14:37 - 11 June 2010
A greenhouse allows the gardener to extend the growing season at both ends and to grow and protect plants throughout the year, Different plants need different light levels to flower, fruit and set seed and some plants positively thrive in extreme heat and high light levels. Most greenhouses are positioned in the garden to make the most of natural sunlight. In winter especially when the light is low, the glass panels accentuate the rays providing protected plants with precious sunlight. As the season progresses and the daylight hours extend, temperatures in the greenhouse can reach sky-high levels which some plants just can’t tolerate.
Greenhouse gardeners employ several methods to keep their plants comfortable throughout the summer. With adequate and generous ventilation it is possible to keep the conditions in the greenhouse ideal for most plants, couple that with efficient watering and your plants will simply thrive in their warm, glasshouse conditions.
But in exceptional weather and when the ventilation and watering is simply not adequate plants can overheat and die. Some plants that hail from desert conditions such as cacti and succulents simply thrive in these conditions, while others do need protection.
Most greenhouses benefit from a degree of shading in the summer months to limit the solar energy absorbed by the glass. There are several ways to shade a greenhouse and the choices are usually dependent on the budget available and the final look of the greenhouse when shaded.
By painting the glass panes of the glasshouse with a special shading liquid, usually white, it reflects the sun’s rays off the glass and shades the plants inside. The drawbacks are that it can wash off in heavy rain, it is fiddly to apply, especially if you have a large glasshouse, it can look unsightly and it needs polishing off for the winter so that your plants get enough light to grow.
This sort of shading is ideal for the allotment greenhouse or the budget greenhouse where looks aren’t too important and budgets are tight. It works well and is cost effective.
For the feature greenhouse where the glasshouse forms a central part of the garden and its looks are important, you need to invest in some blinds. Ideally these are fitted outside the greenhouse so that they block the sun’s rays before they hit the glass. The ultimate exterior blinds are automatic which ensures that your plants get the full benefit of the daylight at either end of the day. These are usually triggered by light sensors that unroll or retract the blinds as the sun rises and sets. This is particularly useful if you aren’t able to attend to your glasshouse daily. Make sure that these blinds are protected from extreme weather and avoid setting them up on exposed greenhouses and do not fit them on a greenhouse roof where automatic vents are in operation as they will become entangled in the blinds. Fitting blinds over any vents will obstruct the airflow, so some careful planning is required.
If automatic blinds are out of your price range then look for slatted blinds that can be rolled or unrolled manually over the greenhouse glass. This blocks the sun rays from the glass and prevents heat building up in the greenhouse. you can leave them urolled if there is a spell of hot weather forecast, or roll them back up if the weather partterns change and cloud and rain are forecast. For the best results use exterior and interior blinds on the south facing windows and manually alter them to suit the needs of your plants. Interior blinds can get in the way of growing plants.
Slatted blinds allow some light through but can also be closed in extremely bright or hot weather. If budget allows these can be made especially for your glasshouse.
For greenhouse gardeners on a budget, cost effective screening can be made from rolls of reed screening, hessian, or canvas, draped over the south facing side of the glasshouse. These need to be secured to the frame with strong clips, or you could make large framed sheets of fabric and hang these from the apex. Bear in individually the weight of the material and how it will cope with wind and rain and choose carefully.
Temporary shading can also be fitted to the inside of the glasshouse.
