My "hot" grow bed
This spring has been cold and wet. We’re a few days away from May and it is still cold and wet. Fearing a year with wimpy tomato production (again), I took some drastic measures. I created a “hot” grow bed in my greenhouse. You’d think the greenhouse alone would be enough to warm up the beds. It helps, but without sun we’re not getting good tomato and cucumber soil temperatures yet.
Cold grow bed
Here, you can see another bed in the greenhouse that has not been made into a hot bed. There is a 14 degree temperature difference.
So, what is a hot bed? If you think of the seedling heat mats you use indoors, a hot bed is kind of like that, but on a larger scale. This hot bed uses heating coils and electricity. Here’s how I put it together.
Heating cables attached to hardware cloth
First, I ordered soil heating cables. The cables were then attached to a piece of hardware cloth in order to keep them straight and evenly spaced in the soil. This cable is 36′ long, using 126 watts of power. The energy usage is definitely a consideration and I plan to unplug the coils as soon as the other beds in the greenhouse catch up temperature-wise. This is merely at attempt to jump-start the season given the terrible weather.
Planting the hot bed
After getting the hardware cloth and heating cables in place, I installed the tomato cages, making sure they did not push into the heating cables. Then, I began planting the tomatoes. I have to admit, this was a pain to do with the tomato towers already in place.
Tomatoes, growing in the hot bed for one week
The tomatoes have now been in the hot bed for a week and they are doing really well. I’m seeing lots of new growth and the color of the plants looks wonderful.
To offset the electrical usage, Derek and I have been discussing installing a solar panel on the greenhouse. This could be a good way for us to get started with solar, something that continues to be part of our long-term plan. I must acknowledge it does strike me as a bit funny to use a solar panel to create electricity to warm the soil in what is already a passive solar greenhouse, but gardening in the cool Pacific Northwest brings with it many challenges.
I fully understand that this kind of set up is not for everyone. Most gardeners do not have a greenhouse and those who do probably don’t have electricity available in their greenhouse. Even so, I wanted to give it a try and it will be a fun experiment to see if this set up makes any measurable difference in my tomato harvests this year.
Sandy
The 10 Year Challenge 
I am such a garden geek! I find stuff like this terribly interesting. Putting up some solar collection to offset the energy use makes good sense. It will be interesting to see how long you need to have them connected before the soil naturally warms up enough to carry on at the same level.
I’ll follow what you do this way, too. I have a heating cable in a large box covered in sand in the unheated greenhouse; it’s my “heatmat”, and this is my second year trying not to cave to grow lights. (Though seeing Laura’s January tomatoes may tip me over the edge!) I wondered about the solar panel too; it seems a no-brainer. Except that the cheap, small, hardware-store panels (on sale this week for $85) only produce 15W! Puts those 250W heat lamps and 100W heating cable in perspective! When we start doing the solar math, I really start to respect the design of the earthship-like passive solar homes and the true volume of power that we use everyday. CFLs only go so far! So far my deep raised beds under the cold frames seem to be really holding the heat. But I suspect we’re getting a little more sunshine than you, even though we’re a zone colder. Good luck and keep us posted!
Laura’s January tomatoes made me buy a grow light system. it was around $65 and I love it. I can’t imagine not having it now. But that means I’m running electricity for a few months which is probably the same thing as your soil heater. My tomatoes finally look as big as hers though – I actually have fruits on some and flowers on most of my bushes already, though they are all early or ultra-early this year.
Not sure if you have seen this yet: http://cliffmass.blogspot.com/2011/04/pdo-and-long-term-trends.html but if it’s true you will be using your soil warmer a LOT.
Thanks for that fascinating link, Annette–depressing and hopeful all at the same time, perhaps?!
Yea! I LOVE techie things…but I can’t help having a bit of a giggle as well…when even something as natural and simple as a garden gets electrified…*: )
Hi Sandy, Just skipped over from Toni’s Backyard Feast (don’t know why it’s taken me so long) and was admiring your hondo tomato cages! If you don’t mind me asking, where did you get them? I’m really tired of these wimpy round three-legged things that pitch over if you look at them sideways!