Shade-house modifications to increase winter temperatures
A larger range of orchid species can be grown in cool climates if the effect of frost and low winter temperatures is mitigated by covering the shade-house with plastic during the colder months. In this case a roll of 200μm thick clear plastic film is wrapped around the shade-house and secured with velcro and eyelets. The shade-house has a permanent polycarbonate roof.
The low cost builders plastic film is added in mid May and removed in late August. The plastic should last several seasons if not exposed to UV radiation over summer. Heavy duty nursery grade plastic film could also be used and may last longer.
The plastic film raises night temperatures by about 1-2°C which is sufficient to avoid frosts in this inland region. Daytime temperatures are typically 6-10°C higher inside the shade-house during winter with the film added, greatly extending the period during the day of favourable temperatures (see graph below). The plastic film only raises daytime temperatures on sunny days, it has no effect on cloudy days, although can still have a small beneficial effect at night.
Orchids are more likely to tolerate low night temperatures in winter if daytime temperatures are substantially higher. The risk of frost damage is also greatly reduced by the plastic film with the night temperature not falling below 1°C in winter when outside temperatures fell to -2°C.
In this case only a single layer of plastic was used. Better insulation would be achieved if a double layer of plastic was used with an air gap between the two layers. Bubble wrap would also be expected to convey better insulation than a single layer of plastic.