When glass gem corn is planted too late, in single rows, or mixed with other corn, the result is ruined ears, useless seed, and weeks of work for little reward. Planting after your last frost when soil is 60°F, in a tight block, with open pollinated seed and careful drying, gives you the colorful, jewel like ears glass gem corn is known for.
Decide if glass gem corn belongs in your garden
Pick a purpose, ornamental, eating as sweet corn, or saving seed for next year
Decide what you want before you plant. Glass gem corn is mainly a decorative flint corn. It is beautiful dried and made into popcorn or cornmeal. It is not the same as sweet corn for fresh eating.
- Ornamental, dried ears for decoration, wreaths, or gifts, plant for full color and good dry-down.
- Eating, you can pick at the milky stage for a starchy, not-sweet bite, 18 to 24 days after silks appear, but most growers plant it for drying.
- Saving seed, grow it isolated from other corn varieties and keep records of planting dates and neighbors to maintain color fidelity.
If you want both fresh sweet corn and pretty ears, plant separate blocks at least 250 feet apart, or stagger plantings and hand pollinate. For more on beginner layout and raised beds see my guide on raised bed gardening for beginners.
Prepare soil and order true glass gem seed
Test and adjust soil pH to 6.0 to 6.8, add 1 to 2 inches compost per 10 square feet, and buy certified open pollinated glass gem seed or reputable heirloom suppliers
Start with a soil test. Aim for pH 6.0 to 6.8. Raise pH with lime or lower it with sulfur according to test results. I use a local extension lab for accurate results.
Add 1 to 2 inches of compost spread evenly over every 10 square feet and work it into the top 4 to 6 inches. That is about 3 to 6 gallons of compost per 10 square feet.
Order certified open pollinated glass gem corn seed from a reputable heirloom supplier. Do not use seed labeled hybrid or ambiguous mixes if you want true glass gem color. Certified seed and clear labeling matter if you plan to save seed.
Plant glass gem corn step by step, timed to your frost dates
Plant in blocks not single rows, plant after last frost when soil is 60°F at 2 inch depth, and stagger plantings if you want extended harvest
- Check your last frost date, then check soil temperature at 2 inch depth with a thermometer. Wait until the soil is at least 60°F. In central Ohio that is usually after last frost in spring. In colder zones plant 1 to 2 weeks later. In warmer zones you can plant as soon as soil hits 60°F and frost risk is past.
- Sow seed 1 to 1.5 inches deep, 8 to 10 inches apart in rows spaced 30 to 36 inches apart. Better yet, plant in blocks of at least four short rows so pollen has nearby ears to fertilize.
- For staggered harvest, plant every 10 to 14 days for three plantings. Expect later plantings to face heat or fall frost issues in colder zones, so shorten the window accordingly.
- Label rows with variety and planting date. If you plan to save seed, leave at least 250 feet of distance from other corn varieties, or use isolation techniques described below.
I learned the hard way that single long rows make poor pollination. If you want neat borders or container experiments see my note below and the guide on how to grow tomatoes in containers for container tips.
Water and feed glass gem corn through midsummer heat
Deep water schedule, apply 1 inch per week in absence of rain, lay 2 to 3 inch mulch, side dress with 0.5 pound 10-10-10 per 25 feet of row at knee height
Water deeply. Apply 1 inch of water per week when there is no rain. During tassel and silk development increase to 1.25 to 1.5 inches per week if temperatures climb above 85°F. Measure 1 inch with a gauge or a can, which holds about 0.5 gallons per square foot.
Lay 2 to 3 inches of organic mulch between rows to conserve moisture and keep roots cooler. Keep mulch 3 inches away from plant stems.
When plants reach knee height, which is about 12 to 18 inches, side dress with 0.5 pound of 10-10-10 fertilizer per 25 feet of row. Scatter the fertilizer in a band 4 to 6 inches from the plants and lightly work into the soil. Water in immediately.
For timing and watering details, see my short guide on when to water vegetable plants in summer.
Protect ears and pollen, patrol for common pests and problems
Check silks daily, hand pollinate if tassels and silks are out of sync, watch for corn earworm and armyworms, inspect for leaf blight and smut
- Check silks every morning once tassels appear. Silks that are brown and dry within 18 to 24 days mean pollination is done for that ear.
- If tassels and silks come out at different times because of heat or staggered planting, hand pollinate. At midday when pollen is dry and abundant, shake tassels over a paper bag to collect pollen, then dust the pollen onto fresh silks with a small brush. Repeat for 2 to 3 days for full coverage.
- Scout for corn earworm and armyworms. Look under leaves and at silk tips. Pick larvae off by hand and destroy them. If you need a product, consult your county extension for recommendations and labeled controls.
- Inspect leaves for blight and smut. Remove and burn infected plant debris, do not compost diseased ears. Good air flow and not crowding the block reduces disease.
- Birds and squirrels like ears. Use row cover or netting if you lose ears to wildlife. Put covers on before silks appear, then remove for hand pollination if you are saving seed.
Harvest, dry, and store glass gem corn, and save seed correctly
For eating pick at milky stage at 18 to 24 days after silk, for drying pick when kernels dent and moisture is 13 to 15 percent, dry ears 4 to 8 weeks then store in paper sacks
For fresh eating, pick at the milky stage, 18 to 24 days after the first silk strand turns brown. Pull back a small section of the husk and press a kernel with your fingernail. If it releases milky juice the ear is ready.
For drying and seed, let ears mature on the plant until husks are brown and dry. Harvest before a hard fall frost. Desired kernel moisture for storage is 13 to 15 percent. If you do not have a moisture meter, dry ears for 4 to 8 weeks in a dry, ventilated place around 60 to 70°F, then shell and test a few kernels by biting. They should be hard, not milky.
Store dried ears or shelled seed in paper sacks, labeled with variety and harvest date. Keep them in a cool, dry spot, 40 to 50°F if possible. For seed saving make sure isolation was observed and record neighbors and distances.
Record the numbers that matter for glass gem corn
Quick reference table of spacing, depth, days to maturity, row length per person, and isolation distances for seed saving
| Item | Value |
|---|---|
| Seed depth | 1 to 1.5 inches |
| In-plant spacing | 8 to 10 inches |
| Row spacing | 30 to 36 inches |
| Days to maturity | 95 to 120 days, tie to silk and frost dates |
| Plants per 10 feet of row | 12 to 15 plants |
| Row length per person | 25 to 50 feet for ornamentals, more for heavy use |
| Isolation distance for seed saving | 250 to 660 feet depending on nearby corn |
Spot what went wrong, and fix it fast
Troubleshoot pale kernels, poor fill, cross pollination, tassel failure, and rot, with immediate fixes and what to accept as loss
- Pale kernels, uneven color, or chalky texture, cause, low phosphorus or late-season drought. Fix, side dress with a small amount of balanced fertilizer and water deeply. Accept that current ears may not improve, but future plantings will if soil is corrected.
- Poor kernel fill, cause, poor pollination. Fix immediately by hand pollinating the fresh silks for 2 to 3 days. Avoid single-row plantings next year, plant in blocks to improve natural pollination.
- Cross pollination, cause, other corn nearby. Fix, if you want pure glass gem seed next year isolate by 250 to 660 feet, or grow only one corn type and bag tassels for controlled pollination. Accept that seed saved this year may produce mixed colors.
- Tassel failure or late tassels, cause, cold snaps or heat stress during early growth. Fix for current season by hand pollinating when possible. For next year, plant later or earlier to avoid the stress window.
- Rot or ear mold, cause, wet conditions and poor drying. Fix, remove infected ears and burn or discard. Improve air flow and avoid overhead watering during silk stage. I lost a whole bed one year because I left flat rows with poor drainage, so next time I raised the bed and spacing and never had such a rot problem again.
FAQ
Is glass gem corn edible
Yes. Glass gem corn is edible. It is a flint corn that is best used dry for popcorn, grinding into meal, or for rustic cooking. You can pick it at the milky stage 18 to 24 days after silk for a starchy bite, but it will not be as tender or sweet as dedicated sweet corn varieties.
How long until glass gem corn is ready to harvest
Expect 95 to 120 days to maturity from planting, but tie harvest to silk dates and frost. For fresh eating pick 18 to 24 days after first silk browning. For drying harvest after husks and kernels are hard and dry, usually several weeks after silks brown and before the first hard frost.
Can I save seed from glass gem corn and keep the same colors
You can save seed, but only if you prevent cross pollination. Isolate by 250 to 660 feet from other corn or use controlled pollination. Keep records of planting date, neighbors, and pollen contributors. Even then, some color variation is normal in open pollinated corns.
How far away must other corn be to avoid cross pollination
Recommended isolation ranges from 250 to 660 feet depending on how strict you need true-to-type seed to be. Wind can carry pollen; 660 feet is safer if other corn types are nearby. If you cannot isolate that far, hand pollinate and bag ears to control parentage.
Can I grow glass gem corn in a large container
Growing in containers is possible but not ideal for seed saving. Use a container at least 15 gallons per plant and plant 3 to 4 plants together to aid pollination. Keep soil evenly moist and feed regularly. For higher success and easier pollination grow in the ground or raised beds. See container tips in my guide on how to grow tomatoes in containers.
One last note, if you are new to seed saving and want simple success, plant glass gem as an ornamental this year and practice seed saving on one or two isolated plants. Learn the timing, record what you did, and next year expand. For common pitfalls beginners face see common mistakes new gardeners make.
