Greenhouses

A cold frame (also known as a hotbed) is a way of growing young plants during the cold end of winter or start of spring, keeping them warm to give them a chance to survive and thrive despite the cold. A cold frame consists of a wooden box with a glass lid that can be opened and closed with ease. The cold frame acts as a mini greenhouse which can be opened to take advantage of the day's heat and closed to keep the warmth in at night.

A cloche, French for "bell", is a miniature greenhouse that can be placed directly over plants.

A DIY cloche can be made from a plastic bottle; alternatively, just the bottom can be cut off and the top pressed into the ground, providing warmth and protection for seedlings. In cold climates this allows seeds to be planted a few weeks earlier. The cap may be used for further control - remove it in warm weather, replace it at nights. A simpler way is to leave it off entirely - this will still offer some protection (though not as much) while needing less attention (and less concern about letting the seedlings overheat by leaving the cap on during a warm day). Further info: An internet search for plastic-bottle miniature-greenhouse yields many relevant hits.

It is possible to build viable greenhouses with only the following construction materials:

• Plastic bottles
• Structural material (timber, brick, etc)
• Wire, or resilient cord
• Fasteners (nails/screws)

Seawater greenhouse is a new form of technology, invented by Charlie Paton that can help to address water scarcity and quality problems. So far this form of technology has only been implemented in a handful of pilot systems around the world and all of these are still currently in progress; however, they show extremely high promise in the areas they have been deployed and give hope for the struggles of the people living in arid lands. Currently, there is no determined limit to the applications or the lifetime of the greenhouses. Thus, seawater greenhouses are not applicable everywhere.

Seawater greenhouses vary a fair amount from the conventional Dutch greenhouses, which is what the public normally associates greenhouses with. The differences though, are pretty astounding as they work in similar, but much more sustainable ways. They can be cheaper than the standard Dutch Greenhouse, they provide free water with no upkeep costs and without running into the carbon dioxide constrictions that Dutch greenhouses typically run into.

There is a special type of solar greenhouse that is common in China but largely unknown in the rest of the world. The concept originated in the 1970s and 80s and has been promoted by the government in China. To maximize solar heat collection, the greenhouse is facing south but has solid walls on its north (back), east and west side. Another feature is that it can be covered with insulating material at night (straw mats, other), which is then rolled up again in the morning. Most of these greenhouses do not require extra heating during the cold season, yet still manage to avoid freezing temperatures. The precise geometric configuration depends on latitude. All sorts of variations exist, from very low-tech, build-it-yourself versions with simple materials (bricks, rammed earth, bamboo, etc.) to very high-tech versions (steel, ventilation). The articles linked below, especially the one from Low-Tech Magazine, have much more information and photos.