Greenhouse Construction & Maintenance

The goal of creating a controlled environment starts with choosing the ideal site location, construction materials, orientation, and equipment. Start with a location that provides quality solar gain through the winter into spring growing season. Orient a stand-alone structure facing east to west with the vent opening facing prevailing, western winds. Choose durable construction materials for the roof, sidewalls, and endwalls that will withstand heavy snow, strong wind, and provide insulation through winter-spring.

Our Main Greenhouse roofing is a 6ml, four-year, double-layer, horticultural grade, polyethylene with an inlet fan to provide airspace for insulation between the two layers. A Stuppy Greenhouse Manufacturing “kit” that includes easy-to-install extrusions to attach the poly to the structure and at the ends.

The sidewalls are 4′ panels of twin-wall, polycarbonate leading to 4′, double wall, insulated, plywood sheets to perimeter concrete footing. Endwalls are full sheets of same polycarbonate. The west end has a temperature activated outside vent with cooling pads inside. The two exhaust fans located on the east end, pull fresh, cool air across the greenhouse and vent it out. We have 2 propane heaters, one overhead and one under the bench with a convection tube, 2 exhaust fans, 4 airflow fans, an environmental controller that co-ordinates the heating and cooling equipment, and a ‘Dozatron’ chemigation system to apply fertilizer and chemicals through the waterline. Ideally, the greenhouse is kept cool and dry. Daytime temperatures through the winter months are in the low seventies and kept above freezing at night.

As the growing season approaches, February 1st in the main greenhouse, nighttime temperatures are increased to 50 while daytime temps stay in the low seventies. In March, the temperature (starting 20 minutes before dawn and for 30 minutes afterwards) is decreased by 8 degrees. This allows for plant height control producing a stockier plant without plant growth regulators/chemicals. This also results in venting excess humidity that accumulates in the greenhouse overnight. Humidity levels through spring are at a comfortable 40% during the day, but increase to 85% at night. Early morning venting can bring that number down to 65% in a matter of minutes reducing the need for chemical application of fungicides. Another way to reduce high, nighttime humidity levels is to finish watering in the greenhouse early and avoid watering on cloudy days.

The Southern Greenhouse roofing is the same as the main greenhouse except it’s a 5ml, two-year, double-layer film. Sidewalls on both sides are manually operated, rollup curtains, and the endwalls are fiberglass. This is also a Stuppy Greenhouse “kit”. Daytime temps are kept in the sixties through the day and just above freezing at night with a thermostatically controlled heater and a shutter/exhaust fan cooling system.

By the end of March, the perennials growing in the southern greenhouse are moved out to the display area benching. Snow and cold temperatures are not unusual in April and we are always ready to drop the Remay fabric to protect our plants.

Tomato seeds are started in the main greenhouse in mid-March. We grow several varieties every season with about 200 seeds per seeding tray. This puts our “starts” ready by mid-May to begin the acclimating process for late May planting. Otherwise, our annuals and perennials are grown from rooted cuttings, seedling liners, and bareroot stock brought in from large growers that specialize in growing for smaller greenhouses, just like us.

Fertilizer rates: 200ppm for actively growing starts and 100ppm once mature. Phosphoric acid is applied at 1oz per 100 gallons of water to achieve a pH of 6.1; without the pH adjustment, our well-water is at 7.9, making nutrients unavailable.

Weeds growing in the gravel are controlled by spraying a mixture that includes: 1 gallon vinegar, ½ cup of salt, and 4 T dishsoap. Hint: Dissolve salt in warm vinegar first.

By early June, temperatures are uncomfortably high in the southern greenhouse, so the poly is pulled, stored, and replaced with a 45% shade cloth. Likewise, shade cloth is pulled over the stay-in-place poly for the main greenhouse by late June.

Pesticide applications: The EPA has defined reduced-risk pesticides as compounds that pose a lower health risk to humans, the environment, and beneficials. These products do not work on the insect’s nervous system like standard insecticides and are therefore more worker-friendly within closed greenhouse environments. We have chosen to use these reduced risk pesticides in our greenhouses including ‘Endeavor’ to control aphids, ‘Conserve’ to control thrips, and Bt (Bacillus thuringiensis) to control shore flies and fungus gnat larvae. Lots of folks fight fungus gnats in their houseplants too and this product works great to control them, naturally.

Growing your own plants can be challenging, but also very satisfying. We hope this information provides you with some insight on how our small operation began in 1991 and some ideas if you are considering building your own greenhouse.

Contributed by Marvel Clyde; Owner, Colorscapes Greenhouse