Maximum Yield USA August/September 2019 | Page 32

Plastic films can be made of polyethylene (PE), polyvinyl chloride (PVC), and copolymers of these materials. Polyethylene will last one to three years, while PVC and copolymers with UV inhibitors will last longer. Heating and Cooling To control the temperature in your greenhouse, you’ll need to install heating and cooling systems. For most plants, night temperatures of 55-65˚F and a maximum daytime temperature of 85˚F will do. If you simply want to protect your plants from frost, then setting your thermostat to 40˚F will be adequate. Remember to account for the microclimates within your greenhouse. The spaces near walls, the floor, ventilation, and any kind of opening will be cooler than the rest of the area. To heat your greenhouse, you can use a space heater, hot-water or steam system, electric heater, forced-air heater, or radiant heat lamps above plants. A space heater with a few circulating fans is an inexpensive option for smaller greenhouses. Arguably the most efficient system for small greenhouses is a forced-air furnace that distributes heat through ducting or a plastic tube system. The tube is placed as high as possible down the length of the greenhouse to distribute heat evenly so there are no cold spots. To cool your greenhouse, you can use evaporative cooling systems, fogging and misting systems, or shade cloth. Evaporative cooling and fogging systems both increase humidity and work well in drier climates. If your humidity gets higher than 90 per cent, your plants will start having issues and you should bring in a dehumidifier to bring humidity back down between 70 and 85 per cent. Evaporative cooling systems, also known as swamp coolers, pass hot air though a soaked screen or spray of water to cool it down. Foggers and misters work well, however, can be high maintenance when emitters clog. Shading your greenhouse will also bring the temperature down. Trees planted on the south side will offer afternoon shade. You can also use a shade cloth, roll up screen, or paint a compound directly on the glass. Greenhouse Ventilation Proper ventilation is essential in your greenhouse. It circulates the air and keeps the temperature even. It also exchanges the stale air for fresh air and replenishes CO 2 . Vents, intake and exhaust fans, and oscillating fans will create enough air flow for a healthy environment. Without air flow, warm air would rise to the top of the greenhouse and cool air would settle at the bottom. By placing fans in diagonally opposite corners, you will move air in a circular motion and keep temperatures uniform throughout the greenhouse. Intake and exhaust fans work together to exchange stale air for fresh air. The fans you choose should be powerful enough to change the air about once per minute. Vents are helpful when moving air. When the warm air rises and escapes through the roof vent, cool air will be drawn in through the side vents. "Automate everything. If you don’t, you will be tied to your greenhouse, opening and closing vents throughout the day and hand watering all of your plants daily. " Automation Now that you have all the pieces in place, do yourself a favor and automate everything. If you don’t, you will be tied to your greenhouse, opening and closing vents throughout the day and hand watering all of your plants daily. The more money you invest in automation technology, the easier your life will be. You can hook your heaters, cooling system, fans, and vents up to a thermostat that will turn them off and on depending on the temperature. Humidistats will regulate humidifiers and dehumidifiers to keep your humidity levels in check. Automatic watering systems will ensure your plants never get too thirsty. “REMEMBER TO ACCOUNT FOR THE MICROCLIMATES WITHIN YOUR greenhouse.” 32 Maximum Yield A greenhouse is a wonderful addition to any garden. Though it can be costly up front, once it is set up and automated it will extend your growing season, give you space to propagate, and allow you to grow tropical plants you may not have been able to grow otherwise.