A seed spacing monitoring system is used In an agricultural seeder for planting seeds. The agricultural seeder has a furrow opener, a seed meter for metering seed to be dispensed in the furrow, and a furrow closer to cover the seed in the furrow. The seed spacing monitoring system includes a detector supported to detect seeds in the furrow prior to the seeds being covered. The detector provides a plurality of seed presence signals, with each seed presence signal being indicative of a respective seed present in the furrow. A speed sensor is associated with the seeder and provides a speed signal indicating a ground speed of the seeder. An electrical processor receives the plurality of seed presence signals and the speed signal. The electrical processor determines a seed spacing, dependent upon the seed presence signals and the speed signal.