Archive for the ‘Greenhouses’ Category

Greenhouses Explained

February 11, 2013 4:38 pm
posted by Martin Boyle

Donald asks…

What things are needed to run a greenhouse?

I have a picture of an empty greenhouse and I must fill it in with pictures and explanations of the things needed to run it. Can someone help me by suggesting things I need and their uses. For example an ac heating system, I know one is needed but I don’t exactly know how to explain what it would do. The same goes for solar panels, I know they could help power the greenhouse, but how can I explain that in a more comprehensible way?

Martin Boyle answers: Greenhouses Explained !

I have just finished building a solar room addition. When I put plants in it I will call it a greenhouse.

Greenhouses of any style are an attempt to modify the environment. Glass or plastic walls and roof are often used because they allow sunlight to enter. Inside it becomes heat. There are a number of ways that heat is transferred. One way (radiant heat) is blocked by the glazing. This causes a greenhouse to heat up and even without plants an attached solar room can help heat the house it is attached to.

The things needed to “run” a greenhouse are those things that are first necessary to maintain the environment and secondly are convenient for gardening. My uncle had a commercial greenhouse business. It had a huge boiler that used coal to create heat and send it to the greenhouses. They let most of the heat escape into the air. There was no air conditioning.

Solar greenhouses will sometimes have double glazing to keep heat inside them. As an alternative they may have insulation that is put in place at night to help keep the heat inside them during cold months. The other important thing solar greenhouses will have are a lot of “thermal mass.” This is often brick or stone walls inside of the insulated outer walls or lots of water in containers. The thermal mass soaks up extra heat and when the greenhouse is cool it releases heat to the inside. The effect is to keep the greenhouse from getting too hot or too cold.

There are also designs for greenhouses that use compost that is mixed in a way to heat up. This adds not only heat but can change the air mixture to something that plants will like even more than normal air.

Most greenhouses will not have air conditioning to cool the air. Plants can usually tolerate a bigger range of temperatures than people can. Often there is a way to ventilate the greenhouse in the summer that may be sufficient to keep it cool enough. This is especially true if there is enough thermal mass.

Plants and the ground around them give up a lot of water. If it gets too humid the structure may suffer. Again ventilation may be good enough. Additionally, there are ways to make the heat of the sun create a draft in a kind of solar chimney that will pull air like a fan through the rooms. Ventilation can be aided with vents that open automatically without the use of electricity.

Greenhouses are not all the same. If they are commercial they may be designed for a particular crop. Also the environment where they are built will make a difference. In a cold environment the growing season will be shorter and heating concerns will be greater. In a warm environment ventilation will be more important. In a dry environment keeping water vapor inside may also be a consideration. In a dark environment some consideration might be made about lighting.

Once the inside environment is stable and sustainable some attention may be made to planting concerns: growing beds, soil, water supply and irrigation.

In my greenhouse I just finished I have put a couple of potted plants but it is still freezing outside some nights. My next concern is to get some accurate idea of how the room is heating up compared to the outside temperatures. I have a thermostat for inside and outside but I have ordered one that I can hook up to the computer to log the temperature changes.

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Heating Greenhouses

October 24, 2012 11:32 am
posted by Martin Boyle

Laura asks…

Are there any greenhouses that are warmed entirely by geothermal means and why do they build greenhouses with opaque white plastic covers?

I am curious as to the viability of greenhouses in colder climates producing food year round that are heated entirely by geothermal. My understanding is that geothermal can provide heat to about 54 degrees f. So, a follow-up question would be, are there food crops that will produce at those temperatures? Also why do they build greenhouses with opaque white plastic cover? Isn’t supposed that the more day light, the better for the plants? White color plastic cover on the top of the greenhouses create a shadow all day long. Why don’t they put transparent plastic covers on the top?

Martin Boyle answers:

Good question. I don’t know of any greenhouses that are warmed entirely by geothermal means, but there’s no reason why there couldn’t be. That said, I’m not sure it would be all that cost effective to install a geothermal system just to run a greenhouse, even if you use that energy to grow all your food. If you heat your house that way as well, that would be a different story. I’m also not sure it’d be all that necessary to heat a greenhouse that much unless you live somewhere really frigid. Personally I think the cheaper way to go would be to lay a radiant sub-floor in the greenhouse, and run it with a solar water heater. Cheaper yet would be a solar powered space heater.

As far as your question about plants growing at 54 degrees, yes, just about anything would grow at that temperature (although much more slowly than at say 84 degrees). As long as they don’t freeze, most edibles are pretty happy. Bear in mind though that greenhouses are designed to heat themselves when the sun is out, so it would likely heat up to above 54 degrees on a sunny day without too much trouble.

In answer to your third question : The reason they build greenhouses with opaque white plastic covers [ Polyethylene ]. Polyethylene film is a thick, flexible material that comes in sheets of various thickness (measured in mil) that can be used in single or double layers (for better insulation). A quick and inexpensive option for growers, Farm Tek’s high quality greenhouse film has ultraviolet (UV) protection and offers excellent tensile strength durability. Polyethylene plastic greenhouse film translucency diffuses light well, bouncing the available sunlight and reducing shadows, both of which aid plant growth. Poly film is also easy to install with homeowner tools and modest building skills.

http://www.farmtek.com/farm/supplies/cat1;;ft1_greenhouse_covering_2.html

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The First Person To Use The Phrase Greenhouse Gas

October 18, 2012 11:33 am
posted by Martin Boyle

Sharon asks…

Who was the first person to use the phrase greenhouse gas? And when etc. Cheers?

Martin Boyle answers:

Svante Arrhenius (1859-1927), was the first scientist to propose that fossil fuel combustion may eventually result in enhanced global warming in 1896.

He found that the average surface temperature of the earth is about 15 degrees C because of the infrared absorption capacity of water vapor and carbon dioxide. He was the first to call this “The Greenhouse Effect” and, thereafter, the gases which contribute to the effect became known as “Greenhouse Gases”.

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Ants In My Greenhouse Are Eating My Vegeatables.

October 17, 2012 1:46 pm
posted by Martin Boyle

Thomas asks…

Ants are eating my young pepper plants in the greenhouse.The usual powders etc do not appear to work.

Does anyone have any ideas.

Martin Boyle answers:

Stand the trays or pots on legs and then rub a thick clump of Vaseline around the bottom of each leg, Or around the top of each pot! The ants can’t get through it.

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Planting Out Seedlings In Maine

1:37 pm
posted by Martin Boyle

Susan asks…

Is it OK to put vegetable seedlings outside during the day?

I started tomato and pepper seedlings about 2 weeks ago. They are now about 2-3 inches tall. I have a unheated greenhouse and was wondering if it was OK to put the seedlings in the greenhouse during the day, when i leave in the morning it is in the 30’s and when I get home it is in the 50’s outside. What is the minimum temperature that seedlings can handle? I Live in Maine.

Martin Boyle answers:

You shouldn’t put them out there if the temperature is under 32, but it would be very good for them to go out there when it’s between 45 and 70. It’s probably warmer in your green house (even though it’s not heated) than right outside. This will also help harden your plants so they won’t have so much shock when you actually plant them outdoors. Good luck and have fun! 😀

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