Unit planters are self-contained, single-row units mounted on a toolbar. A unit planter consists of a hopper, furrow opener, seed placement tube, furrow closing device, and a press wheel. The press wheel normally operates the seeding system through a chain drive. The seed metering system uses a variety of plates and/or other mechanisms to supply single seeds uniformly spaced at accurate depths. Each planter is independently suspended so it can closely follow varying terrain. Additional hoppers are available for granular fertilizer, inoculum, or pesticides. In some cases, a spray nozzle is attached to each planter to apply pesticide in a band over the row. Numerous types of coulters and row sweeps are available to improve efficacy in no- or limited-till conditions. Planting units can vary in width up to 90 feet by using a flexing toolbar. Distances between individual planters can be adjusted for specific crops and can vary between 15 and 40 inches.
Unit planters are precision seeders that were originally designed to operate on clean-tilled land. However, due to conservation requirements, planters have been redesigned to operate in moderate to heavy crop residue. Unit planters are used where precise seed depth and spacing are important and should not be used where rocks and brush debris are present.