Why Are My Corn Cobs So Small and Undeveloped?

A corn cob that barely reaches ten centimetres when it should be twenty-five, with thin kernels or many gaps, has fallen short somewhere in the chain of events between pollination and kernel maturation. Corn cob size and fullness are determined by how many kernels were successfully pollinated, and how much energy the plant was able to channel into filling them during the six weeks after silking. Both factors are controllable.

Poor pollination producing small cobs

Corn is wind-pollinated. The tassels at the top of each plant shed pollen that must land on the silks of the same or a neighbouring plant. In a small garden with only a few plants, or when plants are in a single long row rather than a square block, pollen dispersal is inefficient and many silks receive no pollen at all — those silks produce no kernels, leaving a small, gap-filled or very short cob. Plant corn in a square or rectangular block of at least four rows, minimum three plants per row, for reliable cross-pollination. In very small spaces, shake the tassels over the silks by hand during the morning when pollen is being shed.

Drought during kernel fill

The kernels develop and fill with starch and sugars over six weeks after silking. Any prolonged drought during this period limits the photosynthate available for filling and produces small, lightweight kernels. The cob may look full in terms of row number but the individual kernels will be thin and lightweight. Water consistently and deeply through this period.

Overcrowding reducing energy per plant

Corn grown too densely produces more, smaller cobs — or just one small cob per plant — as the plants compete for light, water and nutrients. Plant at 30–35 cm spacing within rows, with 60–75 cm between rows. This spacing gives each plant enough canopy to capture the sunlight it needs for full cob development.

Short season and late maturity

In a short cool season, cobs may have started developing normally but run out of warm days before completing fill. Growing early-maturing varieties suited to your climate is the main remedy for this.