Sweet corn (Zea mays) is a summer staple in many parts of the world. You might see self-serve stands pop up around your town when the season arrives or an overflowing display at your local supermarket. But nothing’s quite as sweet as growing your own.
Corn is a significant crop, both culturally and economically. As a result, we know far more about the plant’s development and various growth stages than some of the other vegetables we like to raise.
Though resources designed for large-scale farmers can be overwhelming for the home gardener, they may provide unique insights into the world of growing corn!
In this article, I’ll break down the key corn growth stages to help you better understand what your sweet corn crop is up to during the summer months.
Conditions for Growing Corn
Corn is a warm-season annual, meaning it lives for just one year and doesn’t tolerate frosty temperatures. As you may already know, corn is also a member of the large grass family, which is essential to remember as you learn about its care and overall growth cycle.
You can start your corn from seed (in my experience, this is the better option) or small nursery transplants. Most varieties need 60 to 100 days to mature, so plan to get your corn plants in the ground shortly after all threats of frost have passed.
Like most of our stalwart vegetable crops, corn plants like full sun. This translates to roughly 6 to 8 hours of direct sunlight per day. Corn grown in warmer climates may require less sun and vice-versa.
Corn also needs consistent moisture to produce cobs of plump kernels. However, well-draining soil is equally as essential to maintain root health and stop the spread of certain fungal diseases.
Though not the most popular crop for a container garden, corn can definitely be grown in a small space like a patio or apartment balcony. I recommend using a container that is at least 12 inches wide and deep.
Corn Growth Rate
Corn is fast-growing with a relatively straightforward life cycle. Since corn is a grass, it does not branch out but instead grows from a single stalk.
Corn can grow up to 4 inches daily when conditions are right. This rapid growth typically happens toward the end of the growing season.
According to Penn State Extension, you can also monitor corn’s growth rate by tracking the number of leaves. Young plants may produce new leaves as often as every 3 to 4 days. Once the corn is at least knee-high, this rate can increase to every two days.
Growth Stages of Corn
Most corn grown by home gardeners (and sold at farmer’s markets and grocery stores) is sweet corn. These varieties are specifically bred to have higher sugar content, giving them a yummy and nutritious flavor profile.
The average sweet corn plant requires 60 to 90 days to go from seed to harvest.
Aside from sweet corn, there are five categories of corn you might encounter:
- Pop
- Flour
- Flint
- Waxy
- Dent
Some of these varieties are used for human food — as is the case with popcorn — while others — in particular, dent corn — are used for animal feed or even to create bio-fuel. (According to some sources, up to 40% of corn crops today are transformed into ethanol!)
When it comes to actually growing corn, these variations have little impact on the plant’s cultural needs or life stages. But they do play a role in determining the best time to harvest.
1. Seed Germination
To grow a stalk of corn, you first need a healthy seed. You likely already know (or have at least guessed) that corn seeds come from the kernels we harvest and eat. The grains are also considered a fruit, though only a skinny layer of non-seed tissue surrounds the seed coat.
Each ear of corn can contain hundreds of viable seeds. Each seed (or kernel) will produce one corn stalk if successfully germinated.
In ideal growing conditions, corn seeds usually germinate in 7 to 10 days.
According to Purdue University, corn seed germination is triggered when the seed absorbs at least 30% of its weight in water. In other words, adequate and consistent soil moisture is critical to speedy germination.
Soil temperature is also significant in determining how quickly corn seeds germinate and emerge from the soil. A difference of just 5°F — 60°F versus 55°F — can more than double the number of days it takes corn to sprout!
Once germination begins, the first physical change to occur is the emergence of the radicle or primary root. This happens after about 2 to 3 days in good conditions.
An embryonic structure called a coleoptile or ‘spike’ emerges after another day. This structure protects the embryonic leaves as they exit the seed and move up through the soil.
The final step in corn seed germination is the appearance of lateral seminal roots. These roots grow outward, anchoring the seed and accessing key moisture from the soil.
2. Seedlings
The seedling stage more or less begins as soon as the coleoptile or ‘spike’ breaks through the soil surface. This is sometimes called the VE stage. Shortly after the coleoptile appears, the corn plant’s first genuine leaf grows from the top.
Early corn growth is broken up into several visual stages:
- V1 — The first leaf has fully emerged, and the leaf collar is visible. Occurs about 3 to 4 days after seedling emergence.
- V2 — Two leaves have fully emerged. Occurs about 7 to 10 days after seedling emergence.
- V3 — Three leaves have fully emerged. Occurs about 10 to 20 days after seedling emergence.
Beneath the soil, the corn’s roots are also changing. The plant’s primary root system is not the radicle and lateral Seminole roots. These structures stop growing by the time the seedling reaches the V3 stage. At this point, permanent nodal roots take over and sustain the corn plant for the rest of its life span.
3. Vegetative Growth
While the V3 stage marks the end of the corn plant’s reliance on its embryonic root system and the energy reserves within the seed itself, there’s still plenty of growing left to do.
This vegetative growth is commonly divided into several more stages, going all of the way up to V18 or greater. The final stage typically ends 60 to 70 days after the seedling first emerges when the flower structures mature.
When the corn plant reaches stage V7, growth picks up speed considerably. The plant should be at least 2 feet tall once it comes to the V8 stage and 4 feet tall by the V12 stage. You can continue tracking the corn’s progress by counting the number of fully emerged leaves and leaf collars along the stalk.
Many people don’t know that the kernels also develop during this period of vegetative growth. While the immature seeds still need to be successfully pollinated to produce a viable harvest, the number of healthy kernels within each ear of corn is already determined by the V17 stage.
4. Flowering
Corn plants have two types of flowers: tassels (male) and silks (female). The tassels grow from the very top of the corn stalk, while silks grow from the end of each ear.
The tassels emerge approximately 65 to 75 days after seed germination, during what’s called the VT stage. About three days later, the silks will fully emerge. The VR or R1 stage is the actual start of the corn’s reproductive cycle.
Tassels are covered in pollen. Meanwhile, silks consist of individual ‘hairs’ connecting to a separate ovule (or potential kernel) inside the respective ear.
5. Pollination
The wind primarily pollinates corn. The wind blows the tassel atop the corn stalk, knocking pollen free that falls onto the silks directly below or on adjacent plants.
Corn is an example of a self-fertile plant. This means that pollen from a given stalk’s tassel can successfully pollinate silks on the same plant. Cross-pollination (pollen going from the tassel of one plant to the silk of another) accounts for up to 95% of corn crops.
You might also spot bees and other insect pollinators visiting the golden tassels when they are covered in pollen. While these insects don’t directly transfer pollen from the tassel to the silks, they do often knock free pollen just as the wind does.
6. Fruit Development and Ripening
It shouldn’t be surprising that kernel development is also broken up into several distinct stages. You can estimate which stage your corn ears are in by counting the days since silking or when the silks first appeared.
The blister stage (R2) is marked by the silks drying out and visibly turning brown. Inside the ear, fertilized kernels begin to form individual embryos. This usually happens about 12 days after silking.
During the milk stage (R3), kernels turn bright yellow and contain lots of sugar. This is the time sweet corn should be harvested for the best flavour. The milk stage occurs an average of 20 days after silking.
There are three more possible stages of kernel development: dough (R4), dent (R5), and black layer (R6). It takes about 60 days from silking for an ear of corn to go through all stages.
Corn left to complete all stages is used for things like animal feed or ethanol production. In other words, this info isn’t very relevant to home gardeners.
When to Harvest Sweet Corn
As I briefly explained in the previous section, sweet corn is typically ready to harvest 20 days (or three weeks) after silk development. Remember that ripening begins with ears at the top of the stalk and works its way down to the bottom-most ears.
Sweet corn is best picked during the milk stage, which hints at how to check the kernels’ ripeness. Just puncture a kernel with your fingernail and check for a milky liquid.
The ideal harvest period for sweet corn can be very fleeting, especially in hot weather. I recommend checking for ripe ears every day at the least, or else you may miss the perfect moment to pluck your corn from its stalk!
For more insight into the growing cycles of vegetative plants, here’s a link to Cabbage Growth Stages.
FAQ Corn Growth Stages
Should corn be knee-high by July 4th?
US citizens have probably heard that corn fields should be knee-high by July 4th or Independence Day. This adage is outdated due to advances in corn genetics and growing practices, so modern farmers believe corn should be much taller than knee height by July!
Citations
- Penn State Extension How to track corn growth rate via leaves
- Purdue University Corn germination requirements
- Bayer Crop Science Corn self-pollination rate
- Kruger Seeds Kernel ripening stages
Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.
