The first year I owned my greenhouse, I planted a variety of plants, vegetables, flowers and herbs, in the last days of winter, and was thrilled to see them all growing and thriving in the bright warmth contained inside. However, on the first really warm day near the end of spring, I went out to find most of my plants drooping and spotting and looking anything but healthy! This was not supposed to happen in a greenhouse, I thought! The plants all looked so healthy just the day before, so what was going on?

It took a quick phone call to the company that sold me the greenhouse to realize that I probably should have bought the additional few and inexpensive items needed to properly ventilate and shade a greenhouse.  But in the dead of a Wisconsin winter, I just couldn't imagine wanting to exhaust hot air!

So how do you properly vent a greenhouse? Here's a list of items that are essential after the temperature in your area climbs anywhere above 80 degrees:

•    Roof ventilation panels. These are pretty much standard issue on quality greenhouse kits these days. Just remember to use them once you get into the mid 70-degree sunny weather. Temperatures inside a greenhouse are much hotter than the ambient air outside, but an open roof panel can exhaust the worst of it.

•    Louvers. These are great for being able to let in or shut out the outside air as needed. Usually mounted into one or several of the walls of your greenhouse, the slats in a louver operate much like mini blinds. Spring for the solar operated ones, if you want the most hassle-free way to vent. When the temperature in the greenhouse gets to a specified temperature, the solar-powered louver activates and opens to let in the cooler breezes and fresh air.

•    Exhaust fans. These are essential for the larger greenhouses, because even a good stiff breeze is probably not going to be sustained long enough to do the job of lowering interior temperatures sufficiently. All of the commercially available greenhouse exhaust fans are resistant to the high humidity of a greenhouse and outdoor weather, and are constructed with built-in louvers, which swing open as the fan comes on. Many greenhouse fans are temperature activated as well, to conserve energy when not really needed.

•    Oscillating Fans.  Sometimes one side of your greenhouse can get considerably hotter than the other, especially if one side gets most of the afternoon sun. An oscillating fan can help to keep fresh air circulating and regulate the temperature throughout.

•    Shade Cloth or Tarp.  In the worst heat of summer, it is sometimes wise to not only vent hot air, but to prevent it from accumulating as much in the first place. That's where a good quality greenhouse shade cloth can make a world of difference. These tarps are designed to let some useful light in, but reduce the amount that penetrate the structure. Because gathered light equals heat, they are generally effective at reducing the internal temperature a good 10 to 15 degrees or more, depending on other additional ventilation measures being used. It is wise to cover the top and afternoon side, and let your plants still get the more indirect light from the walls of the greenhouse, or place the shade tarp in the late morning, and remove it again an hour or two before the sun goes down. You will need to experiment a little to get it right for your area or region.

Ventilating and circulating are two words I never really thought I would need to concern myself with in my new greenhouse. But as I learned the hard way, it's essential to protect your plants from the extremes on either end of the thermometer. I hope you'll benefit from my experience, too.