Everyone with space available should have a greenhouse for three reasons: economy, security and beauty. You can save money by growing some of your own plants from seed, see that the tropical container plants you invested in will survive the winter, and enjoy the beauty of all you grow year round. The definition of greenhouse is ‘an enclosed structure used for the cultivation, protection, and/or exhibition of plants.’ Each one is different and reflects the growing desires of its owner, but the same three factors determine their success: sunlight, orientation, and seal. Water supply, humidity and ventilation, shade, and features such as mist chambers for rooting can be added after construction if need be. The ‘big 3’ factors cannot.
Greenhouses are known as full sun structures, but in our climate, a deciduous tree on the south or west side can provide timely shade in late spring and summer. With such protection, you can naturally extend your greenhouse gardening season. Shade cloth on top of the greenhouse works very well, especially if you want to spend any time in the greenhouse in summer.
Place the greenhouse for maximum winter sun exposure. Be sure the long side of the structure faces east, where the sun comes up. If you choose a lean-to greenhouse or build a sunroom, orient it to the east to avoid heat build-up that can overwork cooling systems.
The difference between a greenhouse and a plastic tent is simply that the greenhouse is carefully sealed. Get the seal tight and the clear surface will amplify the effect of sunlight that passes through it and allow heat to build inside the structure. Glass is the gold standard in greenhouses, but a tightly sealed plastic house works much better than a leaky glass one. Every connecting surface needs to be caulked, taped, or otherwise seamed tight. Your goal is to prevent leaks to the outside and cold spots inside the greenhouse.
Ride around in the South and you will see greenhouses that are a testimony to the ingenuity of the gardeners. An old swing set frame or clothesline poles are covered in plastic to start seeds. They don’t need a door, but instead lift the entire wall for daily ventilation. Recycled materials abound, from sliding glass doors set into a frame to a rooting house made of windows taken from a house undergoing renovation.
Too many people believe a greenhouse will be very expensive to heat, but think of the savings in plants! Use good quality materials, follow the three principles of sun, orientation and sealing tight and heating the greenhouse will not break the bank. Surveys of people who add water features and greenhouses to their home landscapes reveal that size matters. It turns out that their main complaint is that their new addition is too small. An economical greenhouse is one covered with rigid plastic made for outdoor conditions with structural integrity that supports useful additions like roof and fan vents.
Freestanding greenhouses depend on their design strength and construction to keep them on the ground in case of wind lift, but it is not always necessary to pour a complete foundation. A-frame greenhouses handle snow load, but they get the rain off equally well and it is very easy to install shade cloths on their sides. Gable and barn-styles can include removable lower skirts or screen panels to help with air flow. My own Quonset greenhouse is built of pipe hoops set individually in concrete and joined with pipe straps to a 2x4 base board. The ends are framed with more 2x4s surrounding the doors. When Katrina blew the plastic apart, the contents were scattered over an acre. The greenhouse stood strong and was soon recovered.
If you have ever considered a greenhouse, now’s the time to act. Think of what you like to grow and begin to create your own personal greenhouse retreat. A mist system makes it a tropical rainforest and gives you a perfect environment to root many plants. Or you can maintain a dry space perfect for succulents and cacti; your private ‘desert’ will bloom all winter. Container gardeners will love greenhouse gardening because of the control it gives you over their environment. Build a greenhouse to keep your plants happy all winter and it will keep you happy, too.