It will soon be time to start seeds in my greenhouse. I built the greenhouse from material that I scrounged over several years and finally got around to putting it all together about 10 years ago. I have enjoyed my greenhouse so much that I wish that I had built it much sooner. There is something indescribably relaxing to be with seeds and plants in a cozy, warm, greenhouse when the outside weather is foul.
There are several things to consider when planning and installing a green house. Is there a site on your property that will provide the solar inputs needed for the green house to work? Shading by trees or other buildings is generally undesired and orientation is important. The long axis of the green house should face south and it can be as much as 20 degrees off true south toward the west to optimize solar exposure.
True south is where the sun is at noon so you can use that as a guide or a magnetic compass, but you will need to adjust the compass reading for true north by the declination value for the area. I prefer the sun at noon which is simple to do this time of year. This is also the best time of year to see if there are shade obstructions to your site as the sun is low in the sky and winter and early spring is the time when a greenhouse is most useful.
To what purposes will you use your green house is another consideration. If you only plan to over winter frost-sensitive plants then perhaps you don’t need electricity. However, if you are going to actually use it for starting plants from seeds or cuttings then water and electricity are very important and you will need to consider this in locating the greenhouse. It is also important to have good drainage and, if possible, shelter from wind which can diminish interior heat. My greenhouse is on the south side of a shop building and therefore electricity was easy to access and the building blocks north winds. It is also good to have a wide path to the green house for moving plants, compost, potting materials, etc. to and from the structure with a garden cart or wheel barrow.
I built my shed green house of glass panels. My neighbor had worked at a glass shop and had saved some 2 ft x 6 ft. glass panels for years and generously gave them to me for the roof to get them out of his garage. I also had saved some patio glass doors that I relieved someone of at the dump 25 plus years ago. I used these for the south facing wall. The back of the green house was covered with redwood boards I salvaged from the old tank house that blew over in a 1978 December storm. The frame I made from new 4×4 redwood posts and 2×4’s.
Out-fitting the green house, once built, is the next job. A bench space makes it is easier to work with plants and it runs the length of the greenhouse. It was decked with salvaged redwood fence boards. If you are starting plants from seed—lettuce, tomatoes, peppers, eggplant or flowers—in January or February you will need some heat supplied by heating mats and you will need auxiliary lighting on a timer. Day length is too short for plants at this time of year so I provide about 14 hours of fluorescent lighting to the plants once they have germinated. Otherwise you will end up with leggy, spindly plants that are reaching for more light. I achieve this using a
grow rack with shelves for the heat mats and lights above them and a timer that controls all the lights. I had this setup in a garage, but after I built the greenhouse, I moved the grow rack into my greenhouse. After the plants are growing and day length increases, I transplant them to pots and move them to the bench.
There can be too much heat in a greenhouse. Hence a fan on a thermostat is good at controlling temperatures and a shade cloth may help reduce solar inputs in late winter when the sun is ascendant. Solar powered vents can also reduce temperatures on small greenhouses.
You can buy very nice greenhouses to meet your needs. You can buy them in kit form to be assembled. One very helpful website for planning and building your own greenhouse is: (http://www.charleysgreenhouse.com/index.cfm?page=_tips). It is a matter of your capabilities, budget and what your needs are, but if you are an avid gardener, you will love having a greenhouse.
If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website: http://sjmastergardeners.ucanr.edu/CONTACT_US/