After Lammas corn ripens as much by night as by day.

The saying observes that, once the Lammas season has arrived, grain is believed to move rapidly toward full ripeness. Growth or change is pictured as continuing with equal force through the night as through daylight.

It stresses the swift final stage of maturation rather than a literal comparison of measured hourly growth. What has already developed far enough can seem to advance almost continuously until it is ready for harvest.

Use it when speaking of grain nearing harvest and appearing to ripen very quickly. Agricultural timing is seasonal and may not match every climate or crop-growing area. It can also be applied cautiously to another process in a visibly fast final phase of development.