Glasshouses that have the sole purpose of growing plants offer the most scope for growing humid and tropical ferns. Humidity levels can be raised with water trays, ‘damping down’ (where water is sprayed regularly onto a water-resistant floor to evaporate), ultrasonic humidifiers or pressurised misters, higher humidity levels being achievable as you work through this list. Humidity levels of 60 %RH is probably the minimum to achieve whilst some tropical ferns (and filmy ferns in cool houses) require levels of 80–95 %RH.

Heat can be provided by indirect methods such as hot water radiators or electric fan or convection heaters. What temperature is maintained depends on the requirement of the plants and reference to books on fern culture and to flora, defining the characteristics and altitude of the ferns’ natural habitat, will help to determine minimum day and night temperatures. Some ferns (such as tree ferns) require that the temperature has a diurnal variation with cooler nights than days.

 

More of a problem can be cooling the glasshouse in the summer, when temperatures can rise to high levels very quickly if the glasshouse is in direct sun. Ideally, glasshouses should have some degree of shading from trees or buildings and the resultant reduction in light levels will generally not harm ferns. Otherwise, shading will have to be provided by blinds, either external or internal. The level of light transmission should be 20–40 % but the shading should be capable of being removed in the winter months or on overcast days to allow extra light to enter. Heat reflective greenhouse paint on the glass can also be used, but this will need to be removed in winter.

 

Ventilation can also help control temperature but at the expense of humidity if simple evaporation systems are used. Automatic window opening systems are more reliable than manual. Ultrasonic humidifiers and misting systems can be set to operate when humidity drops to a pre-set level, although a reliable supply of suitable water is needed for both. Hard mains water and ion-exchange soft water can leave deposits of calcium and sodium on the plants respectively. Sodium salts can prove fatal to some ferns.

 

Light can be controlled by lowering and raising blinds and can be topped-up in winter months to extend the daylight hours to 12 or so. Intense LED bulbs give out virtually no heat and, although initially expensive, have very long lifespans. 

 

Finally, growing any plants in an artificial environment can lead to problems not encountered in the garden. The most obvious is pests and diseases which can thrive in a closed environment, especially if it is crowded. Please see the section on ‘Problems’ for more information on this.
 

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