personally i think it will be a real challenge to start seeds in a non heated greenhouse. i think damping off will get the majority of the tender sprouts, due to the cool starting media.

i usually use jiffy mix.

I dont know if you have used your HF greenhouse to start much. but i have a 10x12 and it was real frustrating to have to constantly monitor the inside temp. the wind would whip the roof vents or the doors needed open or closed all the time.I'm sure you've noticed it gets real hot on sunny days.

you might be able to get some plants started with heating mats to set under the trays. i have been starting mine in the 4x8 trays and transplanting to more trays as needed. but i do it to sell the plants.

i guess you could run the small heater on cold nights and see how well it does. i know that increases costs.

i have gone to the hoop type,double layer greenhouse and outfitted it with exhaust fan,intakes,thermostat to help control the temp. blus a blueflame heater with a therostat. expensive to say the least to run. i still have to manually turn the heater down on sunny mornings or the intake air will tell it to heat. cloudy days are the worst. greenhouse stays pretty warm but still need some air exchange at times.

Now if it was me, i would put some foil back insulation on the bench to keep the hat concintrated to the tray and use a heat mat to start my seeds.

I was hoping busy1 would see your question and respond because if anyone knew if it could be done, it would be him.

I start all my vegetable seeds indoors on a homemade light shelf that holds 20 flats (if I cram them in) or that easily holds 15 flats. Once the plants are a couple of inches tall, I carry them outside to the screened-in porch where they happily spend winter days in bright light and coolish temps (or warm ones if it is a warm, sunny day). At night, if I think the back porch temps will stay above freezing, I leave them out there. If the temps are likely to go slightly below freezing, I just throw a Reemay frost blanket over them. However, if it is going to be very cold, I bring them back inside. Cold weather can kill some small seedlings very quickly. I've never lost seedlings left out overnight on the back porch, but it has insulated walls and an insulated ceiling and it still gets very cold. I cannot imagine leaving small seedlings in an unheated greenhouse, and even if you heat it, as Busy1 noted, you will have to be sure there's good ventilation to prevent damping off and other disease issues.

I'd suggest you get a Min/Max thermometer if you don't already have one, and keep a daily log of your greenhouse highs and lows, beginning as soon as possible. Also keep a record of your outdoor lows and highs so you can compare outside air temps with your greenhouse temps. By tracking the temperatures that way, you'll be able to determine how much warmer the greenhouse stays at night (if it stays warmer at all) and also how hot it gets during the day. That will tell you if it is warm enough to start seedlings in it.

The biggest misconception I think most people have about greenhouses is that they think the greenhouses stay nice and warm at night, which isn't really true. Without a heating system, they get just about as cold as the ambient outside temps.

If you do as Busy1 suggests and use a heating mat and reflective insulation, that will help quite a lot. I still think you'd have to throw frost blankets over seedlings on very cold nights. It only takes one night of too-low temps and you could lose every seedling in the greenhouse.

In addition, there's the issue of seedlings underperforming later on because they were too cold early in their life. That's a particular problem with pepper plants, which need to stay consistently warm and cannot tolerate very cool nights the way tomato plants do. If pepper plants are subjected to very cool yet above-freezing temperatures early in their life, they can remain stunted and unproductive for months, and sometimes for the whole growing season.

Dawn

Speaking from my experiences with my unheated greenhouse in OK:

1. WHEN TO START (as it is non-heated), if heating required for jump start, I have one small fan-heater from HF.

I started the same time as usual. I kept the seeds inside until they germinated, then moved them out to the greenhouse.

2. POTTING MIX- which is best potting mix/seed starting media;

Seedless mix. Sometimes I used Jiffy mix, sometimes mixed my own.

3. CONTAINERS- what kind plant containers suited, should we use flats or large container for initial stages or small pots for individual seeding?

Depends on the plant and what I had on hand. I always used smaller ones that would fit in flats so that I could carry in and out. During the beginning, nights were cold and I'd have to carry back inside the house or they'd freeze.

4. GH Floor, should I directly seed on the greenhouse floor (either side of the wall)

I have no experience with direct seeding in the greenhouse.

Have fun and experiment! I loved having a greenhouse!

Diane

Thank you Busy1, Dawn and Diane,

Those are very useful tips and cautions! I will try your options and also do some experiments with Frost blankets, seeding on GH floor and I hope water tub's (west side) may provide some heat... I am taking risk to waste some seeds. However I also thinking to buy grow lights or try to build one myself, Dawn do you have posted any thread on the homemade light shelf you have built?

FYI, some of the vegetables and plants such as cilantro, spinach, dill, herbs such as mint, sage, oregano, thyme, etc still doing well in that non-heated GH. I also noticed that water lettuce and water hyacinth still holding their life in water tub. I am not sure about Next Week's Artic Blast of Cold Weather will keep them live :-(

Thank you -Chandra

Chandra, I have described it before, but don't know if any of those threads are easily found by a search. The Garden Web search function works erratically at times.

It is easy to make a light shelf though.

We bought a plastic, assemble-it-yourself shelf at Home Depot. It had five shelves, and the shelves were about 38" long and about 22" deep. (That's just a guess, but probably isn't too far off.)

We bought standard shop light fixtures. Each one holds two fluorescent tubes. For each shelf, we have two fixtures which equals four tubes.

The lights are suspended from the shelf above them with chains and hooks, so I can raise and lower the lights as needed. In order to light the flats on the top shelf, we put 4 plant hooks (2 per shop light fixture) into the ceiling above the light shelf and suspend the chains holding the fixtures from them.

All the lights are plugged into power strips, so we can turn the lights on or off by turning those two power strips on or off. I turn on the lights in the morning after I get up and turn them off at night before I go to bed.

In that particular room, we close off the central heating vent because all those lights really heat up the room and sometimes I even have to open a window to let cool air into the room to cool down the room, which faces south and west.

We use plain old ordinary fluroescent tubes and don't spend more money than necessary for anything fancy. I raise thousands of seedlings successfully using this light shelf every year.

I can easily line up three flats lengthwise on each shelf, Or, if I turn the flats sideways and let a small portion of each shelf hang off the edge of the shelf, I can cram 4 flats onto the shelves.

I'll see if I can find and link a photo of a shelf similar to what we use.

Dawn

Here is a link that might be useful: We Have This Exact One

Thank you Dawn, pretty good instructions, will build this weekend. -Chandra

Chandra,

You're welcome. If you put this light shelf in your greenhouse and turn on all the lights during the afternoon, they might heat up the greenhouse enough to get your plants through the arctic cold spell, depending on how cold your forecast temps are supposed to be.

When I have all the lights on the light shelf all day long, the room gets too hot so I have to open the window to let cool air in. Of course, that's in an insulated room in a house. Still, the lights might make just enough heat to keep the greenhouse warm.

Otherwise, I think covering the plants with frost blanket type floating row covers can give 4 to 8 degrees of protection. When I use a floating row cover in winter, I use a double layer to increase the amount of protection it gives.

I don't think any of my garage plants are in trouble next week because I don't think we'll get that cold here at the southern end of OK. The plants have already survived low temps down around 11 degrees and only one brug showed cold weather damage. The peppers and tomatoes, petunias and other brugs are fine. The garage only stays a very few degrees warmer than the outdoor temps, but even when temps have dipped into the single digits, the plants have survived.

For those of you from Central Oklahoma northward, the cold spell might be a bit more brutal. It is still several days away, so it is hard to know just how cold it really will get. However, our real-life weather at our house has been vastly different from our forecast weather the last 4 to 6 weeks. Some nights we've gone 8 or 10 degrees lower than our forecast low and some days we've gone 6 or 8 degrees warmer, so it is hard to put any faith in the forecast at all. In my bones, though, I think we're going to be plenty cold.

Dawn

I have been reading this thread with interest. I have no experience starting seeds or growing in a greenhouse as I don't have mine finished yet. I have used hot and cold frames to start seeds in with good results. My first tomato seeds sprouted in mine around March 1st and weren't planted till around Feb 20th. I know some growers who erect a cold frame inside their greenhouse and say it really helps keep the temps up on cool nights. Like I said I haven't tried that yet but plan too when and if I get the greenhouse finished. I do cover my frames on cold nights and that helps. I have a high/low thermometer. By covering them I noticed an 6-10 degree increase in the low temp over not covering one. Jay

I hope you have success and let us know how things turn out.

I am just a beginner also, as most of my success/failure is trial and error.

One big failure was with celery. i had beautiful plants in containers in the greenhouse, but they were drying out too fast during the day while i was gone. I had the bright idea of setting them inside a feed tub under the benchs. they stayed moist,tooo moist. when i watered them they did not get the air flow to dry the stalks and rotted after awhile.

I'll try to get some pictures of my greenhouses and post them. pictures are better then me explaining.

I'm in the process of getting dsl at work and hopefully i can upload the pictures faster then this dialup. should have it by next week.

I have an unheated greenhouse and have successfully overwintered a number of potted plants which sit on heat pads and are under blankets that I made from bubble wrap. Even when it is in the teens outside, i can keep the soil at about 45-55 degrees, and right now I am growing onion and lettuce seedlings in it. I am in eastern max, zone 6B.