A poly-propagator is an appropriate technology for multiplying plants that are most easily propagated under very humid conditions. Poly-propagators have a frame constructed with wire, bamboo, wood, or other supportive materials. Use what you have!
The exterior of poly-propagators is made of clear plexiglass or polyethylene as you can see from these two examples. If you build it with polyethylene, use plastic with a thickness of 6-8 mil.
The bottom few centimeters of the poly-propagator should be leak proof and able to hold the water needed to keep plant material moist.
These structures provide constant moisture and maintain up to 95% humidity, increasing the propagation success of hardwood and semi-herbaceous cuttings.
ECHO North America uses polypropagators for crops such as passionfruit, bay leaf, Barbados cherry, figs, and katuk. A slit through the plastic (or hinge on a wooden frame) gives access to work with the propagation material. A loose opening allows you to maintain elevated humidity levels inside the polypropagator with minimal risk of overheating.
Typically, growers will place sand at the bottom of the poly-propagator followed by gravel and rooting medium in which plant propagation material is grown. Water in the sandy layer wicks upwards to the rooting media above.
At ECHO North America we root cuttings in media placed into germination trays instead of media placed directly in the poly-propagator reservoir. The germination trays are placed on top of upside-down trays that act as a stand to keep the bottom of the germination trays near the top of the water line in the reservoir. We use the upside-down trays as stands because they don't add a lot of weight to the poly-propagator but you could also use other materials such as rocks or pieces of wood. The water reservoir is maintained so that water can wick up into the germination tray without cutting being submerged. Always water propagation material in a poly-propagator from the bottom to minimize leaf wetness and splashing of media onto plant material which can spread disease. Sterilize your poly-propagator with a diluted vinegar or isopropyl alcohol spray between uses and remove all water and plant residue before introducing a new batch of plants.