For about 100 years the alpine house has played an important role in growing alpine plants. The most important feature of the alpine house is and will always be ventilation, as was the case 100 years ago. Many things contribute to creating the most effective alpine house. Through the years technical developments have made it possible for alpine houses to be built in a wide variety of designs.
Generally speaking, and alpine house is no more than a roof over the heads of extremely difficult plants that hate too much dampness. These are mostly plants that in nature grow in vertical crevices or even under an overhanging rock, in which case the cushion does not get wet at all. Alpine houses are the solution in these cases, as they enable plants to be grown plants under controlled conditions. It is, however, a pipe dream to suppose that all difficult alpines can now be easily grown in an alpine house. On the contrary, it is often advisable not to grow high alpines in a greenhouse. A good example is Androsace alpina, which does not stay neat and compact in an alpine house, where it is moreover bound to suffer from greenfly.
An alpine house is best positioned in an open site, to ensure light penetration from all sides. ( Light, after all, is the most important requirement for good growth). Any trees growing in the immediate surroundings will often result in green algae appearing on the glass and fallen leaves will block the drains in autumn. According to some theories the door should face a specific direction, but I do not think this is so. Light penetration and ventilation are the main considerations. The choice of materials for an alpine house is huge. Most alpine houses used to be built using cedar, and some still are. Cedar is a beautiful type of wood, longlasting and highly decorative. However, it is rather expensive. These days aluminium is a perfect alternative, now even available in a range of colours.
To all alpine houses that are for sale the same rule applies: they should meet the demands of the amateur growers, and be adapted to their needs. Saving money on ventilation is therefore not a good idea. It is best to have hinged roof opening lights and so-called louvre vents along the sides, at the height of the staging. The roof opening lights can sometimes be easily fitted with autovent openers to ensure optimum ventilation, an essential ingredient for alpine plants in the greenhouse.
In addition to ventilation, sufficient light is an important condition for your plants to thrive. If your greenhouse is bright enough you will get healthy, compact plants that flower abundantly, assuming the compost you use is of good quality. Sometimes too much brightness is harmful and you need to apply shading. Often a shading wash is used for this purpose. It is painted onto the outside of the glass, using a paintbrush, in early summer. The effect is a slightly milky-white glass, reflecting the sunlight, so that temperatures inside do not become excessive. The main disadvantage of this type of shading is that it reduces light penetration throughout the year, particularly in dull weather, when shading should be avoided because of low light levels. I therefore much prefer using gauze or slatted shades, attached to the outside of the greenhouse to prevent the glass from heating up. The great advantage is that it can be applied as and when actually required. Automatic slatted shades are even more effective. They have become more readily available for most people in the past few years. Prices of automatic control units comprising a so-called tube motor and sun and wind sensors are quite reasonable these days. These small computers can be fully programmed for light intensity and windspeed. A built-in delay prevents the motor from being activated any time there is the slightest breeze, or when a small cloud passes over the light sensor, thus avoiding continual turning off and on of the motor. If programmed correctly this system will ensure optimum shading, thus allowing the plants to benefit from the available light and keeping down the temperature in the greenhouse.
For many years now I have had automatically controlled mesh shades on both my alpine house and plunge bed, and neither has given any problems. The systems prove especially useful during working hours and holidays. In the past, without automation, I used to find that in some plants the growth had been drawn upwards because the mesh shades had been left on for too long, or alternatively plants had shown signs of scorch because the shades had not been put on at all. When I leave for work early in the morning it is, after all, difficult to assess if shading will be required during the day. Of course the amount of shading and the hours during which shading is required, is also determined by the type of plants grown in the alpine house. After all a Draba can stand more direct sunlight and heat than Saxifrages from the Himalayas.
Watering plants in an alpine house can be done in several ways. Much depends on the choice of pot : plastic or clay. Another decisive factor can be the time available. Many amateur growers water each plant individually. This, however, is not an option for everybody, especially when the large number of plants in your collection make it impossible for them to be inspected and watered one by one. I do consider this by far the best method, but unfortunately not applicable for me personally. Plastic pots can be placed on so-called capillary matting, which is kept moist. A layer of moist sand can be used for the same purpose, although a disadvantage is algae, mosses and liverwort developing on the surface. Clay pots can be used in the same way, or can be sunk into sand. The sand is kept slightly moist, allowing the roots of the plant in the porous clay pot to suck up the moisture. It is even possible to incorporate a capillary watering system into the benches. A water buffer ensures an adequate water supply for a longer period of time ( for detailed information on this system see AGS Bulletin vol. 65 no 2 pages 174 – 179). I have installed a capillary watering system in both the alpine house and the plunge bed, both functioning perfectly. When I am away on my travels my plants are provided with sufficient moisture for weeks on end. I have seen automatic systems being used by other amateur growers, to their complete satisfaction.
The alpine house as such has certainly undergone quite some changes in the past 20 years. Where in the past it was built in a more or less traditional way, these days other designs can be seen which add a new dimension to our hobby. The alpine house can be an architectural feature in our gardens, not just functional but also attractive. One of the best known and sensational designs is the Alpine House in Kew Gardens. This huge greenhouse was built in the shape of a pyramid and an unusual method was devised to cool the air inside it. A large concrete gutter was constructed all around the greenhouse, below the louvre vents. The air going into the greenhouse passes over the cold water and is thus slightly cooled. This, it is hoped, makes for an more easily controlled temperature inside. Of course there are numerous ventilation lights in the roof and the sides. Another option is to sink your alpine house into the ground, thus making it less conspicuous in the garden. Another great advantage of this approach is that it allows for better temperature control inside the greenhouse. The greenhouse will stay cooler in summer and warmer in winter. The soil around it will act as a heat buffer. The benches, which are at ground level, seem to form a whole with the surrounding garden. There are even examples of this type of alpine house being used in gardens where they are completely integrated in the layout and the roof of the alpine house only serves to indicate the location of the more demanding plants. Standing on the sunken path of such a greenhouse you have an excellent view of the plants inside as well as those in the garden.
In several alpine houses completely natural-looking tufa cliffs have been constructed. Tufa slabs, stacked face to face and set up on edge can be used for the purpose of building such fine-looking cliffs. A lot of time and energy will go into constructing them, but the final result will be there forever. If you incorporate a seep hose, watering will no longer be a problem.
Instead of glass so-called Macrolon or polycarbonate sheets are now used. A great advantage is that these are lightweight, unbreakable and that they transmit light very well. A major drawback is that they are expensive, ranging from £ 25 to £ 30 per square metre. Should you wish to make use of these sheets, make enquiries first! Some sheets let U.V. light through, others block it. Of course, the first type is to be preferred for our high alpine plants. The sheets are 16 mm thick and available in several widths, standard length 6m. It is even possible to buy double-walled sheets, thus providing additional insulation. The effect of this type of sheet may be compared to that of double glazing. Light penetration of these polycarbonate sheets is quite good, only a small percentage of light is lost. With the use of these sheets scorch is much less frequent in the greenhouse than with ordinary glass, which heats up quickly. The sheets provide insulation in summer as well as winter. Since the material is lightweight, yet very strong, beautiful greenhouses can be built with it. I saw an example in Germany where the tall hinged lights on the sides, made of double-walled polycarbonate sheets, were opened up to 90° from April to October, perfectly protecting the Juno irises growing under them from the rain, thereby giving them the rest they need in summer. In winter the lights are closed again, helping the Dionysias in the greenhouse through the winter.
Methods and materials are so diverse nowadays that we are bound to see many innovative designs for greenhouses after the year 2000. It is up to everyone personally how far they wish to go in trying to grow their plants in the best possible way. Some will be happy with a simple greenhouse, others may even wish to install airconditioning in their alpine house. What would you think of a roof that slides open automatically and only closes when the rain sensor detects a drop of rain!? Only time will tell.
Look for pictures at: IMAGES –> GALLERY –> My Garden, or click here.