Greenhouse Considerations for Central Oregon

by Ash Baugher of Against The Grain Carpentry

Whether you are an accomplished gardener or an up and coming aspiring one, you know one thing, it is not as easy as they make it look on Pinterest. Especially here in Central Oregon. As beautiful as it is and with all of our sunshine, one may think growing a thick lustrous garden to be no sweat — but that couldn’t be farther from the truth.

We have many challenging factors in our high desert climate, such as scorching hot summer days with very little rain, major dips in temperature when the sun goes down, high winds, not to mention all of the hungry critters that love to munch on those veggies. So the good in all of this is the sunshine, which plants love. If you could only harness the sunshine and control the other elements, then maybe you will have a fighting chance. I’m here to tell you that with a greenhouse it is entirely possible to successfully garden here in Central Oregon.

Your greenhouse might be your ticket to success, but you still have to drive the bus to get there. Just because you have one doesn’t mean successful gardening is in the bag. Your greenhouse has to be set up right for your location and what you want to grow. For example, if you live out east under full sun, you will want to find a location to get a little shade if possible. Or, if you are in a heavily forested area, finding your sunny spot is the name of the game. On the hot summer days, air movement is key because if it is hot outside then it will be hotter in your greenhouse. You want that air inside your greenhouse moving as much as possible and exchanging with the outside air to keep your plants from getting too hot. This can be achieved with some nice opening windows and perhaps a Dutch door, where you can open the top but keep the bottom closed. If you have a larger house you will most likely want some fan power for air movement. Ideally you’ll want the fan positioned as high as possible and blowing out of the house, drawing air in from some intake vents that are down low. The fan can be powered with electric or solar, whichever works better for your situation, but making sure the cfm rating (cubic feet per minute) is greater than the size of your greenhouse. You can also help air movement with oscillating fans placed in the corners.

The challenge on the other end of the spectrum is keeping the temps up at night to keep plants from freezing. Of course heaters are helpful, but there are some simple steps that you can take — like making sure your doors, windows and vents are closed. Other things, such as lower wall sections made of wood with insulation rather than polycarbonate or glass, can help with both cooling during the day and holding heat in during the night.

There are different choices of window options from glass to polycarbonate. We like to use polycarbonate for a few combined reasons. It is easier than glass to cut to size and attach. It is safer, more cost effective and resistant to hail and breakage. It comes in different thickness options, giving it thermal properties. It also has different levels of UV protection, depending on how much sun exposure you have. We recommend a tinted poly on the roof for areas of higher levels of sun exposure. For thermal protection we recommend at least a double walled poly with an air space in between. For thermal gains there are other things that you can do too. Placing things inside the greenhouse that hold heat, such as containers of water or porous rocks which will help absorb heat during the day, helping to keep it cooler and release it back into the air at night, and in-turn helping to warm the space.

Construction is a key factor in your greenhouse, especially in regards to how long you want it to last. A greenhouse properly built out of solid materials can last you a very long time as opposed to the greenhouses that just looks nice and come from kits, but may not hold up through one of our harsh winters. We choose wood for our greenhouses for a few reasons. Lumber is readily available in all different lengths and fairly easy to work with. It is also heavy and builds a strong greenhouse that is not going to budge much under the elements. The common lumber in Oregon is Douglas Fir which is resistant to rot and decay and works great, especially if treated and maintained well. Cedar is a great option too, and is also highly resistant against decay. We generally use Cedar for all of our accents such as siding and doors. We start with kiln dried lumber to avoid shrinking and warping. We always pretreat all of our lumber before assembly allowing for a thorough treatment of all end grain. We also screw all lumber together for a secure connection. A steep roof pitch works well for shedding the elements and keeping the snow load off from your greenhouse. Most of our standard design greenhouses have a steep pitch to enable the elements to shed off nicely. We also use a pressure treated bottom plate for the bottom of the walls to give extra protection for materials contacting the ground.

Last but not least would be your base or foundation. Some folks like to build right on the dirt which is fine if you have a fairly flat and level surface. We generally recommend building a compacted gravel base held together by a pressure treated 4×4 perimeter. The material is usually a mix of 3/4 minus gravel mixed with finer crushed gravel. This will set up nicely to walk on without tripping you up, but most importantly will allow excess water to drain. We also like to place a weed barrier cloth under the gravel to help prevent unwanted weeds from popping up.

There are lots of opinions out there on gardening and greenhouses, and these are just some of the things that have evolved in our process so far.

Thanks and happy gardening!

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