The structures that serve as production facilities for greenhouse and nursery growers also serve for propagation. Greenhouses, hotbeds, cold frames, and lath houses (see Chapter 19) can all be used directly or in some modified manner to propagate plants.

The propagation structure must possess the following four charac­teristics:

1. Sufficient light or darkness to permit seed germination and photo­synthesis

2. High humidity to reduce wilting of the cutting until new roots can form and to promote callus tissue formation in grafts

3. Warmth, to accelerate germination or rooting

4. Ventilation, once roots have been formed, to reduce the risk of disease

figure 14-1. The mist from the overhead line is retained by the plastic curtain. This is a typical propagation bench. (Delmar/Cengage Learning)

Since plant propagation usually requires higher temperature and greater humidity than general crop culture, the grower may designate certain structures for propagation only. Where the quantity of plants propagated does not justify an entire greenhouse or frame, one or two benches may be used as propagation chambers. With a timed mist line to provide the moisture, and a covering of transparent polyethylene film draped on wires over the bench to retain the humidity, an excellent propagation bench can be created (Figure 14-1). The plastic canopy can be folded back at night permitting the cuttings to surface-dry, thus reducing the risk of mildew and other diseases. In such a situation, it is critical that the media used and the benches assigned for propagation be pasteurized and well-drained.