One of the most important aspects of successful seed germination and cutting propagation is management of the temperature of the growing medium.
Bottom heat can be controlled by electric mats for small areas, but re-circulating hot water systems are most common in commercial production systems.
Hot water system under the bench.
Recirculating hot water systems provide uniform bottom heat for seeds or cuttings. Hot water from a water heater is forced through small tubes that run throughout the bench top. A thermostat controls the water temperature. It is located on the bench to check the temperature of the medium.
The effective temperature maintained by this type of system is between 75 and 85°F (24-30°C).
Similar hot water systems recirculate under ground bed propagation.
In some cases, the entire greenhouse floor is heated and container-propagated plants are placed on top of the floor.
Otherwise the propagation medium is heated and cuttings stuck directly in the ground beds.