I have two propane heaters as the ultimate, last-resort heaters. I have never had to use them..............knock on wood.

Probably goes without saying, but... just make sure propane heaters are either properly vented or are a "ventless" type. (Don't want to lose any of our gardeners to carbon monoxide poisoning!)

Indeed!

Mr. Heater has a ventless one but that's probably over kill.

I use Southern Burner Heaters, they are in Oklahoma, google for. Website. These are natural gas or propane. Expensive, but mine are about 18 years old and flawless. They do not require electricity to operate and when others have lost plants, mine have been great. Mine are vented. I cannot say enough in their favor.

We use a forced hot air heater fueled by an outside woodburner at one end of the greenhouse. At the other end we have an oil filled radiator type electric heater with a thermostat. Our greenhouse is 40' long. We keep it at an average of 60 degrees at night.

@cparsOns. Your greenhouse is huge compared to my two. My heat is all electric, now 240V forced-air heaters in each. I too keep my greenhouses @ 60F minimum.

Ours is 13x40. We just love it. It is a lot of work though as I am growing to sell at our local market. I enjoy it. :)
I found this forum because right now I am battling slugs on my coleus and aphids on my mandevilla.

Good luck with the pests. It's a never-ending battle.

Hi Cindy and welcome! Get some Diatomaceous Earth, DE - totally inorganic - you'll also need one of those pump dusters but that will take care of the slugs. Put some down at the base of the plants and some on the top and bottoms of leaves. Good for greenhouse insect control but not a good idea outside because it will kill good insects as well ... DE is tiny shards of diatom shells and for insects and slugs it's like walking over broken glass. For the aphids, I take a small stiff paintbrush, dip it in insecticide and brush them off the plants. Here in my zone 8 I have a whole colony of anoles living in the greenhouse and they do a pretty good job of insect control for me.

Thank you so much! The paintbrush sounds like a great idea! I use the DE in my chicken coop but never even thought about it for the greenhouse. I tried the beer trap for the slugs last night but I didn't catch any.

What temp setting do you set your milk house heater when connected to portable thermostat?

Xeramtheum said: How big is your greenhouse? I use the force fan milkhouse electric heaters with a portable thermostat and have a box fan up high to circulate the air and heat. My GH is 8 x 16 and one heater does the job though I'll put two in there when the temps will get into the 20's outside for more than 2 or 3 hours. They system adds generally about 50 dollars to my electric bill every month. The picture shows 2 heaters, one high and one low.

Here is a link to the portable thermostats I use

I was reading all that thinking how did this long long thread get here without me noticing. Then I noticed the date. Exactly 6 years ago today!

The temperature setting depends upon what you are growing. My greenhouse temperature is set at 60 because I grow orchids. My daughter's is set at 35 because she grows citrus trees. I could set the thermostat at 55 (and daughter at 30) but the heaters don't keep a constant temperature the way your house heater does. A little built in safety net.

Yep, Daisy, my three greenhouses back in Mississippi were also kept at 60 F because of my extensive collection of orchids. Before I moved to Florida, I had over 200 varieties and over 500 orchid plants. I grew a lot of other tropicals too, but orchids determined the thermostat setting. Now I just have a shadehouse, a smallish 12x20' one, and I only have a couple hundred orchids. I'm doing more with plumeria now than with orchids.

I'm getting a head start on some early tomatoes which I want to keep the temperature in the 70-80° range. Once I get my new portable thermostat I will set it at that range but need to find out what I should set the milk house heater dial to that's going to be plugged into the thermostat. I was thinking not all the way up but somewhere in between. The thermostat that's built into the heater is all over the place in temperature which is why I ordered a external one.

DaisyI said:

I was reading all that thinking how did this long long thread get here without me noticing. Then I noticed the date. Exactly 6 years ago today!

The temperature setting depends upon what you are growing. My greenhouse temperature is set at 60 because I grow orchids. My daughter's is set at 35 because she grows citrus trees. I could set the thermostat at 55 (and daughter at 30) but the heaters don't keep a constant temperature the way your house heater does. A little built in safety net.

For my current milk can heater I just use its built in control. The stuff I am growing isn't fussy enough to bother with an external thermostat. With the external thermostat, you need to have your heater on the "high" setting for energy and the dial turned all the way as warm as it will go. Otherwise at 70-80F your heater's internal thermostat will interfere with the functioning of the external one.

You might consider getting the greenhouse to 60F and then put heat mats under your tomato trays. Until they are a few inches tall, they are much more concerned with soil temperature than room temperature.

I agree. I had 240V heaters and even with these expensive, powerful heaters, I never trusted their internal thermostats. Set the temperature higher than you ever want it and the thermostat will control the temperature to a .5 F. I loved my remote thermostats.

Thanks for the great tips! I'm so glad I found this group.

Have fun with your greenhouse!

Winter here can be extremely cold (-35°F) with sunny days. So I designed a collection system with a salvaged flat-plate water heater on a loop charged with 50% glycol antifreeze. The small PV panel drives a DC pump to circulate the loop.



There' a 400 gal. heatsink under the floor, with coils of PEX tubing carrying the heated glycol solution through plain water. An AC pump circulates the warm water through the floor, which is the main thermal mass.



Besides the dark pavers and black pots, there are four 75 gal. plastic tanks on the south-facing wall, passive heatsinks.



I took apart electric quartz radiant patio heaters and mounted four elements on the ceiling, wired to a hanging thermostat. They warm the foliage even when the air temp is quite cool (often around 40°F).



When it gets down to -20°F or so, I add a small milkhouse heater, with a small propane catalytic heater as backup, in case the power goes off.



The foundation and floor are insulated. The roof is 6-wall poly (R 3.8) and the sides are 3-wall. When it dropped to -40°F, I lost a few plants to cold air leaks, but have grown tomatoes year-round since 2009.