Shading and Ventilation in the Greenhouse
During the summer mostplants, with the exception of cacti and other succulents, will require some shading from direct sunlight. Plants which ‘scorch’ easily include the begonias, especially the large double-flowered and winter-flowering types, gloxinias, streptocarpus, Fuchsias, ferns, orchids, African Violets, young poinsettias, eedlings of many plants, unrooted and newly potted plants. Sunshine beating through clear glass can raise temperatures to unacceptable heights very quickly and this is something the greenhouse gardener has to reckon with during the warmer months of the year. Fortunately there are numerous ways and means of coping with this problem, some more sophisticated and therefore more expensive – and by the same token more efficient and allowing greater control – than others.
The most simple way to provide shade in a greenhouse is to paint the glass with whitewash. Plain whitewash made with lime and water will wash off fairly quickly but if just a little size is added it will adhere much better. An alternative is to make use of one of the proprietary shading compounds, available from any garden sundries store or garden centre.
Shading can be stippled on the glass with a brush, but this should only be applied lightly so that it breaks the rays of the sun without excluding too much light.
The drawback to coating the glass in this way is that the shading is permanent, and cannot be altered to suit changing
A capillary bench watering system is a boon for the busy gardener. Water is supplied automatically, in this case from an inverted conditions. This is where blinds that can be lowered or raised at will have an advantage. Fabric or polythene blinds are excellent for internal use, but if blinds are to be fitted outside the house, it is better to choose those made of wooden laths – preferably cedar wood – or split cane. These are really ideal for they provide a mottled shading which gives a barrier against the sun but again lets a lot of light through. Another way to provide shade, in the absence of blinds, is by means of very line nylon netting.
Of course, the ultimate is to have automatic blinds. Wooden lath blinds are available for exterior fitting which will roll and unroll automatically by electric motor, the electric current being activated by a thermostat or photo-electric cell. For the busy greenhouse owner who is away from home for long periods of time during the day, the advantages are obvious. In combination with automatic heat control and watering it can indeed be a real boon.
One other use for blinds should be mentioned here their use to keep heat in the greenhouse on really cold winter nights as opposed to keeping heat out on sunny summer days. This can be important. Not least in saving fuel where the temperature is maintained at a set level by thermostatic control.
Frames can also be treated with white-wash or proprietary shading compounds. A more temporary expedient, which may be preferable where the need for shading is short term, is to cover the lights with bottle, to the sand beds on which the pots stand, and the plants obtain their water by capillary action green polythene, hessian or newspaper kept in place by bricks or other suitable objects.