If you plan on growing all of your vegetables year round, you're going to need a large greenhouse set-up that allows you to control the temperature, light and humidity. On the other hand, if you're just looking to extend your growing season by a few weeks, you can easily get by with a much less complicated system. Before planning your greenhouse, ask yourself what you want to grow in it and how much space you'll really need.
Permanent greenhouse structures are available in many sizes and shapes, ranging from lean-tos and window attachments to small, freestanding patio-sized units and units that can be mounted onto walls. During your planning phase, keep in mind that freestanding units will be the easiest to expand, but if you need utility and water hook-ups they'll be a lot more costly to install. Lean-tos are attached to already existing walls of buildings. This saves the cost of building one less wall and also gives you easier access to utilities. The downside of a lean-to greenhouse is that the existing wall can limit light and it will be more difficult to expand in the future.
The optimal site orientation for a greenhouse is on the south or southeast side of a building, tree or other large structure. An area where plants can get all day sun exposure is ideal, but if that isn't possible, an eastern exposure is a good second choice. Exposure to morning sun is the most important because if a plant's biological processes can get jump started early in the morning, it has the rest of the day to optimize growth.
To avoid the expense of installing a supplemental drainage system, plan to site your greenhouse on high ground. This will make is easy for water and irrigation systems to drain freely away from the site.
There are advantages and disadvantages to all types of greenhouse framing materials. Wood is easy to work with, but even when using rot-resistant wood like cedar, over time it will succumb to the elements and have to be replaced. Wood is not as good as metal at transferring heat, however, which is an advantage if you're planning a greenhouse without a mechanical heating system. Scrap or reclaimed lumber is also readily available. For the budget minded, plastic ribs or PVC make flexible, lightweight supports that are both durable and inexpensive. They work especially well for smaller, freestanding units.
Not only is a dirt floor inexpensive, but it's the best option environmentally. Use a high-quality soil that drains well to make a floor. By covering it with a layer of landscaping stone or gravel you will prevent things from getting muddy. When you need to raise the humidity, simply spray the floor down with water.
Gardener's have many options when it comes to glazing (coverings) for greenhouses. It's best to try and evaluate them by cost, durability and their ability to transmit light. Polyetheylene and other plastics make the least expensive glazing materials. Look for the newer, thicker plastic films though, or you'll be replacing them every year. The thicker films stand up better against the elements, but they will also eventually tear from wind damage or be degraded by the sun. Re-use centers often sell inexpensive windows from deconstruction projects. These can be easily fitted onto a wooden greenhouse frame and also be worked into the ventilation plan.
The amount of heat your greenhouse needs depends entirely on your climate and what you plan to grow in it. If sited properly, your greenhouse will act an effective solar collector and need very little, if any, additional heat. If your climate is very hot, you may want to consider building your greenhouse next to a tree or building to provide it with some afternoon shade.
To ward off the cold, cooler climates can use insulated panels or blankets during the coldest periods. Water can also be used to collect and store heat. Paint metal drums or troughs black to absorb maximum heat. By placing boards over the tops of them, you'll have instant heated shelving for your plants. Electric heating cables can also be laid across benches. These work well for keeping the soil in your pots warm, but won't add to the overall temperature inside the greenhouse.
Create a circulating flow of air by leaving openings for ventilation near the floor and creating an outlet for air near the peak in the roof.
Garden magazines are a good place to look for free plans, and there are hundreds of great links to free greenhouse plans on the web. Here are three:
By Ellen Brown
Doreen from Pine Plains, NY
There are several things to consider when setting up a shelving system for your greenhouse. First, greenhouses are moist environments, so look for shelving made from a material that will hold up to the constant humidity without rusting or rotting. Next, unless you plan to supplement available natural light with artificial lights, look for open shelving that allows light to penetrate through to the shelves beneath it. Finally, make sure the shelving you choose can hold up to the weight of lots of pots filled with plants and moist soil. Other things to consider are size, ease of cleaning, portability, and of course most importantly, your budget.
Sam's Club features a shelving system made out of commercial grade chrome steel for around $75 (plus shipping if you don't have one nearby). The systems features 6 adjustable wire shelves, each rated for up to 600lbs. As an added bonus, the whole system is on casters, which makes moving and cleaning it more convenient, and if you decide to add grow lights to any of the shelves, the fact that they are open will make them easy to hang. If these fit your size and are within your budget, they seem like a great deal to me.
Target also feature similar shelving units in various sizes. I suspect you could find similar units at most of the larger retail discount stores and home centers.
Depending on how your greenhouse has been constructed, another option is to use the wall-mounted closet shelving designed for organizing closets. This is easy to find at any major home or garden center. It allows you to customize your shelving and add to it as your budget allows. The shelves are open and usually coated with plastic. Because they are designed to accommodate hangers, they are ready made for hanging pots. Plan to reinforce them with extra brackets to account for the added weight of heavy pots.
Other ideas include browsing building salvage companies and area thrift stores like Goodwill. You never know when you are going to stumble upon an old bookcase or other piece of furniture that can be converted into shelving.
If you are willing to be creative, consider taking out an ad in a local mid-week or hanging up flyers. People who are spring cleaning their house or garage may be more than happy to unload their "junk" for free (or for trade) as long as you're willing to pick it up. For cheap reclaimed building supplies, don't forget to check out your local materials exchange:
If I can only go 10 feet wide on my greenhouse, can I use the same lenghts of PVC in your 14 foot wide plan and just obtain a higher arc or will the stress on the PVC be too great?
I want to start my vegetable plants for the spring indoors now, then transplant them in 8-10 weeks outdoors. I need suggestions on how I can build a frugal greenhouse in the garage. The only thing is the garage has no heat. I don't know how to add that to the installation. Any help would be appreciated. Thanks.
Hardiness Zone: 7a
By Michael from Knoxville, TN
Yes a little electric space heater does the trick! I use one of those electric oil heaters and it works perfectly! I also keep a fan (the ones you can clip on anywhere) going for air circulation. We replaced the windows in our house last year, as did our neighbor. All of the old windows were saved and went into building my new greenhouse! Have fun!