Skip to main content

How to grow and harvest glass gem corn

basket filled with glass gem corn on the cob
Image used with permission by copyright holder

Glass Gem corn has gotten lots of attention since it debuted on Facebook in 2012, and it’s no wonder. This unbelievably sparkly, pastel-rainbow-colored corn looks like something out of a story book. And, although it isn’t used like sweet corn, it’s not simply an ornamental novelty either. Glass Gem is a type of flint corn, which is dried and used for making popcorn, or ground into cornmeal. But don’t expect to find this beauty in the grocery store. If you want to see it in real life, you’ll probably have to grow your own.

What is Glass Gem corn?

Corn (Zea mays) is divided into five major categories: sweet corn, which has a high sugar content and is eaten green; flour corn, which is high in starch and used for cornmeal and flour; dent corn, which is used for animal feed and processed foods; pod corn, which has a husk covering each kernel and isn’t used commercially; and flint corn.

Flint corns, including the Glass Gem variety, produce very hard kernels and are known for significant color variation. They’re mostly grown either for livestock feed or for ornamental purposes, with the exception of popcorn cultivars. Popcorn is a unique subgroup of flint corn with kernels that retain enough moisture to make the kernel expand and explode when heated.

Glass Gem corn at a glance

Glass Gem corn is a warm season annual in the grass family. The plants take 100 to 110 days to grow from seed to harvest. They’re pollinated by wind and gravity when the pollen grains (produced by tassels on top of the stalk) fall onto the corn silk (which grows from the tips of the ears).  The stalks grow 6 to 10 feet tall, and produce between 2 and 5 ears per stalk. The ears measure from 3 to 8 inches long.

ears of glass gem corn
Image used with permission by copyright holder

How to grow Glass Gem

Over the past few years, more and more seed suppliers have begun offering Glass Gem seeds. You’ll find it available for order from catalogue companies and online sellers that deal in unique, rare, and heirloom cultivars, such as Native Seeds/SEARCH, Baker Creek Heirloom Seeds, Botanical Interests, and others.

Growing conditions

Choose a planting bed that gets full sun exposure, at least six hours per day. Corn requires well-drained soil with ample organic matter. Amend the bed with compost and a balanced, slow-release fertilizer at planting time. Loosen the soil to a depth of 10 inches.

For the best yields, it needs an inch of water per week from a combination of rainfall and irrigation. Corn is especially sensitive to moisture needs from the time the silks appear until the kernels fill out. Discontinue irrigation once the kernels start to harden.


Plan your corn patch for good pollination. Since wind is the chief pollinator, the physical layout can help maximize plant-to-plant pollen transfer. Rather than planting a single row, sow seeds in blocks of at least four rows.

Sow the corn seeds directly in the garden one to two weeks after your average last frost date. Plant them 1 to 1.5 inches deep in pairs, with the pairs spaced 12 inches apart within the rows. Separate the rows by 24 to 36 inches. Water well after planting.

Thinning and cultivation

Your Glass Gem seedlings will emerge five to ten days after planting. When the seedlings are 4 inches tall, thin them to one seed per 12 inches. One month after the seedlings emerge, apply granular fertilizer in the row beside the corn plants and lightly work it in with a garden hoe or cultivator. Keep the garden well weeded to eliminate competition for water and nutrients.

Pest management

Although Glass Gem corn is a relatively easy-going crop, corn earworm can be very destructive. The pest is actually the larval stage of a tan-colored moth. Look for a 1 to 2 inch, light yellow, green, pink, or brown caterpillar with white and dark linear strips along the sides. It feeds on corn silk and bores into the ears, consuming cob and kernels. The same pest feeds on tomatoes, beans, and other garden crops.

Defend your corn against earworm by making your garden a haven for predatory insects such as lacewings, ladybugs, and parasitic wasps and flies. Adjacent plantings of sweet alyssum can help. Inspect developing ears for damaged silk and boreholes near the tips. Apply two or three drops of mineral oil just inside the ear about five days after the silks appear.


Allow the ears to dry on the cornstalks. Check them by peeling back the husk and inspecting a few kernels. When the kernels are hard and you can’t make a mark on them with your fingernail, they’re ready.

To harvest the corn, twist and break the ears from the plant before the first fall frost. Cure the ears to prevent mold. Peel back the husks and hang the ears in a cool, dry, dark location for four to six weeks. To strip the dried kernels from the cob, twist the cob back and forth in your (gloved) hands.

Mark Wolfe
Former Digital Trends Contributor
Mark Wolfe is a freelance writer who specializes in garden, landscaping, and home improvement. After two decades in the…
Canna lilies add drama to any garden – here’s how to care for them
Keeping your canna lilies happy and healthy
A row of canna lily plants with orange flowers

If you’ve been on the hunt for a beautiful, tall flower to add to your garden then canna lilies might be just what you’re searching for. These lovely flowers are a welcome addition to most gardens, and they’re sure to bring practically any gardener joy. Wondering how to grow and care for these delightful and colorful flowers? This guide will answer all your questions, from planting them to warding off their most common pests and diseases. Whether you’re hoping to grow a single canna lily or an entire field of them, this is the guide for you.
Planting canna lilies

You can start planting your canna lily flowers any time after the last frost of the year, typically in mid-spring to early summer. If you want to start them earlier, canna lilies can be started indoors and transplanted into your garden after the last frost. If you choose to do this, start your canna lily plants about a month before the predicted last frost. Be sure to space them roughly 1 1/2 to 2 feet apart, so they have room to grow.

Read more
How to care for mandevilla, a perfect addition to your vertical garden
Learn what to do to add this vibrant plant to your space
A mandevilla plant with one red flower


Mandevilla, also called rocktrumpet, is a beautiful tropical plant native to South America, Central America, and even the southwestern part of North America. This gorgeous flowering vine looks stunning in containers and climbing up walls or trellises. If you have a vertical garden or are planning to start one soon, then mandevilla should absolutely be on your list of plants to consider. You’ll love seeing their vibrant flowers, which come in shades of red, pink, white, and yellow. Excited to start growing your own mandevilla plants? This guide will answer all your questions, from planting to problem-solving!
Planting mandevilla

Read more
How to care for larkspur, a toxic (but beautiful) flower
Add larkspur to your garden with these tips
Blue larkspur delphinium flowers

Larkspur, also known as delphinium, is known for its tall, brightly colored flowers. Coming in shades of pink, purple, white, yellow, and blue, larkspur is an easy-to-grow plant that looks stunning in most gardens and in containers. It’s also toxic, which can be a concern for gardeners with pets or small children. This guide to growing larkspur flowers will answer all your questions, so you can safely and successfully add this lovely flower to your home or garden.
Planting larkspur

Start planting your larkspur in early spring or in the middle of fall when the weather is mild. You don't need to plant the seeds deeply, only 1/8 to 1/4 of an inch deep. Space them roughly a foot apart. You can sow the seeds closer together, but you’ll need to thin them after they sprout so they have enough space. Larkspur can grow several feet tall, and while they won’t be nearly as wide, they will spread over time.

Read more