and canning choice.
- Breeder’s Choice is popular for its sweet, tender light yellow kernels. It matures within 73 days.
- How Sweet It Is produces sweet, crisp white kernels after 87 days. Retaining its flavor, this variety is resistant to most common corn plant diseases.
Super-sweet is another hybrid variety. The sweetest type of sweetcorn it can lack tenderness and flavor. It is also more demanding than other types of sweetcorn, requiring warm soil to grow. Super-sweet is less vigorous than other types of sweetcorn.
Common types of super-sweet include:
- Super-sweet Jubilee produces sweet, yellow kernels. A high yielding variety it matures in 85 days.
- Early Xtras Sweet is popular for its sweet and tender golden kernels. Ready for harvest in just 71 days, it is resistant to most common diseases.
- Sweetie is an exceptionally sweet, tender yellow variety. Ready for harvest in 82 days, Sweetie freezes well.
If you don’t have much space to grow your crops, or are growing the crops as part of a container garden, dwarf or baby varieties enable you to enjoy fresh kernels without taking up too much space. Reliable small types include Baby Asian. Strawberry Popcorn, Sweet Painted Mountain and Trinity.
While many people chose to grow sweetcorn, popcorn cultivars are increasingly popular. These share the same care needs and growing requirements as other types of corn plant. Some of the most reliable popcorn varieties include:
- White Cloud produces tender fluffy white, hull-less kernels with a good flavor. Taking 95 days to mature this heavy yielding type grows well in cooler climates.
- Gold Hybrid produces excellent quality popping corn. It matures in 105 days.
- Black Popcorn takes 100 days to produce deep blue or black kernels that are rich in flavor. This variety produces larger ears and kernels than standard types.
Kernels are not just yellow in color.
Where to Grow
One of the most important aspects of learning when to plant corn is identifying the right growing location.
Commonly grown as an annual plant, this crop is best planted in USDA Zones 4 to 8.
When deciding where and when to plant your crops, take into account light levels in your garden.
These crops grow best if they get at least 6 to 8 hours of sunlight every day. This means that they thrive in direct or full sun. However, these crops can also thrive in a low light spot that enjoys sunlight throughout the day.
Grow in a light, warm position.
Your soil should be loose or well-draining. A pH of 5.8 to 6.8 is ideal. A soil test kit tells you the pH level of your soil, enabling you to make any necessary amendments before planting.
If you practice crop rotation, plant corn in soil that previously held legumes or beans. These crops fix nitrogen in the soil.
In the fall, prior to planting work aged compost into the top 8 to 10 inches of soil. You can also use well-rotted manure. This enriches the soil and helps to sustain these quick growing crops. It also helps to loosen the soil, improving drainage.
You can also grow a green manure cover crop such as vetch or clover in the soil during late summer and fall before planting your corn. This fixes nitrogen, which is essential for healthy growth, in the soil.
An important part of learning when to plant corn is waiting for your garden to warm up. These crops grow best when the air temperature is between 60 and 80 ℉.
Your soil should also be warm. A temperature of at least 50 ℉ is necessary for seeds to germinate. Most types of corn grow best when the soil temperature is over 60 ℉, however standard varieties can tolerate soils of 55 ℉ and warmer.
Depending on the variety and heat it can take a corn plant 60 to 100 days to mature.
Can I Plant Corn in Pots?
Corn requires lots of room to grow. This, coupled with the fact that effective pollination requires several stalks, makes growing in containers impractical but not impossible. Choose baby or dwarf types with short stalks. Sow 5 to 6 seeds in a large, 5 gallon container.
If you are growing in pots, grow only one variety per pot. These crops readily cross-pollinate. Kernels that have been cross-pollinated are often disappointing and lacking in flavor.
When to Plant Corn
While you can buy transplants, corn is a quick growing plant that is easy to grow from seed. Growing from seed is also more affordable and enables you to choose from a wide range of varieties.
You can either direct sow your seeds into their final growing position or start the seeds undercover and transplant after germination. Starting the seeds undercover is a great choice if you experience longer winters.
Corn seeds germinate in temperatures of 50 ℉ and warmer. In good conditions germination takes 10 to 14 days. Corn seeds typically have a germination success rate of 75%. Start a few extra seeds to guard against failure.
Start seeds as the temperatures warm up.
When to Sow Seeds
Directly sow your seeds once all danger of frost has passed. The soil should be at least 60 ℉. While you can sow seeds into soil that is cooler than this, germination will be slower. To warm up the soil, cover the planting area with a sheet of Rocky Mountain Goods Black Plastic Sheeting.
Prepare the soil by munding or ridging up the earth to a height of around 3 inches. This helps to promote drainage. It also supports the stalk as it grows.
Before sowing, dusting the soil with a nitrogen-rich cottonseed or soybean meal can help to promote growth. Apply roughly 3 pounds per 100 square ft.
In spring and early summer, sow your seeds 1 inch deep. After the weather has warmed up, from mid-summer on, sow seeds 3 to 4 inches deep.
Space your seeds 2 to 3 inches apart. Rows of crops should be spaced 20 to 26 inches apart. Allowing the stalks to grow too closely together can impact on height and spread.
Following germination, allow the seedlings to reach a height of 4 to 6 inches before thinning out. Thin out the seedlings to a spacing of between 12 and 18 inches for short types or 18 and 24 for taller varieties.
Corn is pollinated by wind as pollen falls from tassels. Many people grow these crops in a 2 to 3 ft square block pattern. This helps to maximize pollination rates, meaning that you get lots of full ears of corn.
If you want a regular supply of fresh kernels throughout the season, start successive sowings every 2 to 3 weeks. This should give you a regular supply of fresh corn until well into fall.
While you can space them out, if you have the room you can grow early, midseason and late varieties at the same time.
When to Start Seeds Undercover
To get a head start on your growing season you can start seeds undercover in a greenhouse or on a kitchen windowsill.
Start your seeds just as the outside temperatures start to warm up. Seedlings are ready to be transplanted outside after a few weeks of germination. Delaying this part of the when to plant corn process for too long, while you wait for the soil and temperatures to warm up, can stunt growth or plant development.
Fill biodegradable peat pots with fresh potting soil. Biodegradable YESIACE Peat Pots are great for starting crops such as corn or cucumber that dislike having their roots disturbed. Using peat pots means that instead of having to remove the seedling from the pot to transplant, you can simply plant it still in its pot. As the plant grows, the pot breaks down, enabling the roots to spread.
To sow, make a hole in the soil around 1 inch deep. Pop the seed in the hole and cover. Water well and place in a warm spot.
While moisture is necessary for germination, do not allow the seeds to sit in soggy soil. Corn seeds are unlikely to germinate in cold, wet soil.
When to Transplant Seedlings
When considering when to plant corn, remember that this is a summer crop. Aim to transplant in late spring when the soil temperature is at least 60 ℉. This is usually achieved 2 to 3 weeks after the last spring frost. A temperature range of 60 to 95 ℉ is ideal.
To transplant, mound up the soil and make a hole in the middle of the mound large enough to hold the pot. When placed in the hole, the lip of the pot should sit level with the top of the soil. Planting so that the top of the pot is slightly above soil level can help to encourage excess moisture to drain away. After positioning, firm down the soil around the transplant and water.
While the soil is now warm enough for your seedlings, the nights can still become chilly. Protect your young transplants and seedlings by covering them with an Agfabric Floating Row Cover.
How to Care for Corn Plants
Knowing when to plant corn is just a small part in your growing journey. These quick growing crops require care and attention to ensure a flavor-filled, bountiful harvest.
These are shallow-rooted specimens. This means that weeds can easily rob them of the nutrients and moisture that they need. When the stalks are young, weed the soil regularly. This is especially important during the first month of growth when stalks are particularly fragile.
After a few weeks, when your crops are settled and established you can use a layer of mulch to deter weed growth. This also helps the soil to retain moisture. Alternatively, a ground cover crop of clover helps to fix nitrogen in the soil, sustaining growth and deterring weeds.
When to Water
Part of the grass family, these specimens require regular moisture to keep them healthy and happy. If it doesn’t rain, apply 1 to 2 inches of water a week. During periods of hot weather these crops require more water.
If you are unsure when to water, a soil moisture sensor provides a reliable way to find out how dry your soil is.
Use a soaker hose or drip irrigation system to water the base of the plant. Keep the rest of the plant, particularly the tassels as dry as possible when watering. Wetting the tassels causes water stress, impacting on pollination and reducing the amount of kernels a plant produces.
Water the soil, keeping the stalks as dry as possible.
Covering the soil around the base of the stalk with a straw mulch helps the soil to retain moisture for longer, reducing how often you need to water.
How Often Do I Need to Fertilize?
This is a heavy feeding crop. Before planting, in fall or early winter, work compost into the soil. Alternatively, work a thinner band of compost into the soil around 2 inches away from your seeds. This band of compost should also be at a deeper level than your seeds.
Apply a dose of nitrogen rich fertilizer when the stalks reach a height of 8 inches. This can be repeated when the stalks reach a height of 18 to 24 inches and again when the tassels form. If you don’t want to use fertilizer, you can side dress the growing stalks with aged compost.
If you don’t have any compost you can also side dress with one of the following products:
- Nitrogen-rich blood meal,
- Feather meal,
- Aged chicken manure,
- Alfalfa meal,
- Cottonseed meal.
The practice of growing mutually beneficial crops and flowers together, corn is a good companion plant for:
Marigolds and white geraniums are also useful companions. Both these flowers deter Japanese beetles.
Avoid planting close to berries and pole beans.
When to Hand Pollinate
This crop is pollinated by the wind. To help the process along, shake the tassels every day starting when the silks emerge from the years. This encourages the pollen to fall from the tassels onto the silks. Continue to do this for several days.
These crops are prone to cross-pollination. This can cause the kernels to lack flavor or interest. If you are growing different varieties, cross-pollination is easy to prevent. Simply plant your different varieties two weeks apart. This means that the tassels form and release their pollen at different times.
Following pollination, cover the ears with paper bags to stop birds stealing your kernels.
Poor kernel development can be poor pollination, overcrowding or potassium deficiency in your soil.
Purple stalks are a sign of a phosphorous deficiency.
Maturing stalks falling over, known as lodging, can be straightened up by packing soil around the roots and crown. Hilling stalks early in the season can prevent lodging. To lodge or hill the soil, use a hoe to draw soil up around the stalks as they mature.
As they grow, the stalks are prone to falling over.
Use a floating row cover to protect seeds and young stalks from birds, beetles and caterpillars. As the stalks develop, caterpillars and beetles can be handpicked from the stalks. Cutworms, wireworms, corn earworms, corn borers and flea beetles can also be handpicked from the plant.
Corn earworms are moth larvae. The eggs hatch on developing silks enabling the small caterpillars to crawl along the silks into the ears where they feast on the tips. To prevent this, put a few drops of vegetable oil onto the ear silks as they start to brown.
Corn leaf aphids are blue-green in color and suck sap from the foliage, stunting growth and impairing pollination. Aphids can be washed off the leaves with a blast from a garden hose. Encouraging natural predators such as lady beetles of green lacewings to your garden can help to keep aphids under control.
Japanese beetles are metallic copper in color and chew corn silks. Their larvae are white grubs around an inch long. Hand pick the beetles off the stalks. Severe infestations can be treated with Bacillus thruingiensis (Bt).
Regularly check the foliage for signs of infestation.
Smut is a fungal disease that turns kernels gray or black. It can also cause the kernels to swell up. Should smut develop, dig up and destroy affected crops. Smut spores can exist in the soil for 2 years. Don’t plant this crop in the same area until you are sure the spores are gone.
Stewart’s wilt is a bacterial disease that is spread from plant to plant by flea beetles. This disease causes leaves to yellow and stunts growth. Today there are a number of disease resistant varieties available. You can deter flea beetles by placing wood ash or agricultural lime around the stalks.
These crops are also susceptible to rust, Anthracnose, leaf blight and leaf spot. Adopting good growing practices, spacing stalks out and implementing a basic crop rotation system can help to prevent most pathogen diseases.
Slugs can also attack young stalks. Our guide to getting rid of slugs from your garden contains lots of useful, easy to implement suggestions.
Finally, traps and fences can be used to deter rodents and raccoons.
When to Harvest and How to Store
Your corn plant is ready to harvest when the ears turn a dark green color and the silks turn brown and start to wither. This is usually around 3 weeks after the silks develop.
Ripe kernels retain their peak sweetness for just 2 to 5 days.
Harvest when the silks wither.
To test whether it is time to harvest, pull back part of a husk and pierce a kernel with your thumbnail. A milk juice seeping out of the kernel means that the ear is ripe. A watery juice indicates that the ear is still immature; allow the ears to remain on the plant for another day or two. Pasty juice emerging from the kernels means that the ear is overripe.
Ears are best harvested in the morning, when the kernels are full of moisture.
To pick your corn, grab the ear and give it a sharp twist downwards. This separates it cleanly from the plant. After harvest, plunge the ear immediately into a bucket of cold water. This helps to preserve the sweetness of the ear.
Corn is best eaten fresh. If you aren’t using the ears immediately, keep the kernels in their husks until you are ready to cook. Use a sharp knife to remove the kernels from the ear.
This crop is best used fresh.
You can keep unopened husks in a refrigerator for up to 3 days. Wrap the husks in a damp paper towel before placing in the refrigerator. For slightly longer storage, the cobs can be cooked before placing in the refrigerator. This keeps them usable for up to 5 days.
For longer term storage, blanched cobs can be frozen for 3 to 6 months. Cooked cobs can be kept in a freezer for up to 12 months. However, freezing cobs can take up a lot of room.
Another option is to cut the kernels from the cob with a sharp knife. Lay the kernels out flat on a baking sheet and flash freeze. They can then be stored in a large plastic bag in the freezer.
A staple of the kitchen garden or allotment, learning when to plant corn is an important part of correctly caring for these crops. Once you have mastered this skill you will find that corn is a welcome addition to the garden.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.