In many sections of the country heat is the most expensive item in greenhouse operation; in other areas it is negligible.



Any manufacturer who specializes in greenhouse building will give you accurate estimates of heating costs for your location and greenhouse during an average season. Or a local plumber may advise you.

A friend in Michigan who uses a forced-air circulating heater for her seven-section redwood house finds the cost about $35.00 per season to maintain 50-degree temperatures at night and 60 during the day. A Minnesota grower, employing hot water for the same sized house, keeps it at 65 at night, 75 in the day, at an estimated cost of $105.00 per season.

Ventilation

Your plants should reach the market in tip-top shape, which will not happen if your greenhouse is too cold, too warm, or too drafty. So you should pay close attention to ventilation. Automatically controlled (thermostat) ventilators are helpful and relieve you of constant attention.

If you don't have them, open the ventilators first thing in the morning if the day is due to be hot?regardless of the calendar. During the summer, I leave the ventilators open all the time. In spring and fall, take care that cold drafts do not blow directly over plants. The best way to ration fresh air is to open the ventilators a crack at a time, thus avoiding sharp declines in the inside temperature.

Ridge or side ventilators, and exhaust fans are available for greenhouses. If you are using side vents, be sure that they are arranged in a way that will not cause the air to blow directly across your plants. Louvered side vents provide excellent service and can function as part of the summer cooling system you may eventually wish to install. Plants such as cymbidium and cyclamen require rather low temperatures part of the year another good reason for a cooling system.

The large commercial grower in a huge greenhouse?with his constant personal attention, abundant water supply, and great body of air overhead?can well afford to have an opening in the roof as a means of ventilation.

But not so the person with a typically small, low-roofed, hobby greenhouse. Too much air can escape in a short time. And it is not only the hot air that escapes through a roof vent; with it goes the humidity the plants need so very much.

Automatic ventilation, via a fan system, changes the air completely every 3 minutes. With the fan in operation only briefly, your plants benefit from whatever humidity is in the greenhouse.

You can purchase manual ventilator openers made of metal, or by investing a little more, you can install automatic openers. These are hooked up to thermostats and will open and shut ventilators whenever a change of air is advisable.

Humidification and Cooling

Evaporative coolers do a wonderful job of both humidifying and cooling. One unit offers controlled cooling and humidifying?from a gentle breeze to a full torrent of air at the turn of a three-speed motor switch.

At full capacity this unit will change the air in a 14- by 30-foot greenhouse approximately every 2 minutes. Directional air-flow louvers on the fan swing easily into position to control flow to any part of the house to promote draft-free ventilation, cooling, and humidifying.

Most coolers currently on the market are built for eye appeal, as well as service and stability. In one model, heavy-gauge zinc-coated steel cabinets and louvers are primed with rust-resisting zinc chromate and finished in baked-on enamel, while special non-vibrating mountings support the heavy three-speed motor. Evaporating elements are constructed of three removable pads of odourless aspen.