Friday, June 8, 2007

Greenhouse for Cacti

If you're a cacti & succulent lover and collect many collections of those plants, you may need to have a greenhouse because the plants always want to be kept in the warm temperature. Sometimes, it's really impossible in your country. Meanwhile, the greenhouse can keep your plants from rain, humidity and even snow.


A greenhouse positioned so that the ridge runs in an east-west direction will receive more winter light, which could be useful if it is to house mainly succulent plants that grow during the winter. In either case, it is best to avoid locating a greenhouse where it will be in shadow for a substantial part of the day, to near to trees or in areas subject to strong winds. Positioning the door away from the prevailing wind will help to reduce drafts. Areas of land subject to local flooding should also be avoided. If the greenhouse is sited too far away from the house it may be difficult or expensive to provide supplies of electricity or gas.

Greenhouses either have an integral base, or need to be erected on a purpose-built base. A solid floor provides a clean surface under foot and helps to keep out pests. It is an advantage if a solid base slopes slightly to encourage water to drain away. Drainage channels may be moulded in to the concrete to direct water out of the building. However, if you want to plant larger columnar cacti into the ground, then foundations should be constructed around the planting area. Construction of the greenhouse frame needs some thought. For example, should it be made of wood or metal? Both types have their proponents. Wood has a "natural" look and blends in to a garden landscape, but may be subject to attack by insects, tends to rot in humid climates and therefore has a limited life and needs substantial maintenance. However, hard-woods such as cedar mitigate these problems.

Aluminium frames tend to conduct away heat and are therefore harder to keep warm than wooden greenhouses. However, they are relatively low maintenance and should last well. Some modern aluminium frames incorporate thermal barriers.The greenhouse is traditionally glazed with horticultural glass, which contains less trace colourants (such as iron) and transmits more light than ordinary window glass.

Newer materials such as UV-stabilised acrylic plastic are also suitable and conduct away less warmth than glass. However, some plastics may exude phytotoxic vapours, so always use grades designated as suitable for horticulture. Various double-skinned products are available, but these may reduce the amount of light available to plants, which is always at a premium in countries such as the United Kingdom. This is also a problem with wire-reinforced glass, often used as a roofing material.
As with the greenhouse frame, staging can be made of wood or metal, with similar advantages and disadvantages of the materials. After watering, plants become very heavy in their pots. Clay pots are heavier than plastic ones and a peat-based compost is usually lighter than one based on loam. Solid staging, while sturdier makes it easier for mealy bugs and other pests to gain access to plants. Slatted staging lets the air circulate, but pests can still move over it fairly easily. Slatted staging is unsuitable for use with capilliary matting or gravel.

There are several methods for heating greenhouses and cold frames during the winter. Electric fan heaters work well, but are expensive. They produce dry heat, so plants require spraying during the winter on sunny days. Tubular electric heaters are available but the plants need air circulation to keep them at their best. If electrical heating is to be used it is worth investigating Economy 7 or similar tariffs. Gas heaters are very successful, but need pipes laid from the house (or heavy cylinders) and installation can be costly. Paraffin heaters work well and are cheap to run, but can produce a paraffin smell, and need to be used carefully to avoid a fire hazard or sooty plants. Under-tray electric heating can be an efficient way of applying a little warmth to your plants, and a variety of commercial heating pads can be obtained from horticultural suppliers for this purpose.

Under-tray electric heating is not a complete answer to cold conditions as the roots receive the most heat and may be damaged. As the plants are warmer, they may need a little water to prevent excessive dessication. However, if water is supplied directly to the pots or via capillary matting, the warmed stage promotes evaporation with condensation in colder parts of the green house. Experienced electricians may be able to make use of ex-equipment fans which are readily available from surplus stores. Check the intended operating voltage, and make sure that you know how to run them safely from your local mains voltage. A small fan strategically placed in the green house promotes air circulation and encourages healthy growth.

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