In a greenhouse it is essential to have adequate ventilation and over the growing season appropriate shading. From spring to early autumn apply a shading wash to the outside of the glass so that plants are not stressed unnecessarily by extreme weather conditions. Additional protection can be added by mounting shade cloth on wire, which can be withdrawn during dull weather.
Protect leafy cuttings
Even if they are in the greenhouse, leafy cuttings need extra protection as they initially have no roots and cannot easily take up water to replace that lost from the leaves. You can cover them with clear plastic sheeting or a plastic bag. Place it over the tray of cuttings and tuck it under. Soft cuttings may succumb to disease if the plastic touches them. Insert a framework of split canes or wire in the compost to keep the plastic off the cuttings. Keep the containers in a shaded but light place out of the sun to avoid excessive air temperatures. If you are using rigid plastic propagators you should also shade them. Initially keep the vents closed to maintain the moist atmosphere, and once the roots appear and the cuttings are ready to be harden off you can open the vents.
A mist unit provides the best system for summer propagation but for winter and early and late season propagation it should be combined with bottom heat. For softwood cuttings, which wilt readily, it is best to arrange a low, clear plastic tent just above the misting nozzles. This will ensure a higher ambient humidity between mist bursts than open mist does. It is important to shade this system also in bright weather.
Most biological processes are speeded up when temperatures are higher. Raising compost temperature usually increases the rapidity with which seeds germinate and cuttings root. For small greenhouses it is most convenient to use cables or heating mats. The temperature is controlled by a rod thermostat, but during bright conditions the air temperatures may build up in a closed mist system, so you will have to switch the heat off during these periods.
Hot-pipe callusing applies thermostatically controlled hot air to a grafted plant to speed the formation of callus tissue, which is the first sign of a successful graft union. If the temperature within the pipe is set to 20-25 Celsius degrees (68-77 F), callusing should occur within a few weeks.
These self-contained units are useful mainly for extending the propagation season. Since the units have heat loadings well in excess of the 160watts/sqm recommended for mist systems, they must be fitted with effective thermostats or else the high temperatures may damage the cuttings in sunny weather.
These provide a valuable gain in soil and air temperatures while maintaining high humidity and providing adequate light for young plants. They can be used to raise seedlings early in the season, to protect grafts and to propagate leafless and leafy cuttings. They may also be fitted with bottom heat if needed. Because they have no great volume, they easily overheat in sunny conditions so they need to be well ventilated and shaded. When temperatures falls below -5 Celsius degrees (23 F), cold frames must be insulated with thick layers of Hessian, coconut matting, polystyrene tiles or bubble plastic.
Cloches and polytunnels
Glass and plastic cloches and tunnels are most often used to give seedlings an early start in the season in the vegetable garden. A wide range of easily rooted cuttings also do well in such an environment, as long as additional shading, such as shade netting, is used in bright, sunny weather.