Corn is unusual among garden plants because its male and female flowers grow in separate places on the same stalk: pollen at the top, ears lower down. Every kernel on an ear exists only because one silk caught one pollen grain falling from above.1Agronomy Dept., Purdue Univ.. Flowering Corn: The Tassel and Silk Process Explained2Purdue University Agronomy Dept. Flowering Corn: The Tassel and Silk Process Explained The whole exchange runs on a tight clock, which is why the weather during a single week or two of summer can decide how full your ears turn out.
How the Tassel and Silks Divide the Work
The tassel is a branched cluster of male flowers, each holding small sacs called anthers that make pollen. Inside each anther, the pollen grains develop over many stages and fill with starch before they are ready.3PubMed Central. Genetic Structure and Molecular Mechanisms Underlying the Formation of Tassel, Anther, and Pollen in the Male Inflorescence of Maize When the grains are mature, the anthers split open and release them into the air.4PubMed Central. Genetic Structure and Molecular Mechanisms Underlying the Formation of Tassel, Anther, and Pollen in the Male Inflorescence of Maize Most tassels shed over roughly a week, with the heaviest shedding in mid-morning.
The silks that emerge from the ear tip are the working stigmas of the female flowers.5Agronomy Dept., Purdue Univ.. Flowering Corn: The Tassel and Silk Process Explained Each kernel spot on the cob begins as a tiny female flower, and each of those flowers grows its own silk, so the silks you see are a bundle of individual threads rather than one structure. A silk that never catches pollen leaves an empty spot where its kernel would have been.
The silks must grow out through the opening in the husk leaves to reach open air where pollen is falling. Silks from the base of the ear are the longest because they travel farthest. Those from the tip are shorter and emerge last, which is why tip kernels are the ones most likely to be missed. Silks are living flower parts, and pulling or cutting them early can stop kernels from forming.
The two organs are easy to tell apart. The tassel sits at the very top of the main stalk, while the ear forms on a short side branch partway down. A stalk usually carries one tassel and one or two ears, and the topmost ear normally fills best.
Over a few days in the garden, you will see tassels appear first, usually a few days before silks show. Yellow dust on the leaves below the tassel means pollen is shedding. Fresh silks are pale green or cream and look moist; they turn brown and dry once their job is done or they age.
How Long Pollen and Silks Stay Viable
Corn pollen leaves the anther about half water, around 55 to 60 percent moisture.6Field Crops Research. Relationship between desiccation and viability of maize pollen It dries out in the air at a rate set by temperature, humidity, and time.7Field Crops Research. Relationship between desiccation and viability of maize pollen Once its moisture falls to about 30 percent, it can no longer grow.8Field Crops Research. Relationship between desiccation and viability of maize pollen In the field, that means pollen usually stays viable for only 1 to 2 hours after release.9Crop Science. Maize Pollen Longevity and Distance Isolation Requirements for Effective Pollen Control Depending on weather, half of it loses its ability to sprout within 1 to 4 hours.10Agricultural and Forest Meteorology. Survival of maize (Zea mays) pollen exposed in the atmosphere Drying, not sunlight itself, is what mainly kills it.11Agricultural and Forest Meteorology. Survival of maize (Zea mays) pollen exposed in the atmosphere
That is why hot, dry afternoons matter more than bright sun: low humidity speeds drying and shortens pollen’s working life. It is also why morning is the most useful time to hand pollinate.
You can check whether pollen is shedding on a given morning by tapping a tassel branch or running a hand along it. A puff of yellow dust, or a dusting on your palm, shows the anthers are open. Shedding usually starts once the dew has dried from the tassel, so a wet or cool early morning pushes it later.
Silks offer a longer, closing window. All the silks on one ear usually emerge over about 4 to 8 days.12Crop Science. Emergence, Elongation, and Senescence of Maize Silks They grow fastest on their first day out and stop growing within 9 to 11 days.13Crop Science. Emergence, Elongation, and Senescence of Maize Silks But silks begin to wither about 7 to 8 days after they appear, and the first ones out wither first.14Crop Science. Emergence, Elongation, and Senescence of Maize Silks So the silks from the cob’s base, which emerge first, are the first to lose their chance.15Crop Science. Emergence, Elongation, and Senescence of Maize Silks
Because silks come out over days, base kernels are set earliest and tip kernels last. A good stand sheds across several days, so later silks still get covered. A short burst of pollen early on can leave late silks with nothing, so pollen has to keep coming for several days.
From Pollen Grain to Kernel
Pollen is heavy for a wind-carried grain.16Journal of Aerosol Science. Settling speed of corn (Zea mays) pollen It falls quickly, and most lands close to the plant that shed it.17Field Crops Research. Lagrangian numerical simulations of canopy air flow effects on maize pollen dispersal A grain that lands anywhere along a receptive silk sprouts within minutes.18Purdue University Agronomy Dept. Flowering Corn: The Tassel and Silk Process Explained It grows a tube carrying the male genetic material down inside the silk.19Purdue University Agronomy Dept. Flowering Corn: The Tassel and Silk Process Explained The pollen coat carries an enzyme that helps the tube push into the silk.20PubMed. Maize pollen coat xylanase facilitates pollen tube penetration into silk during sexual reproduction The tube reaches and fertilizes the ovule within 24 hours.21Purdue University Agronomy Dept. Flowering Corn: The Tassel and Silk Process Explained
Many grains may sprout on one silk, but typically only one fertilizes the ovule.22Purdue University Agronomy Dept. Flowering Corn: The Tassel and Silk Process Explained Fertilization is double: one sperm makes the embryo and another makes the starchy endosperm that fills most of the kernel.23Seed Biology. Current Advances in Maize Seed Biology The pollen’s genes can also slightly change the kernel itself, making cross-pollinated kernels up to about 13 percent heavier in some inbred lines.24Crop Science. Xenia Effects in Maize with Normal Endosperm
Because pollen shapes the endosperm, pollen from nearby field corn or popcorn can alter sweet corn kernels the same year. Mixed-color kernels on an ear can be a visible sign of crossing. Gardeners often separate different types by distance or planting time.
A fertilized silk usually detaches and dries from the base within days. Silks still fresh and clinging after a week may have failed to catch pollen, though this is only a rough clue.
A silk that catches nothing keeps growing longer than its neighbors until it is pollinated or ages out. Its kernel spot never fills. Every silk acts alone, so a few misses don’t ruin an ear, but many misses scatter gaps across it.
Why Heat and Drought Leave Gaps on the Ear
Drought just before or during flowering delays silk emergence while pollen shed continues.25PubMed. Identification of quantitative trait loci under drought conditions in tropical maize. 1. Flowering parameters and the anthesis-silking interval The gap between pollen shed and silking grows longer.26PubMed. Identification of quantitative trait loci under drought conditions in tropical maize. 1. Flowering parameters and the anthesis-silking interval Silks may then appear after most pollen is gone, leading to failed pollination and lost yield.27PubMed Central. Overexpression of ZmEXPA5 reduces anthesis-silking interval and increases grain yield under drought and well-watered conditions in maize Drying silks stop growing altogether when they lose enough water.28Crop Science. Water Deficit Affects Receptivity of Maize Silks In dry conditions, hybrids whose gap stretched the most also lost the most grain.29Field Crops Research. Grain yield, anthesis-silking interval, and phenotypic plasticity in response to changing environments: Evaluation in temperate maize hybrids
When soil moisture drops, the plant sends water first to keeping its leaves alive, so the growing silks are shorted and emerge late or stay short inside the husk. The tassel is higher and develops earlier, so its shed can stay on schedule while the silks lag. Leaf rolling in the afternoon is a visible sign of stress, and a cue to water if silking is near or underway.
Heat does its damage inside the silk. Heat right after pollination can cause kernels to fail within 6 hours.30PubMed. Heat-dependent postpollination limitations on maize pollen tube growth and kernel sterility It mainly slows the early growth of the pollen tube, not the sprouting of the grain.31PubMed. Heat-dependent postpollination limitations on maize pollen tube growth and kernel sterility Moderate heat can also damage the silk and stop pollen tubes late in their journey.32PubMed Central. Heat-stress-induced ROS in maize silks cause late pollen tube growth arrest and sterility Even after fertilization, kernels can abort over the next 1 to 2 weeks when the plant can’t supply enough sugars, a problem heat makes worse.33PubMed Central. Roles of carbohydrate supply and phytohormones in maize kernel abortion34PubMed Central. Heat Stress After Pollination Reduces Kernel Number in Maize by Insufficient Assimilates
Heat and drought often arrive together. Hot, dry air speeds the drying of pollen, so less viable pollen is around just when silks are struggling. A plant short of water also cools itself less, so its tissues run hotter and add heat damage on top of the drought. Fewer silks catch pollen, and of those that do, fewer tubes finish their trip.
The two weeks around silking are the most sensitive time in a corn plant’s life. Stress before tasseling mostly reduces plant size, while stress at silking cuts kernel number.
After harvest, the ear tells you what happened. Scattered missing kernels often point to poor pollen coverage, though other causes such as pests or kernel abortion can look similar. A bare tip often means late silks missed pollen or kernels aborted. Kernels that started and then shriveled suggest stress after fertilization rather than missed pollination.
Getting Full Ears in a Home Garden
Since most pollen settles close to its source,35Field Crops Research. Lagrangian numerical simulations of canopy air flow effects on maize pollen dispersal corn planted in a single long row often pollinates poorly. Plant a block of at least four short rows instead. A square or rectangle lets pollen from any tassel fall on the silks of many neighbors rather than drifting off past the end of a row. Space plants as the seed packet suggests, so the block is dense enough to share pollen without the plants competing for water. In a tight space, a few clumps of closely spaced plants beat one long thin line.
Keep different corn types apart, or stagger their planting so flowering doesn’t overlap. Sow the second type a couple of weeks later, so its tassels shed after the first has finished silking. Staggering also stretches your harvest of fresh sweet corn.
Because drought delays silks,36PubMed. Identification of quantitative trait loci under drought conditions in tropical maize. 1. Flowering parameters and the anthesis-silking interval water deeply when tassels first appear and through silking. An inch of water a week is a common garden guideline for corn at this stage. Water slowly at the base so the soil is wet several inches down, rather than sprinkling lightly each day. Push a finger a few inches into the soil and water when it feels dry there. A deep drink before a forecast hot spell helps the plant keep its silks growing and cool, and mulch keeps soil moist through the heat.
If pollination still looks thin, you can hand pollinate. Wait until mid-morning, when pollen is shedding and the dew has dried. Shake a tassel over a paper bag, or bag it, to collect pollen. Sprinkle it onto the silks right away, since it lasts only an hour or two. Repeat every day or two while the silks are fresh.
Some well-meant habits cut pollination. Removing tassels to “help the ears” leaves no pollen. Overhead sprinkling during heavy morning shed can wash pollen off. Planting too few plants gives too little pollen to cover all the silks.
Smut and Ear Rot That Enter Through Silks
The same silks that carry pollen tubes to the kernels also give fungi a path into the ear.37PubMed Central. Fungal Pathogens of Maize Gaining Free Passage Along the Silk Road Ear rot fungi enter through silks and can leave toxins harmful to people and livestock.38Pathogens. Discovery and testing of pollinated maize silk-associated microbes including microbiome assisted selection of biocontrol agents against Fusarium graminearum Common smut can grow down silks into kernels, forming swollen galls at the ear tip.39Pioneer. Tips for Managing Common Smut in Corn Silks left exposed longer before pollination give the fungus more chance to get in.40Pioneer. Tips for Managing Common Smut in Corn
Smut shows up as a puffy, silvery-white gall that replaces kernels. It often bulges from the ear, or appears on stalks and leaves, and later turns black and powdery inside. Ear rot looks different: fuzzy mold in pink, white, green, or dark colors growing on and between kernels, often starting at the tip.
The two call for different handling. Remove smut galls before they burst to reduce spores next year. Young, firm galls are eaten as a delicacy in some places, but only while they are still pale and not yet dusty with spores. Moldy ears are another matter, because the molds can produce toxins. Discard ears with pink or moldy rot rather than eating them or feeding them to animals, and if you are unsure what you have, discard the ear.
Kernels on the Tassel and Other Odd Flowers
Each young corn flower starts with both male and female parts, and the plant switches one off. In the tassel, hormones normally shut down the female parts.41PubMed Central. Hormonal influence on maize inflorescence development and reproduction When that shutdown fails, the tassel grows kernels, a condition called tasselseed.42PubMed Central. Hormonal influence on maize inflorescence development and reproduction Some dwarf corn with low levels of one growth hormone also forms kernels on its tassels.43PubMed Central. Brassinosteroid control of sex determination in maize High levels of another hormone, gibberellin, push flowers toward female.44PubMed Central. Factors specifying sex determination in maize
Tasselseed appears as small kernels, often with silk-like threads, on the branches of the tassel in place of the usual pollen-shedding flowers. Those flowers turned female, so they produce no pollen.
In a garden, occasional kernels on the tassels of side shoots are common and harmless. They are edible but usually small and few. A whole planting showing tasselseed may point to a variety trait or early stress.
Day length also affects when corn flowers. Corn from tropical areas can flower late in long northern summers, while modern varieties carry gene changes that make them flower regardless of day length.45PubMed Central. ZmCCT and the genetic basis of day-length adaptation underlying the postdomestication spread of maize Choosing varieties suited to your region helps flowering land in good weather.