How To Prepare Your Greenhouse Site
by Damien Andrews
Today, more and more people are making the decision that a greenhouse would make a fine addition to their yard. This decision is attributable to several factors in today's world including the rapidly rising cost of foods; the desire to eliminate the intake of industrial preservatives; the desire to eliminate the intake of pesticides used commercially; and the desire to eliminate the ingestion of commercial herbicides. Many people decide to install a greenhouse simply because they are aware of how much better homegrown vegetables and spices taste. One very nice reason to have a greenhouse is often overlooked. Having a greenhouse will extend the growing season for a garden. Seeds can be started early and then easily transplanted in peat pots to the garden.
Before you get around to preparing your greenhouse site, you'll want to determine the size of the greenhouse that's best suited to your needs and wishes. Practically every size and configuration of prefabricated greenhouse is available. You can select from round, square, rectangle, and lean-to styles. The most common greenhouse frames are made from cedar, redwood and aluminum. The most common greenhouse glazing (glazing in a greenhouse refers to the areas the light will pass through) materials are polycarbonates and fiberglass.
Once you decide on the size and shape of your new greenhouse, you'll select the location where you want to install it. When selecting your location, be sure to take into account proper orientation to the sun. You won't want any shade covering the greenhouse, and you'll want to orient the shorter sides to the east and west. Some people prefer installing rectangular shaped greenhouses with the long side facing 'solar south' or 'due south.' This is a matter of personal preference, as well as any limitations presented by the site you've selected for your greenhouse.
Once you decide the size and location of the greenhouse that's right for you, it's time to start preparing your greenhouse site for installation of the new greenhouse. This is a relatively straightforward process with a few unique considerations to bear in mind.
• Mark off the area where you'll be preparing your greenhouse site. If you've selected a square or rectangular greenhouse, be sure to compute the hypotenuse so that your new greenhouse site is perfectly squared (has 90° corners). Use stakes and strong nylon string to mark off your greenhouse site. The diagram below shows the walls and hypotenuse for a greenhouse that is 10' x 5' in size.
• Remove any gravel, rocks, sod and debris from the greenhouse site. Be sure you know where underground electrical and plumbing, including automatic watering system components, are located before doing any digging!
• Level your greenhouse site. If your selected greenhouse site is on a slope, you may require some small earth moving equipment for this stage. If you raise a level with fresh dirt, be sure to compact it appropriately before you proceed to the next step. The earth you are leveling does not have to be perfectly level as it will not be the actual foundation for your greenhouse frame, but it should be relatively close to level. NOTE: the grade of your leveling should allow for the addition of 4" of gravel so that it will not allow gravel to touch the inside walls of the greenhouse when it is placed onto the foundation. The diagram below shows an example of the proper grades, but the depth you level to will depend on the intended height of the foundation/footings.
• Install a 4" PVC pipe that runs from inside the greenhouse site to outside the staked area. This pipe will allow you to easily run water or electrical lines into the greenhouse after it is installed on the site. Use black 4" PVC – usually used for sewer lines – as it will cost less than white PVC will. Stub up and temporarily seal the ends of the installed pipe for easy access later, and to prevent debris from filling the pipe. Duct tape seals stubs quite effectively. The stub inside the greenhouse site should be close to a wall, so as to minimize space use. See the diagram below.
• Cover the entire greenhouse site with the black nylon that is designed to prevent the growth of vegetation. Be sure to overlap the nylon, which comes in varying size rolls, adequately so there are no spaces between strips. This will prevent weeds and grasses from growing up through your greenhouse floor. This step costs a few extra dollars and takes a little while, but it will save you countless hours over the years.
• Now is the time to install the foundation upon which your greenhouse walls will sit. Since a greenhouse is so light, you have many options to choose from. Some people even lay down treated 4" x 4" lumber, anchor it to the ground and then attach their greenhouse walls to it. Others pour a concrete footing and others use one of the types of post and pier systems available. The choice is yours, but it is highly suggested that the top of the foundation you install be wood so that you can easily attach the greenhouse base to it. If you use a concrete foundation, have your contractor install foundation bolts that you can then easily attach 2" x 6" (or any more appropriately sized) treated lumber to.
• Install and spread 4" of gravel inside the finished foundation. Gravel that is sized between 5/8" and 1" is ideal. If desired, a wooden slatted floor can be constructed atop this gravel, but the gravel itself makes a dandy floor for a greenhouse. The diagram below shows a rough of the prepared your greenhouse site.
You have now finished preparing your greenhouse site for the installation of your new greenhouse. Best of luck to you in all of your growing adventures!