Greenhouse Tips

[alamo5000]

I built a greenhouse this year, about 6 weeks back to be exact.

I built a pretty big one...it is 12 foot wide by 30 feet long...

Now we are bearing down on the first real freeze tonight (below 30 degrees easy) and here is what I have already figured out...but first some details...

My greenhouse is within extension cord distance...also I have a remote thermometer (47 bucks) that tells me the history of the temperatures inside as well as a current reading and humidity...

Last night it got cold (mid 30s), but I noticed with my little heater (again, a pretty good one, about 60 bucks worth from Lowes) my inside temps were staying about 10 degrees or 15 degrees warmer than the outside....

so theoretically if it got to 10 degrees outside (which is rare here) my plants would still be below freezing despite the heater. I am not sure if the logic is right so if I am wrong let me know.

I have a second heater so in order to run a test I plugged that one in too...the result? I nearly burned up a brand new $50 extension cord.

I currently have 40 tomato plants (in 5 gal buckets) plus several other plants inside. I was able to rearrange everything and fortunately I had more sheet plastic laying around so I made another partition inside the greenhouse. You know what? I STILL have space left over even after putting three ferns and three big flower pots inside (my mom doesn't have a place to over winter her plants).

As of right now things are going pretty good with it but I will know for sure in the morning.

The moral of the story? While you may dream of having a huge big old greenhouse, there is such a thing as having one TOO BIG.

Also just based on my rough data so far with a single normal extension cord and a fairly decent electric heater one can effectively heat a space approximately 12 foot wide by 18 feet long (down to about 20 degrees or so)...I would say thats probably the limit.

If you are thinking about building a greenhouse by all means be practical. Build one only enough for what you want to use it for. Kind of like going to a buffet when you are a kid and your eyes are bigger than your stomach....same principle. You don't need a shotgun to kill flies.

If you are thinking about building a greenhouse keep these things in mind.

Just my 2 cents from a newbie who is still messin stuff up from time to time.

[Mrs.B _in_WY]

I vividly recall my dear mother telling me my middle name was "overdo." It's as true today as it was then, so I can tell you if I had an opportunity to build a greenhouse the size I need versus something larger, well, it's a pretty good bet I'd go larger. Besides, I'd be surprised if you didn't read or weren't told something along the lines of "Go as large as you can afford. You'll always find more things to put in there."

I know you did extensive research before you started, so I'm wondering what that research had to say about using heat sinks. For most people, the heat sink takes up too much of the greenhouse space. In your case, I wonder if that could be a plus rather than a minus.

I haven't been in it since it was extensively remodeled, but Cheyenne Botanical Garden's greenhouse (now plural) used a north wall of those 55-gallon poly barrels as a heat sink. They were stacked several high and painted black. Before the photovoltaic system was installed, the people there used to joke that they figured it was the only greenhouse that cost more to cool in the winter than to heat in the winter. This page doesn't have technical details, but it might give you some ideas.

http://www.botanic.org/More_Details.asp

Just a thought. I hope everything survived the night in good order.

[alamo5000]

I actually didn't research as much as I should have

I don't know what a heat sink is... never heard of it...

From where you are at I am way south so normally we don't get super cold weather. Last night it got all the way down to 24 degrees. I have a little gadget that is calibrated and all that so its very exact.

In extreme cases it can get down to the teens, although it doesn't happen all the time. Here, last night it was cold, but its gonna get up to 60 in the daytime. Thats generally what I am dealing with.

My partition that I made saved my bacon last night....my remote thermometer said inside the greenhouse it dipped down to 42 degrees. Thats INSIDE the greenhouse. My plants all look great.

I honestly started building the greenhouse sheerly because I wanted a greenhouse. The whole thing (not including the heater etc) was around maybe $300. I could have done it for maybe half that had I chosen to do a smaller one.

This is my first greenhouse so most of it is trial and error.

To me, the big greehouse is great. Its nice when its not 'too bad' outside...When the tire meets the road though, for a hard freeze, the big one is too much to keep warm unless I partition it off or decide to hard wire some more electric plugs out to the barn...in the end its both good and bad to have a big greenhouse.

I have a lot of ideas on how to build a great greenhouse, but if I did that it would cost me $10,000 or more. I am trying to stay on budget here.

[Mrs.B _in_WY]

For sure we're dealing with dealing with nearly opposite ends of the weather spectrum, and I didn't do a good job of explaining "heat sink"

The black barrels I mentioned the Botanic Gardens uses are filled with water. They absorb solar energy during the day and radiate it back as warmth during the night. Some people get fancy and install a circulation system through their water heat sinks. In a really cold climate or if too many days go by without sufficient sunshine, a heat sink can work against you. If the water gets really cold or freezes, instead of radiating heat during the night, it radiates cold. Not helpful. People use other things for heat sinks, too. Sometimes the floor is designed to absorb heat. Sometimes people use rocks (either in the greenhouse or as part of a wall).

'Glad your plants are happy this morning.

[habitat_gardener]

Originally Posted by alamo5000

I don't know what a heat sink is...

Also called thermal mass -- something that will absorb heat on sunny days and release it when the air temperature ("ambient temperature") drops.

[amideutch]

Don't know the construction details of your greenhouse but if you could build plastic lined panels that could be attached to the outside of the greenhouse to create a dead air space and still allow the light to penetrate, this would increase the insulation factor of your green house. Is your greenhouse, lengthwise, running north-south or east west? Ami

[wordwiz]

Mine is 12x16 feet. I used 13-mill, fiber reinforced plastic for the roof, glass windows for the front and sides. The north wall is plywood with R-19 insulation, covered with Mylar. Inside, I covered the walls and top with Greenhouse AC plastic, giving me a dead air space.

For an extension cord, I used a 12/2 with ground electrical cable on a 15-amp fuse. It powered a 1200 watt and a 450 watt heaters, two 80-watt lights, a 30 watt air pump, a small radio and a fan.

I was able to increase the temps 30 degrees of a night, meaning I did not need the Kerosene heater unless in was going to be colder than about 20. Living in Cincinnati, it did often get that cold but I used only about 10 gallons of kerosene the entire winter.

Mike