A greenhouse provides a key element for your garden if you want to maximize your summer yield or diversify your current plant varieties. It offers a nurturing environment to young or delicate plants by offering optimum growing conditions. Your plants will be protected at their most vulnerable stage from harsh environmental conditions like heavy rain, wind, cold and exposure to disease. This helps ensure a strong, healthy, and productive start for the life cycle of your plants.
The biggest advantage of a basic greenhouse is its ability to capture solar radiation and concentrate warmth to facilitate an earlier indoor growth period before the cooler spring conditions outside have stabilized. Vegetable and annual seeds can be germinated in the spring. Outdoor plants can be brought inside to extend their season into the fall, since, at this time, the glass retains the heat that has been stored and emitted by the soil and brickwork within the structure throughout the spring and summer. Just imagine being able to maintain a full, colourful and productive indoor garden all year round.
Evidence of the first greenhouses appeared back in the 15th century Roman times, where the concept of a transparent envelope was constructed using spit laminates of mineral rich stone. Innovations in plate glass production and window frame leading in the 1600's lead to some of the first lean-to style plant conservatories. Equipped with stove heating, delicate plants could be cared for through the winter months.
The 1800s saw advancements in iron framing and helped establish some of the first free-standing structures for nursery applications. Although most greenhouses were custom made, some designs went into commercial production. Some of the more popular plant varieties to become cultivated at this time were chrysanthemums, carnations, roses, and tomatoes.
After World War II, technological advancements improved, once again, bringing today's more common structural materials such as galvanized steel, aluminum, and plastic.
Choosing a Greenhouse
There are many styles of greenhouses to suit a variety of needs, budgets, and space limitations. Many of the different types are variations of two basic structures: the even-span roof and the lean-to.
The even-span greenhouse is the most common choice for larger plant volumes. There are a large variety of structures available in this form. Depending on the individual features, the shape usually offers a good balance between cost, solar exposure, and ventilation.
The circular greenhouse offers the most solar exposure with the least amount of reflection. It also lends itself to some attractive options with respect to plant presentation and appearance. They are relatively more expensive, though, and may not make efficient use of space.
The lean-to is often the smallest and cheapest of the three options. They can be purchased or easily custom built. The lean-to is often constructed as an addition to the side of a house. The advantages here are several: it is visually less obtrusive to your garden, it is easy to supply with electricity because of its close proximity to the home electrical box, it is similarly easy to install plumbing in it, it shares some of the radiant heat from the structure of the house, and it promotes an atrium-like environment for plants that is more accessible when the weather is poor.
Considerations for the appropriateness of each structure depend on the following factors. Sloped windows are essential to capture and not directly reflect the incoming light rays. Sloped roofs can restrict the layout of plants by placing height restrictions on perimeter bench layouts. Greenhouses with full glass walls allow for the most light to enter but have poorer insulating qualities. They are ideal, however, for providing maximum solar exposure to all areas of the interior space including those below benches.
Functionality and Climate
If your greenhouse is a simple weather-dependent structure, flexibility is restricted and the level of required maintenance increased. With the addition of a few basic accessories, your greenhouse can become completely self-sufficient.
The most basic greenhouse can be modulated through its bench design. Cedar benches are common for their natural resistance to heat and water. Multi-tiered benches are often staggered in a way that offers good watering access, flexibility for plants of different heights, and areas of high and low light for different plant requirements.
Ventilation is essential to provide air circulation for your plants. It allows the hot air to escape and balances the level of humidity to prevent problems with mildew. The easiest option is to install an automated skylight that uses a temperature sensitive hydraulic arm which automatically opens to release excessive heat. Similarly, louvered inlet windows at a lower level will contribute to airflow.
In midsummer, the amount of light can be overwhelming. It may therefore be necessary to install some form of window shading. Installing white translucent drapery on the inside of the windows can filter excessive light. This is a flexible solution that can be put up or taken down when needed. Another way is to paint a translucent film on the exterior of the windows with a roller.
Depending on your growing region or plant requirements, a scorching summer may require the installation of full-time translucent polyethylene window panels. When light conditions are low in the winter and early spring, additional lighting can be added to extend daylight hours. A fluorescent fixture makes for a cost-effective option.
A thermostat-controlled heater is another device to help regulate temperatures in the off-season. This can help start plants indoors while the threat of frost still looms outside. It also helps you prolong your greenhouse garden over the cold winter months. Mounted near the base of the structure, the heater usually has a fan to help circulate the warm air throughout the room.
The following is a general calendar of events outlining some simple planting options.
September (before the first frost):
· Lift quality plants from the garden to indoor pots for spring cuttings (geraniums, marguerites, wax begonias, impatiens)
· Take plant cuttings of the above for fall propagation
· Take softwood cuttings (hydrangeas, fuchsias)
· Plant perennial seeds early to allow time for maturity
· Plant salad greens year round, depending on heat (lettuce, cucumbers, tomatoes)
· Collect seeds for spring planting
· Pre-start begonia bulbs and dahlia tubers in pots for early summer flowers
· Start tiny annual seeds that take a long time to establish (tomatoes, impatiens, ageratum, petunias)
· Other medium seeds can be started (marigold, nasturtium, cucumber, peppers)
· Start feeding cuttings and other wintering stock with fertilizer to stimulate foliage
· Young seedlings need root-stimulating food
· Prune oversized plants to maintain a compact shape