Greenhouses and growing structures Horticulture 2

Greenhouse A building characterized by the roof and walls made largely of glass or clear plastics, that provides an environment for plant growth. A range of greenhouse is just a group of greenhouse that are placed in one location

Greenhouses come in a variety of styles. 1.Even span

2. Quonset

3. Gothic

4. Lean-to

5. Contiguous

6. Ridge and furrow

Greenhouse coverings: Glass- in the past, glass was the covering of choice. It was somewhat durable, and let in a high percentage of light.

However, glass can be easily broken, and does become brittle with age. Another choice was rigid plastics, like fiber glass. These panels have durability, and are inexpensive. Light transmition is good, but not as good as glass panels. Sun can cause fiberglass to yellow and chip. It is also quite flammable.

Currently, the greenhouse covering most often used is polycarbonate. Polycarbonates, sometime known by the commercial name, Lexan, is widely used in variety of applications. For greenhouses, it is know for good light transmition, strength, and even can be insulated to prevent heat loss.

The last covering commonly found is poly plastic. Polyethylene plastic is a durable soft plastic. It is commonly used on temporary greenhouses, or seasonal cold frames. Although it can be effective, sun can cause deterioration of poly greenhouse skins in just a few months. So, it is inexpensive, but must be replaced frequently.

Polyethylene covering on a hobby greenhouse.

Greenhouse frames, or the skeleton of the greenhouse come in many materials. Wood- the least expensive and the easiest to find. Redwood or cedar has the best durability, and lumber must not be chemically treated. Wood frames tend to rot, warp, and decay. To prevent these problems, wooden frames should be painted, usually white for light reflection. Painting must occur on a regular maintenance schedule.

This is an example of a wooden frame greenhouse.

Wood and steel frames- This framing system is not as popular as it once was. The combination of wood and steel was considered durable, but required frequent maintenance, like painting. It is considered more durable than the all wood house, but as mentioned, does require work.

An example of a wooden and steel frame.

Aluminum frames Most greenhouses constructed at this time have aluminum frames. It is durable, light weight, but strong. It doesn’t require painting. It can be expensive.

Aluminum frame greenhouse.

Heating, cooling and ventilation of greenhouses. Heating, cooling, and ventilation of a greenhouse is essential for good plant growth. Without adequate air movement, and cooling systems plants will not flourish, and disease could follow. In many parts of the country, heating systems must be able to keep the greenhouse warm in even the coldest temperatures.

Heating systems include : Hot water heat. Hot water is circulated through pipes heating the air in the greenhouse. These pipes are commonly finned, allowing for more heated surface area, and better heat distribution.

Steam heat is another heating system found in greenhouses.

One of the most common is forced hot air. These units are hung from the ceiling of the greenhouse. Sometimes, the greenhouse uses convection tubes to evenly distribute the heated air.

Greenhouse cooling: this can be done in many ways. One of the most common is Fan and Pad. Pads are moistened by water, and the fan behind them cools the air that is blowing into the greenhouse.

Greenhouses can also be cooled by evaporative coolers. Water moves over the fan, and blown into the greenhouse.

To keep the greenhouse cooler in the warm spring or hot summer months, shading clothes are often used. These can be placed on the interior or exterior of the greenhouse. This fabric is made of plastic, and the grower can choose the amount of shading required for the crop or the climate. Shading can be done with paint as well.

Ventilation of the greenhouse keeps the air moving and helps keep the temperatures in the greenhouse regulated. One way to ventilate the greenhouse is with roof or side vents. The vents open and close at a set temperature.

Exhaust fans are also used to control air movement. Some fan bring in air, and some fans expel heated air.

In ventilation, convections tubes are also used to allow cool air to move throughout the greenhouse. These clear plastic tubes often run the length of the greenhouse. The fan at one end keeps the tube inflated.

Watering systems: Plants need water, although not every day. Here are some methods that greenhouses can use to get this job done. The first is sub irrigation. Using capillary action, the plants are watered from below. This is beneficial to plants like African violets, with pubescent leaves.

A system similar to the sub irrigation is the system is called the ebb and flow system. Benches are flooded with water, and when watering is completed, the benches are drained.

Another popular greenhouse watering system is the spaghetti or drip system. This system uses small tubes connected to a header. These tubes emit gallons of water per hour. They work well because water is not wasted, it goes where it needs to be. However, it requires more maintenance than other systems.

Spray systems are another way of watering the greenhouse. This systems waters much like a system used to water lawns. It can be easily installed, but some plants do not do well when watered in this manner.

Mist systems are commonly used in greenhouses as well. They are frequently used on seedlings and on newly seeded flats.

Of course, watering can always be done by hand. This method does take time, is sometimes inaccurate. It is inexpensive, and anyone can do it. Done with hose sprayer or cans, it gets the job done.

Lighting is another factor to consider when building a greenhouse. Although sunlight is preferred, supplemental lighting must be used. In the winter, and spring this supplemental lighting helps the plants with photosynthesis. There are 3 main types of lighting a greenhouse. One is high density gas discharge, another is florescence, and the last is incandescent bulbs. This chart shows the comparison between the different types, and the number of bulbs needed for the same amount of light.

Incandescent lighting Incandescent lighting Fluorescent lighting High intensity gas discharge lighting

With additional lighting, greenhouse crops can be very successful, even in winter. With additional lighting, greenhouse crops can be very successful, even in winter.

Now for the interior of the greenhouse. Benches are the tables that plants are placed on. Standard industry size is 4’x8’, but this can vary depending upon the growers needs. Benches can be made of a variety of materials. Small greenhouse may choose wood, or wood and wire mesh, which are inexpensive to make.

Other benches can be made of plastic. This material is durable, easy to keep clean, and will not warp. Plastic benches are available in many sizes, and can be stacked.

Commercial greenhouses often choose metal benches. These benches can be stationary or rolling, giving the grower many options in crop selection. All benches must be sturdy, easily maintained, a comfortable working height, and of course, allow water to easily drain.

The last item to consider is the flooring material. Options include, crushed rock or gravel, concrete slab or blocks, and dirt. What the grower needs to remember is the maintenance of each of these floors. The greenhouse should be a safe place to work, with all tools and equipment stored, and should be kept weed free.

An important part of the greenhouse is the head house. The head house is the workspace for the greenhouse. It should have benches for work, bins for soil, storage for pots, tools, fertilizers, and pesticides.

Additional growing structures include:  Cold frames- The only heat that the cold frame has is from the sun. The cold frame acts as a halfway point for plants that have been growing in the greenhouse and outdoors. At this time, when the plants become hardened to outside wind, temperature, light and water fluctuations, the cold frame is essential.

Shade house or Lath house  The lath house or shade house are primarily used to protect plants from damaging sunlight and temperatures. They resemble pole buildings with a removable covering. They are most commonly found in the southern climates.

Cold frames

Lath house Shade house

Cold storage facilities are important to the horticulture industry. Most fruits, vegetables, and flowers are held in storage before they are sent to market.

Greenhouses are an important part of horticulture.