How To Choose Your Greenhouse

There are many factors to take into consideration when you plan your new greenhouse venture – factors you wouldn’t necessarily think of before you make your purchase. I suggest you first read this section thoroughly, as it may change the unit you ultimately decide is your dream greenhouse.

Placement

One of the first orders of business is choosing the placement of your greenhouse.  If you use a lean-to style, try to place it somewhere where the base is sitting on the ground rather than a solid surface such as a deck.  It will be easier to control the temperature.

If you are using a freestanding structure there will be a several factors to consider.  Think about these carefully as once you have built your greenhouse you’re going to have to live with it unless you want to take it apart and start all over again – not a pleasant thought.

If you use your greenhouse for:

Seedlings and propagation – partial shade is optimal.  If this is not possible, you can use shade cloth.

Growing in cold seasons – maximum sun exposure is the best choice. Southern exposure is best but if this is not possible, you can make up the difference with heaters and lighting although it’s a more expensive solution.    In order, the next preferred orientations are, in order; southeastern, southwestern, eastern, then western.  A northern exposure is too shady for a greenhouse.  An east-west facing greenhouse will get 25% more light than a north-south as it presents more surface to the sun at a right angle.  Rule of thumb – at least 6 hours of sunlight each day.

Keep in mind that the sun is higher in the summer than the winter. A spot that seemed perfect in June may be a problem come January.

Shadows will move as well.  Any shadows cast by any trees or buildings will change throughout the year. Long shadows can mean sun blockage where you need sun the most!  The more accurately you can determine the location of the sun in the sky (and therefore the shadows throughout the year), the more accurate will be your placement.

Location of Door

If possible, place the door of your greenhouse in a direction away from the wind. If your wind typically blows up from the south, face the door north to limit breeze entrance and heat loss.

***Important***

A flat pad on which to place your greenhouse is critical.  If you can make the pad perfectly flat you will reduce stress on the structure’s frame as well as keep air from leaking.

Styles

For a permanent structure, you have different styles to choose from.  The major styles that can be purchased are:
1.    Attached or lean-to
2.    A-frame,
3.    Gothic Arch
4.    Span Roof (Sun Country)

1.   Attached or Lean-To

This type of greenhouse is an extension of the home or other permanent structure. There is usually direct access to the house, water and electricity are easily extended to the structure. In northern climates, an attached greenhouse should not be located under a sloping roof because of icicles and snow slides. Keep in mind that if it’s placed on a wooden deck, expecially a raised deck, a cold draft can come in through the floor boards which will make controlling the temperature inside your lean-to more difficult and more expensive.

2.   A-frame

Simple to construct, the A-frame can be built in sections on the ground and then raised into place and covered. Although the shape is ideal for heavy snow loads, it provides limited head room and is difficult to ventilate. This is not an ideal shape for a permanent structure.

3.   Gothic Arch

The gothic roof line is made from laminated strips over which a permanent covering is installed. This style is a good choice for regions with lots of rain and snow; the pointed top and curved sides keep precipitation from collecting.

4.  Rounded Arch

Similar to the Gothis Arch, this roofline is rounded at the top and also a good choice for regions with a lot of snow.

5.  Span Roof

This freestanding style is a very common and usable shape. The interior layout is extremely practical. In some models there is easy access for a loaded wheelbarrow if the door opening is large. Often there is a door at either end. One variations of the span roof design is the gambrel roof (barn shaped) greenhouse.

6.  Steep Pitch

The optimum 45 degree roof slope transmits low angle sun in the winter and reflects high angle sun in the summer. This increases heat in the winter and reduces it in the summer months. It also leaves lots of headroom and plant hanging space. The steep roof slope sheds snow in the winter and can withstand heavy snow loads.

***Important***

a.  Pay attention to the height of the ridge and the side.  You may have a 10ft peak but if the side panels are too low, you’ll be giving up needed space.  Hanging plants will also become a problem.  Unless you’ve opted for a gothic arch or rounded roofline, your sidewalls should be at a very minimum 5 ft in height.

b.  If you plan to winter plants, a wider greenhouse is best.  To breed plants, a longer more narrow greenhouse will be optimal.

Frame Material

Plastic or PVC

Plastic or PVC greenhouse framing kits are inexpensive and easy to assemble. With a plastic framed greenhouse, you can move your greenhouse easily if the need arises. If you are considering this type of greenhouse kit you will need to take into account how strong winds are in your area. If you live in a high wind area you might not want to use this framing, or at least will need to anchor it down for support. Plastic bends and breaks when under duress from extreme weather, so it is ideal for milder climates. Plastic framed greenhouses are also a good beginner greenhouse.

Aluminum

Aluminum will not rust and can withstand extreme weather. Aluminum framed greenhouses are designed as compatible with a variety of coverings from plastic, to glass, and polycarbonate. The channels in aluminum framing generally include details for you to add accessories to or to hang baskets from. An aluminum framed greenhouse offers ease in assembly for the do-it-yourself gardener.

Wood

Wood is aesthetically pleasing, especially when combined with glass. It has the added bonus of being a natural insulator as it absorbs heat throughout the day and releases it throughout the night. Unfortunately, wood also absorbs moisture in the air, and will rot faster, requiring more treatment/maintenance than any other framing. Therefore it is ideal for very dry climates.

Galvanized Steel

Galvanized steel isn’t used much for hobby greenhouses due to its high cost.  Additionally, the heavy weight will also add to shipping cost.  Some greenhouses use galvanized steel for the base however, for extra strong support.

Panel Material

One of the most important decisions you will make is the choice of material to use in your panels.  You will want a material that will let in the maximum amount of light while allowing the least amount of heat to escape. If you live in an extreme climate, the panels must be strong enough to withstand wind, hail and heavy snow loads. Greenhouse glazing has improved remarkably in recent years. In addition to glass there is a wide range of plastic glazing in the form of film sheeting and rigid panels.

Polycarbonate-Opaque or Clear

One of the most popular panel materials today is polycarbonate.  Polycarbs comes in corrugated or flat sheets of varying thickness. These rigid plastics are shatterproof which is ideal when you have children running through your yard, or if you have rough weather. They are lightweight and easy to cut if you want to run any tubing or wires through the panels. Another advantage of rigid plastics is that they retain heat very well, the thicker the better. And with dualwall polycarbonates, your condensation is lessened to a great degree.

If you purchase a greenhouse with polycarb panels, be sure they have UV protective coating.

Glass

Glass was considered the standard of covering for greenhouses in earlier years. Glass is heavier than many plastics, and requires a sturdy frame. The main problem with glass is the breakability factor. If you live in a high wind area or have plenty of children playing around your greenhouse, you will find yourself replacing glass often. Apart from the prospect of breaking, glass can also become brittle with aging.

Glass has undergone many improvements in recent years. Among the most important is increased strength (double and triple strength ratings) to resist breaking. Larger panes are also available; because fewer structural members are needed, more light can enter the greenhouse.

Other advances have cut down on heat loss. Double-walled tempered glass reduces it by about one third. Low-emissive, or low-E, coating, is another option; it reduces heat loss without a corresponding loss of light. In addition to being energy efficient, low-e glass reduces condensation, partially blocks ultraviolet rays, and makes the inside glass warmer to the touch.

Flooring or Base

Some gardeners like a solid foundation on which to place their greenhouse, but consider this.  If the slab is solid with no drainage, standing water is dangerous.  If you allow the greenhouse to freeze, the slab can become solid ice and very slippery.  On the other hand, if there is standing water you won’t want to be working around electricity.

Other drawbacks of a concrete slab is that it stays too cold in winter and too hot in summer making it more difficult to regulate your interior temperature.

Ideally your greenhouse floor should be free draining.  If you like a solid surface to stand on, consider a path of concrete or flagstone graded slightly toward the edge.  The rest of the floor surface could be gravel which is easy to brush away if you want to plant something directly into the ground.

Before you assemble your greenhouse and after you create a flat pad on which to place your greenhouse, remove all grass and weeds from the area and cover with a weed control mat.

If you place your greenhouse on a wood deck as you might, especially for a lean-to style, cold air can blow in through the cracks in the deck making it more difficult and expensive to heat and control the temperature in your greenhouse.

Take your time – think it through. You’ll be glad you did.

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