Greenhouse Question

[dooleysm]

My wife and her siblings gave their mother a 'greenhouse' for Chrismtas in 2008. Actually it was a promise to build one for her. For a variety of reasons, mostly based on laziness, they haven't gotten around to building it until now. MIL really only needs this greenhouse for starting plants for her garden, so she really doesn't need or want a big walk-in type deal.

What they've ended up with is basically a 4x8 box with a slanted glass roof. Seems reasonable to me. I think if they point it South it'll collect enough light to start seedlings. My concern is heat. MIL normally starts her seeds in late Feb., and we are currently still getting freezing temps (not unusual). So, my question is, what is the best way to heat this box?

As I see it there are 2 options, a heat light or a small space heater. It is my belief, though it's been a long time since I was in biology, that plants need some period of darkness as part of the photosynthesis process. If they put a light in there for heat, it would have to be on potentially 24 hours at a stretch to keep the plants from freezing. That said, I feel like the plants would benefit from some extra light to extend the days. Maybe a combination of a space heater and a flourescent light on a timer? Are there any other options? What do you master gardeners think?

 

[ToadHill]

I'd heat durring the day and cover the unit with a quilt at night.

 

[Chuck52]

One of the seed sprouting heating pads might be a good way to go. If the box is reasonably well insulated that might be all the heat needed. I have a couple that I use under the trays until the seeds sprout, and then, because my seedling rack is indoors, I usually don't need the additional heat because the grow lights I use provide plenty.

Those pads can get expensive, but a small one can usually be found for $30 or so. I just bought a professional grade 36"x16" pad from some folks who were planning to move and were getting rid of their excess stuff. I paid $30 for that pad and a 4' three bulb grow light, so you can sometimes find deals.

In your case, I'd probably test the set up for temperature before committing the seeds and seedlings to it. Those pads don't put out lots of heat because you don't want to cook the seeds.

Chuck

 

[Kays Supply]

I was in a house the other day that had a heated ceramic floor. That was a large area. You might be able to adapt that to your needs.

 

[dooleysm]

The box is about 3'x7'. Not insulated at all, just osb walls and floor and a hinged glass door for a roof. Would make a nice reusable casket I think. It sounds like the heating pads would not be ideal for that. MIL starts a load of plants for herself and others. She will likely fill that space with mostly tomato plants.

 

[jinman]

Shawn, in a such a small area, a grow lamp might be just the ticket for light at night and enough heat to keep the inside above freezing if it is sealed pretty well. I think from bright sunlight during the day to the glow of a grow lamp at night will provide plenty of variation. I don't think definite day/night cycles are needed for young growing plants. Flowering/fruiting plants later in the season may need the daily cycle, but I think young plants can grow 24 hours per day.

 

[CosmoAU]

It is my belief, though it's been a long time since I was in biology, that plants need some period of darkness as part of the photosynthesis process.

This is correct. I saw an experiment when I was at AU with this on corn. With normal light/dark conditions the plants were 3-4 ft. tall. Interrupting the dark period with just 1 hr. of light left them less than 1 ft. tall in the same time periods of growing. It was a pretty interesting experiment for a dumb ole country boy. :laughing:

 

[Jstpssng]

How cold does it get there at night? This time of year you shouldn't need much heat during daylight hours; even on a cloudy day you still will get energy from the sun. For that size building I would suggest several black 55 gallon drums filled with water, implemented into the bench system. These will store heat during the day and release it at night. However, a small thermostatically controlled space heater would be a good idea for backup. Also, foam insulation inside the OSB would be a good idea.


I would suggest putting a Hi-lo thermometer in it to find out the temperature ranges. I'll bet she finds she has to ventilate on sunny days.

P.S.; the nightly quilt or other insulating agent would also prove helpful. On cold nights at my parent's greenhouse we used to unroll woolen blankets (made for the purpose) over the cold frames.

 

[forgeblast]

I also have an unheated green house a lot like the one your talking about. its 8x10, with a palroof (clear plastic panel roof). What i do is start the seeds indoors, (ihave my cabbage, brussle sprouts, and leeks started now). They are started inside the house with the little plastic dome things you can buy at any box store. then i use the green house to harden off the plants. by spring when the thaw hits i can move more plants out to it, right now its the winter garage for my little lawn tractor.

 

[LRTX1]

I have used those little candles, tea lights I think. You can get them pretty cheap at a dollar type store. 6 or so in a metal pan will generate quite a bit of heat in a small space for 3 or so hours. All you really need to do is keep it from getting below freezing inside. Even if it does drop below freezing, just as long as it is not for an extended length.

The space heater would be the less maintenance throughout the night though.