Day 1

[Millet]

Yesterday was the first day this season I had to close the greenhouse tight due to the cold overnight temperatures. It got down to 30-F . - Millet

[brian]

I took a risk last night.  32F for 2-3hrs and frost according to NOAA.  I moved my lemons and limes inside and left the oranges, mandarins, kumquats, and finger lime outside.  Hopefully all is well.  Everything will need to move into the greenhouse soon but I haven't had time to finish the work I want to do there. 

[Millet]

NOAA is just a few miles from my place. - Millet

[brian]

NOAA is great, a government entity that really seems to have their stuff together.  Weather.gov beats all the commercial weather services by miles.

So far I see zero damage, even to tender new growth.  I'm not sure how long damage would take to appear but I'm relieved so far.

[brian]

It's 30F outside here and 70F inside my greenhouse from sunlight alone.  A few of my trees are pushing out new growth.  Winter is now like an early spring, it's great.

[Millet]

Greenhouse grown citrus trees will frequently flower in January. - Millet

[Blake Branch]

Millet,

What temperature do you set your thermostat in your greenhouse?

[Millet]

i have two overhead Modine heaters in the greenhouse.  One is set at 55-F, which is  the lowest setting the thermostat goes for that heater.  The other heater is set at 45-F.  I set them this way in case one of the heaters fails on a cold winter night, the second heater will come on  to keep the greenhouse from freezing. The chance of both heaters failing on the same night would be very rare. I also have two additional heat back ups.  Therefore, the greenhouse gets down to 55-F, or a few degrees lower on very frigged nights.  I grow some tropicals that are not supposed to go below 55-F. For citrus one wants nights at least as low as 55-f to enable the trees to set a good bloom come spring.  Also, cool nights helps color up citrus to a good orange color. - Millet.

[Daintree]

Millet,
I have questions about your heaters!
After this latest cold snap, I have been looking at the Modine Hot Dawg heaters.
I just have a blue flame gas furnace right now, and some parts of the greenhouse get much colder than others.
Do you find these heaters are fairly economical (I mean, considering the temps we deal with in Idaho and Colorado...)?
Where did you get yours?  I was looking at the catalogue from the Greenhouse Megastore.

Also, I don't understand why greenhouse heaters are mounted high on the wall.  Seems you'd want to put more hot air down where the plants are, and let it warm the area from the bottom up.

Thanks for any info!
Carolyn

[Mark in Texas]

I highly recommend Reznor UDAP type heaters.  Better quality than Modine IMO and a better value if you shop Ebay and such.  Greenhouse Megastore is over priced.

I'm growing all kinds of tropicals and the temp goes down to 34.5F where the controller is set.  If they don't like it, that's tough.     Been doing it for about 3 years with no problems.

This is my backup in case electricity goes out.  http://www.homedepot.com/p/Dyna-Glo-50K-80K-LP-Convection-Heater-RMC-LPC80DG/202895381?N=5yc1vZc4kf

Mark

[Blake Branch]

I use L.B. White heaters.  I lucked up and bought 5 210,000 btu heaters from a tropical foliage nursery down in Apopka, FL for $900 total.  The nursery was going out of business and selling everything. 

The primary reason for high mounts on heaters is to keep the heater out of the way, and provide an unabstructed area for the heat to be blown across the house.  I built a mount for the heater to sit on in the greenhouse.  It sits about 18 inches off the ground. There are 4 horizontal air flow fans in the greenhouse that are angled downward to blow the rising warm air down onto the plants.  The two on the right side blow to the back of the greenhouse and the two on the left blow to the front.  This helps to keep a more even temperature across the area.

As a side note:  Most of the weather services were close on Tuesday night.  We got down to 22.  All of the weather services , including NOAA, were off for my area last night.  The forecast was for 29 and we got down to 23.  I was late turning on my water in the field, and some of the microsprinklers had already stopped up with ice.

[Millet]

Daintree, some greenhouses do have their heaters place so that the hot air is blown under the plant benches, however when attempting this type of heating there is a lot of obstruction to the air flow. .  Personally I much prefer over head heaters, which as Blake wrote, with  high mounted heaters the hot air can be blown unrestricted all the way to he back of the greenhouse.  I have three large flow fans spaced throughout the greenhouse which blows the heated air back down to the plants, plus horizontal fans circulating the air around the greenhouse at plant level.   These fans keep all sections of the greenhouse at much the same temperature. - Millet

[Daintree]

Thanks everyone! That is a huge help!
22 in Georgia - brrrrr!