How does a Greenhouse Work?

How does a greenhouse work? It's a good question that needs to be answered in order to understand how to get the most out of your vegetable gardening.

The basic operational principles of greenhouses include: collection of light and conversion to heat; storage of thermal energy; release of thermal energy; temperature moderation; controlled environment; and, protection from severe weather and animals.

Let's get a good look at each of these functions.

This is probably the best way to get a feel for how a greenhouse performs in a way that you just can't achieve in a traditional open sun garden space.

How does a Greenhouse Work - like a giant solar collector

I've heard people speak a solar greenhouses as if they were something different than other types of greenhouses. My understanding is that all greenhouses are solar greenhouses - they convert light to heat.

Without getting into a discussion of the wavelength of light, let's just imagine that a greenhouse is very much like a car with its windows rolled up. The sun penetrates the glass and warms up things that are inside.

How does a greenhouse work? Very much like a car parked out in the sun.

Dark materials warm up quickly, and light materials warm up slowly. The warmer materials inside the greenhouse help heat the air within, and since it's a closed environment, the breeze doesn't blow away the warmth. It's allowed to accumulate.

Now think of the same dark and light materials outside where there might be a nice breeze. Any warmth that might be accumulated is quickly swept away with the constant air exchange. You don't feel so much warmer just standing in the sun, but if you're inside a car, you'll soon roll down the windows.

How does a Greenhouse Work - thermal storage

Once the light is converted to heat, part of that heat is naturally stored in objects present in the greenhouse. You'd be well advised to deliberately place items with good "thermal mass" inside the greenhouse to allow them to absorb and store the heat that is created within.

Thermal mass can be achieved with moist soil, bricks and water. These items are ideal because they absorb thermal energy slowly and release it slowly back into the greenhouse once the sun has down.

How does a Greenhouse Work - thermal release

Once you're successful in storing thermal energy, you'll want to release it during times when the sun isn't shining. That, of course, is the entire reason to store it in the first place.

Fortunately, This will occur naturally without any help from you. Thermal mass like water and soil will absorb heat slowly and release it slowly. Thermal mass like iron will absorb heat quickly and give up (emit) heat very quickly as well, providing little benefit to your greenhouse throughout the night.

How does a Greenhouse Work - temperature moderation

You've probably heard of "the lake effect" with respect to large bodies of water such as the Great Lakes that surround the State of Michigan. They represent tremendous thermal mass and therefore keep temperatures in Michigan relatively moderate throughout the year.

Greenhouses do much the same thing if they're large enough and have sufficient thermal mass within. They heat up slower and cool down slower, so they help moderate the temperature inside. In other words, they reduce high and low temperature swings.

Vegetable gardening will require consistently higher temperatures for cultivars like eggplant, so having the ability to moderate the temperature will be important. Also, reducing the highs and lows in the greenhouse will keep you from sending mixed signals to some of your vegetables that might cause bolting, failure to set fruit and slower growth.

How does a Greenhouse Work - controlled environment

Hand-in-hand with temperature moderation, a greenhouse should also have features that help control the environment. Not all features are required, but they should all be considered. The following features could be used to make certain your greenhouse gardening experience is optimal:

• lighting - so you can see in the evening
• ventilation - to let in fresh air and exhaust hot air
• circulation - keeps air from becoming stagnant
• heat - helps take the edge off of winter
• misting or fogging - for cooling the interior if ventilation isn't adequate

I find that ventilation is key to reducing temperature extremes and allowing air circulation. If you don't have adequate ventilation, the answer to how does a greenhouse work? will likely be: "Just like a giant warming oven." And, your plants will suffer without relief.

How does a Greenhouse Work - protection

In addition to keeping things warm, a greenhouse also serves as a way of protecting plants from severe weather - severe in terms of how your vegetables see it. Here are some examples of severe weather and how the greenhouse meets these challenges:

• strong and dry winds - enclosure blocks the winds
• sunburn - shade cloth or white wash can be applied
• hail - woven poly fabrics are almost impenetrable
• driving rain - greenhouse cover sheds rain
• excess heat - fogging and misting systems cool the interior
• insects - enclosure and screening can limit their access to the plants
• pets - doors and high sides keep out pets
• critters - foundation and enclosure keep out all but the flying varieties

Physical protection from driving rain, strong and dry winds, and hail is perhaps the most important answer to how does a greenhouse work for those of us who live in semi-arid climates like Wyoming where we have lots of wind and hail.

Recognize that the greenhouse won't be impervious to all animals. If you have aggressive diggers or small flying insects, they'll be able to tunnel under and get in through vents. Also, ants will bring aphids inside your greenhouse from underground, so you'll still have to watch for unwanted invaders.

Also, you'll not want to keep all manner of insects out because the bumble bee will be one of your best pollinators. You'll want to allow them in during times when your squash is blossoming, unless you want to practice manual pollination.

How does a Greenhouse Work - wonderfully for me, and it will for you too

If you're looking for a more stable environment for vegetable gardening and you'd like to intensify the regular growing season as well as extend it, you'll want to take a careful look at greenhouses. They offer an opportunity to get a jump on the season, extend it, and greatly increase vegetable production.

Greenhouses also offer protection from weather and animals that is hard to achieve in open sun garden beds.

If you're serious about vegetable gardening, and the idea of a year round harvest appeals to you, you're probably ready to make the necessary investment now that you know the answer to how does a greenhouse work?

The key choices now are: purpose; location; size; style; kit or homemade; features; and, start date. Think long and hard about these matters as even smaller greenhouses require commitments of time and resources to make your vegetable gardening a success.

Done with How does a Greenhouse Work, take me to Greenhouse Gardening