Why Are There Gaps of Missing Kernels on My Corn Cob?

A corn cob with scattered gaps — bare patches where there should be plump kernels — is a pollination problem. Every kernel on a corn cob corresponds to a single silk thread that was successfully pollinated by a pollen grain. Where a silk received no pollen, the potential kernel aborted, leaving a gap. Understanding how pollen and silks interact tells you exactly why gaps appear and how to prevent them.

One row or a small patch — the core problem

Corn is wind-pollinated, and pollen falls from the tassels downward and to the side. In a long single row, most pollen blows away rather than landing on silks. In a block — at least four short rows wide — pollen from surrounding plants is constantly landing on every plant's silks and pollination is thorough. This single layout change, from a single row to a block, eliminates most gap problems in home gardens immediately.

Timing mismatch between tassels and silks

Within a single variety, tassels typically shed pollen for about ten days and silks are receptive for a similar window. Normally these overlap well. If the tassels have finished shedding and the silks appeared late — which can happen in a late-season cold snap or in plants that developed unevenly — some silks may have been exposed only to old or depleted pollen. Growing a block of plants of the same variety sown at the same time ensures all plants are at the same stage simultaneously.

Wet weather washing pollen away

Pollen shed during heavy rain is washed off the silks before it can fertilise them. A week of wet, overcast weather during peak silk emergence produces patchy pollination and gaps in the resulting cobs. There is not much to be done about the weather, but hand-pollinating — snapping off a tassel and dabbing it directly on the silks of neighbouring plants — during dry morning hours supplements natural pollination in wet summers.

Insecticide damage to silks

Some insecticides, and particularly misapplied horticultural oil or soap sprays, can damage or desiccate silks, reducing their receptivity. Never spray anything on corn plants while silks are actively extending and visible. Wait until the silks have browned and pollination is complete before applying any treatment to the plant.