Whether you decide to build or buy a greenhouse, I hope I can save you the trial and error and frustration I experienced building and operating a greenhouse.

Will this be your last one?” I heard my sister-in-law, Marcy, say behind me as I stood in my newly-built greenhouse. After several years of trial and error, I think I have indeed built my last greenhouse—one that should stand the test of time.

My first attempt at a small greenhouse, or “grow house,” literally blew over in a good nor’easter. The second one I assembled in a wind-protected area up against my home. It served me well until it died of old age, the poly plastic fading and finally tearing and pulling away from the plastic battens.

Next was a quonset-style greenhouse made of wood and PVC electrical conduit. This hoop-style house served me well for a few years, but each year the weight of the snow caused the plastic bows to bend and buckle until I could hardly stand up straight.

A few summers ago, I was smitten by a greenhouse I saw in nearby Dafter, not far from the Cloverland Electric Cooperative office. These folks were nice enough to let me take some photos and measurements of the structure, which is made out of wood with a polycarbonate covering.

The house I built is 16×10 feet, with a polywoven plastic covering. The polyweave appears to be stronger than regular polyethylene plastic, and the house has a peaked roof that easily sheds the snow without any help from me. It is also very roomy and feels, well, like home.

Of course, your decision to buy or build your own greenhouse will depend on your own needs, wants and budget.

Size And Purpose
For the greenhouse hobbyist, a house about the size of mine is adequate to grow at least 50 flats of plants and a dozen hanging baskets. Larger greenhouses are for those who plan on selling flowers or produce. Sizes range from 24×48 to 30×90 feet. These should be of metal construction with a poly plastic or polycarbonate covering. The basic framework for these greenhouses starts at $7,000.

Polyplastic, sold under the trade name Tufflite, is the cheapest covering for a greenhouse. However, it must be replaced in three to four years. For my small house, I purchased a woven poly from a small supplier in North Dakota. It was not only easier to work with than the clear poly plastic, but I’m counting on it lasting longer.

Polycarbonate is much more expensive than the woven and the clear, but lasts much longer. The covering for a 30×90-foot greenhouse runs over $11,000, but comes with a 30-year warranty. It would cost about $1,000 to cover my small house with polycarbonate. Polycarbonate panels also have a bit of an insulating factor, which can save on energy costs.

Inside The Greenhouse
The price of a greenhouse can be misleading if you don’t consider the cost of heaters, fans, tables, hoses, flooring, and assorted tools and gadgets. The heater is the major expense. These heaters are usually fan-forced and run on gas and/or fan-forced hot water. Heaters start at about $500.

Just as heat is important in a greenhouse, so is the ability to cool down a house, especially on sunny days. Automatic built-in and free-standing oscillating fans not only cool down a greenhouse, but provide air circulation around plants, which helps prevent disease.

Managing a Greenhouse
Five factors affect the growth of plants in a greenhouse: light, temperature, growing medium, humidity and heat.

Greenhouses should be situated, if possible, with an east/west orientation. This will allow a long south-facing span for your sun-loving plants. Try to maintain daytime temperatures at 65-70 degrees, 10 degrees cooler at night. Plants don’t like huge fluctuations in temperatures. Coordinate your fans and heaters to maintain consistent temperatures throughout the day.

Whatever you do, don’t bring garden soil into a greenhouse! This not only encourages disease, but the soil, when placed in containers, becomes too heavy for growing tiny seedlings. A good soil-less mix for containers will contain perlite, vermiculite and peat moss. These are sold under different trade names, including Pro-mix and Baccto.

Humid plants are happy plants. Ideal humidity levels in a greenhouse run between 50 and 60 percent. Humidity levels are controlled by proper ventilation.