mull-
I start my seeds in my greenhouse in late-March when it can still get down to freezing at night. However, I have electricity in my greenhouse, and I have my seedling trays on heat mats and under propagation domes, so they remain unfazed. If you can get electricity run to your greenhouse, it will make a big difference. Large heating mats -- big enough for 4 standard trays -- only use about as much energy as a 100 watt bulb. It's also important to use a thermostat with the mats so the plants don't get cooked.

Hi Mull,

Cool, we are nearly neighbors! :)
Our greenhouse stays pretty warm at night. I think it's pretty well frost free by late March/early April. I can usually expect the low temp in the GH to be 5-10 degrees warmer than the low temp outside. Ours is pretty well insulated (8mm twinwall polycarbonate) and we have a nicely insulated foundation. Plus it is chock full of black water buckets.

If you use the heat mats in your greenhouse you'll be fine - that is, if you have electricity in your greenhouse.

Here's a list of a few things I do to keep things warm in the spring:

- put flats on the shelves during the day (warmer there)
- move flats onto the floor at night (warmer there)
- use plastic domes over the flats and then cover the the whole thing with frost blankets. That will almost always be 10 degrees warmer than the outside low temp.
- If it is really cold you can put your flats on the floor near a couple of black water buckets and put the blankets over both the buckets and the flats. Cozy!
- take off the plastic domes during the day, unless it is really cold AND cloudy. I have cooked more plants this way!

- For the heat mats, I put a couple of sheets of styrofoam underneath the heat mat because otherwise much of that heat is lost through the bottom of the shelf.
- When all else fails, bring the flats inside at night. If I do this I try to limit myself to 1-2 flats because that gets old after a while.

Hope that helps!
Karin

Karin-
Great point about the styrofoam. I forgot to mention that I also have my heating mats on 3/4" styrofoam sheets, and it works well, definitely saving a lot of electric energy.

Thanks for the great ideas...any chance you guys have one more? I don't have heat to my greenhouse and it isn't really practical to tie in from my house at this point. Is there a way to get a extension cord in during those cold months without letting all the cold air in?

mull-
First, of course, only use a heavy duty cord that is rated for outdoor use. Any kind of extension cord is only supposed to be used on a "temporary basis" according to code, so don't let this become a permanent situation by default. Also, do what is necessary to give the cord protection from accidental damage. Finally, don't overload it, especially if it's a long run.

Now, having warned you, what is your greenhouse like? Does it have plastic glazing? If so, drill a hole big enough to accommodate the plug end, or cut off a small piece of a corner. After you pass the cord through, you can patch/caulk it to seal the little hole from air leaks. Does that work?

Hmm, that's an interesting idea! I like Kudzu's recommendations though. But I guess if it were me I would skip the heat mats and just start the warm weather plants indoors and move them out as soon as possible. I think we're talking about a pretty narrow window of time, right? If you want to start your tomato seeds in late March/early April, then it's not that long until the greenhouse ought to be warm enough to not freeze at night. And at that point you can move everything out to the greenhouse.

Do you have a wireless thermometer in there so you can see the temperature during different times of the day? That's a key thing to do so you can learn what to expect from your greenhouse during different types of weather. Then you'll be able to look at the weather forecast and know when things inside the GH may be in trouble.

I think I am with Karin on the starting inside business...I already suggested drilling a hole in the greenhouse to my hubby who about fell over:). He has hours and hours of work into that thing and isn't about to go for that.

I do have a wireless thermometer and was a little disappointed by the amount the greenhouse cools off at night, nearly to the same as the outside temperature. It does warm up very quickly though once the sun comes back out. I have been reading about the passive solar heat and thinking about putting some black barrels out there. Does it seem to make much of a difference? I am a little hesitant to fill up the space with the barrels because all my beds are ground beds and I would lose space that way.

mull-
Try it indoors...however, I predict in your situation that you would have much better results if you used your greenhouse for the purpose intended and had electricity. I started my seeds 2 months ago, and where I live it won't be safe to put out tomatoes for another 2 weeks. They are much faster growing and sturdier being in the greenhouse. I'm a little perplexed over why your husband would have a heart attack over one very small, neatly placed hole...but maybe he'll soften up next year when you want to get full use out of your greenhouse! Lastly, while passive heat can help a bit, it won't make a huge enough difference to be worth it for you. I wouldn't want to lose any space in my greenhouse with barrels. The no-lost-space, easy alternative is always going to be electricity.

I had a thought about the extension cord - could you dig a hole underneath the foundation and basically tunnel it inside the greenhouse?

But kudzu is right, having electricity opens up a lot of options. Such as listening to nice music while starting seeds. :)

Did you guys connect right to your house supply before you built? I agree that electricity would be really helpful, but our greenhouse is quite a ways from our house and the outlet we would have to use is outside...probably not a great set up.

I started looking into stand alone power sources (solar, battery with an inverter...) but that is getting quite a bit out of my comfort zone so I think next year I may try some plants inside and some outside with as much physical protection as I can figure out and compare the two results. Have either of you tried the bubble wrap around the walls or anything along those lines? Maybe not, given that you have electricity.

Thanks kudzu for the opinion about the water barrels. I have gone back and forth on that. I'll just continue on without those for now.

We had electricity and water put in right after the GH was built. Of course ours is right next to the house so it was easy.

I haven't tried bubble wrap but lots of people have. If you search around this forum for that you'll get some more info. Same goes for water buckets/barrels.

I like your idea of trying some seeds both ways. Ultimately we all figure out the best plan for our conditions and I'm sure you will too!

mull-
The bubble wrap would help retain heat, and its something that doesn't steal any room away. It's like having an extra layer of glazing. Also, this forum has lots of old threads about alternative heating, like solar cells, and that's an expensive thing to do that would also be too much trouble for you. Some people also use ventless propane heaters if they don't have electricity, which can work. However, I prefer the ease of heat provided by electricity and controlled precisely by a thermostat. If you check out the link below, you can read some of the GW posts about heating and heaters.

[I should also mention that karin's suggestion about running the cord under the foundation -- while clever -- is not a good solution since you don't want to be burying any part of an extension cord in the dirt or have it some place where it is in a puddle of water as that can pose a shock hazard if there is any failure in cord jacket. My wiring is underground, running from my house to the greenhouse, but I enclosed it in plastic conduit and used the required wires that are rated for this use.]

Here is a link that might be useful: Ventless heater

I just finished my greenhouse and now I am researching/experimenting what I can grow and when. I printed off the timing post from Karin in Montana because I also live in Montana (officially in Zone 5 but really more like Zone 3 - 15F on May 15 this past spring!!). Temps are still in the 90's here but I've managed to limit the high temps in the GH to about 6-8 degrees higher than the outside temp with a misting system and solar operated fan. I just planted pelleted carrot seeds in the hope that I can germinate them with soil temps in a raised bed around 80-85F (fresh carrots in November!?). Also plan to try and grow lettuce, spinach, swiss chard and Asian bekana greens as soon as the temps moderate a bit.

Hi Danr,

What a handsome greenhouse that is! It looks especially sturdy which will come in handy around here. And yes, I can tell by the backdrop that you are also from MT. :)

It sounds like you are off to a great start if you have been able to keep your greenhouse cool in this hot summer. I very nearly bought one of those solar fans but I opted not to in the end. How do you like yours? I love the solar-powered idea.

Your seed starting plans sound spot on to me. I am just getting lettuces going again. I planted them in windowboxes which I put on the floor where they get misted on from above. They sure do like that. It's hard to get them going this time of year but I think we are close to the Big Cooldown. You'll be able to have those greens all through the fall and maybe some will even overwinter for you.

I'm going to hold off on my carrots for another week or two. I just harvested all the carrots out of the greenhouse over the weekend and I got a huge haul of 15 lbs. Those were seeded Sept 1 last fall, and I've been pulling out a couple pounds at a time all through the summer. But now I took them all out because it's getting crowded. I agree that the pelleted seeds are the way to go. Your soil temp is really 80 degrees? That's much warmer than I'd expect, the way things cool down at night.

Good luck and keep us posted!
Karin

Karin,

So far, the solar fan is working fine. It has a thermostat switch that kicks in when the GH temp reaches 85F. I have two 18x18 louvered vents along the floor on the west side of the GH and the fan is powerful enough to open those vents but not fully. If I have any complaint about the fan it would be its limited pulling power. It is a critical component of my cooling system (the misting system along with the air exchange lowers the temp) and a lot cheaper than running 150' of electrical line!

I am really looking forward to figuring out what will grow when in my new greenhouse. Again, having your original post gives me a great starting point.

The weather forecast looks good for later this week and next - highs in the low 80's instead of upper 90's. I am running out of non-bolting lettuce and need to start more but its been too hot!

Dan

Hi Dan,

In the absence of an electrical line, your solar fan sounds like an ideal solution. Nice work!

If you still have any non-bolting lettuce you are doing very well. What kind did you grow?

I managed to get the next crop of lettuce up and running. I started the seeds in the house where it's cooler, then kept them in the shade for a week or two, then transplanted them both inside and outside. I'm keeping them under shade cloth and misting them once or twice a day. They seem to be over the hump and look like they'll make it now. In the meantime, we've been having "lettuceless" salads with cucumbers, sweet peppers, carrots and cherry tomatoes. Yum.

36 degrees tonight! I imagine you will have a similarly chilly night. Aren't we glad we have greenhouses! :)

Karin,

34F predicted for us tonight. I have everything covered - nothing in the new greenhouse yet except some carrot seeds I started in the raised bed.

The two lettuce varieties I am still harvesting are Crisp Mint (which is a romaine) and Red Summer Crisp. The Crisp Mint has just bolted but I am hanging on to a few plants of Summer Crisp but it too is starting to show its age.

It's been a great year for tomatoes (compared to the past two years). I typically grow the 60-65 day varieties - Polbig and Rocky Mountain are doing very well for me this year. I am looking forward to growing a longer variety tomato in the greenhouse next year. How many extra tomato growing days do you think I might gain in the greenhouse based on your experience?

Dan

Hi Dan,

I had good luck with summer crisp lettuce too. That was the longest-lasting type we had this summer. I can't remember the variety we had offhand, but it was durable and super crispy, almost like iceberg lettuce.

Those sound like good tomato varieties - I will have to look into them. The greenhouse must add 45-60 extra non-freezing days - it's really a lot! (all of April and most of October stay above freezing.) I still go for the early tomato varieties though because I'm impatient. My best early tomatoes have been Matina and Early Wonder. Matina did not enjoy life in the greenhouse because the misting created spots on the skin. Otherwise it was healthy and crazy productive though. They both do well outdoors here as long as they are in a warm, protected spot.

This year I have 'Goliath' growing in the greenhouse as a longer-season more beefsteak-type tomato. It is wonderfully tasty but it cracks and is very watery. So I'm not sure it's the Perfect Tomato I am always seeking. :)

Karin,
I will have to check out Matina and Early Wonder. I too am searching for the Perfect Tomato. Polbig is at the top of my list right now but I'm always ready to try a new variety.

Tomato cracking is another gardening mystery I haven't quite figured out. Last year all my tomato varieties cracked badly toward toward the end of the season. This year I decided to change my watering schedule and wait for visible signs of wilting before I watered. That translated into a lot less watering this year compared to last. No cracks this year - growing the same varieties. I'm not sure I have it figured out but its another data set in a lifetime trial!

Hi Dan,

How does Polbig taste? I just looked it up and Johnny's describes it as "good tasting" which is an adjective I usually avoid. I go for the ones with more impressive descriptions. :)

I'm happy to report that the new lettuce crop is off and running. We've had salads the past two nights. I'm in heaven with salads this time of year, with Buttercrunch lettuce, cherry tomatoes (Sweet Baby Girl), cucumbers (Diva), carrots (Nelson), and sweet peppers (Gypsy). These are all the most reliable, yummy vegetables I've come across and I grow them year after year. They are like old friends.

Thanks for the watering tip. I will hold back the water on Goliath. Its neighbor, San Marzano, is extra thirsty and suffers from blossom end rot. But I will just water the San Marzano and skip the Goliath. Do your tomatoes get blossom end rot and if so, have you figured out a cure?

I need to start bok choi, spinach and arugula today. Soon it will be time for those heartier fall greens. I love how the different types of veggies change with the seasons. I find it endlessly fun (and tasty)!

Karin,

Polbig's taste is on par with all the other early season tomatoes I've tried. I grew up in PA, so none of them taste like a good old-fashioned beefstake! I'm still searching for the early variety that tastes great.

I have had blossom end rot in past years but this year only a few fruits were affected. I think watering (how much and when) is still the hardest part of gardening.

Yes, I agree, finding the beefsteak flavor in a 60 day tomato is the holy grail, isn't it? Matina has a lovely flavor, but the tomatoes are small so you can't build a sandwich out of big ol' slabs of tomato.

I can report that Silvery Fir Tree, Beaverlodge Plum and (of course) Early Girl do not have that true tomato taste - not worth a spot in my greenhouse!

Blossom end rot is an ongoing problem for Roma-type tomatoes and being inside seems to exacerbate it. I will keep on experimenting. By the end of the season, I have never complained of a shortage of tomatoes though, so it's not exactly a crisis. :)

Two hard freezes here this week ended a very good tomato/basil/pepper year. Unfortunately, all that hot and dry weather spawned the fires we are enduring. I rushed a few potted annuals ino the greenhouse before the freeze and now they greet me every day in their mid/summer best. I love it!! Another bonus of the cool nights - my strawberries are back in limited production.

Wow, it got cold enough there to wipe out your tender plants? Bummer. Especially now that it's warm again.

I was out of town for the freeze but my dutiful husband got everything covered. Our outdoor tomatoes, peppers and basil are all in spots that are either covered or sheltered, so it's easy. Good for you to get your potted annuals in the greenhouse where they will last a good deal longer.

I enjoyed lots of harvesting today, which feels proper this time of year. I'm impressed you have some strawberries coming along. That is one thing I have not really been able to grow well.

Are your greenhouse carrots coming along OK? I plan to start some tomorrow.

I too had everything covered but it got down to 26F. I live near the river bottom so our low temps are often 3-5 degrees lower than the surrounding area. This is why I built the greenhouse!

My carrots are looking good. They've been in the raised bed inside the greenhouse for four weeks. I also planted lettuce and swiss chard in the GH raised bed. They are also looking good but I noticed that the lettuce I sowed directly in the GH two weeks ago has caught up to the lettuce I started indoors a month ago and transplanted. Do you have any problems transplanting lettuce seedlings?

Well, you are very smart to have a greenhouse then, since you will always get the cold end of cold snaps.

Transplanted lettuce seedlings seem to need some intensive care to get on their feet. Especially when I wind up with several plants per cell in their 6-packs and I tend to break them apart into individual plants. This sets them back a lot and I probably should stop doing that. I pamper the transplants with occasional misting with water and I keep them under a row cover to give them shade. They really appreciate this special treatment.

Despite the needed TLC, seeding them in 6 packs is still easier for me than direct seeding and then thinning. But when I grow lettuce in the windowboxes I think it's easier to just sow the seeds directly.

This 3-tier seed starter purchased at Gardening Supply Company worked great this year to start our seedlings indoors before moving them out into the Greenhouse - and much less expensive than heating the GH in our climate. We started the Tomatoes in February indoors and saved substantially on the cost of the plants when compared to purchasing starts at a local nursery. We had ripe tomatoes in June and are still harvesting them.

Karin, So far my greenhouse is staying about ten degrees warmer than the outside temp (that's without sun which is standard wintertime fare around here). I am harvesting a few varieties of lettuce and swiss chard regularly. The carrots are a week or so from being ready - they may not add much growth given the soil temp inside the GH. They are predicting arctic air by the weekend. That might be the first big test.

Thanks for the pic Dan, it looks lovely in there!
I am watching this weekend's weather too. I still have tomatoes and cukes growing! Not much longer though.

Looks like you can cover things in your raised bed and you will soon see how you can nurse things through the cold temps.

Your petunia basket (wow is that huge and happy) may not be too happy by this weekend though. :(

Hi Karin! I am starting to think about spring and my first season with a greenhouse. I usually start my seeds indoors under grow lights but I am thinking about using the greenhouse to start all of my seeds. I can run an extension cord (this summer I am running electricity to the greenhouse!) to connect a 4' seedling long heating pad. I'm not worried about the temps as much as I am the light. Do you think my greenhouse will provide seedlings enough light to keep them from getting leggy? Indoors I have a system where I can raise and lower the light fixtures - I keep the lights within an inch or two of the seedlings as they grow.

Hi Dan,

Exciting to be thinking of seedlings again!
For sure the greenhouse will be light enough - it will be a lot brighter in there than grow lights.

The temps are harder but it sounds like you've got that under control. When are you thinking of getting things started?

I may be overconfident in the temperature control department. Today I had 86F in the GH and 35 outside! I didn't have the fan on however - I will be counting on outside air ventilation to keep the highs under control. Do you start any seeds in the GH?

I will be in Hawaii until Feb 22 and plan on starting some seeds soon after I get back. I'll be paying close attention to your timetable that started this thread.

Hi Dan,

I start nearly all my seeds in the GH. Sometimes I germinate them in the kitchen because it's warm but as soon as they germinate they go to the GH for the sake of good light.

For temperature regulation I stay pretty busy making adjustments during the day. Clear plastic covers on, then off when the sun comes out, then on again in the evening, then flats on the floor covered with a blanket at night, etc. It's not a passive method. But I like the routine of visiting the greenhouse during the day, especially in late winter when it is the only place around that is warm and green.

Late Feb sounds right to me, for the cold-tolerant plants. I am getting lulled by the warm weather we're having now, but I will wait until late Feb before I start up again.

Hawaii - nice! Have fun!

Karin, Happy spring (-like weather)! I noted you start basil that you intend to grow inside the greenhouse in mid-March. My greenhouse is definitely getting warm enough during the day to make basil happy but I am guessing there will be some nights inside the GH when the temps are 35F or so. I'm wondering how you protect young basil starts during the inevitable cool nights when greenhouse temp are in the 30s?

Hi Dan,

Hmm, interesting to look at the list I originally posted here because this year I am going to wait one more week, for the reason you mentioned. It was 31 in my GH this morning.

That said, it's not too hard to keep things warmer at night by putting the flats on the floor and covering them with a frost blanket. A seedling heat mat would easily do the trick too.

Worst case you can always bring the flats inside if its going to get really cold.

Happy planting!
Karin

Very informative long-lived thread. GH gets built this year after nearly forty years living & gardening at the same address. Been studying Eliot Coleman's The Winter Harvest Handbook like I used to cram for final exams. He advocates the lightest row cover, Agribon 15, for continuous winter cover except for when they are harvesting during the warm part of the day. He is Zn 5 in Maine and harvests year round from mostly unheated or some minimally heated GH's (adds just enough heat to keep them above freezing.) He's tested using heavier material but found it didn't work as well because it prevented the ground from heating up during the day. Light weight covers get enough frozen condensate on the underside to mimic heavier cloth and reflect the radiated heat back into the plants at night. He does a lot of experimenting and is gracious in sharing the results.
I plan to supplement the heat for my GH from the wood stove in my shop. The GH will be attached to the SE side of the shop and there is a door that will open into the GH. I intend to put a fan in the doorway and blow heat into the shop during the day and out of the shop at night when I have a fire going. The shop is very well insulated and requires only one fire every day or two to keep it from freezing in there. Hope it works.
Karin, your original post is wonderful. A great resource for guys like me. Thank You!
The link is to my newly designed website, complete with several blogs, one being for my gardening. I live in Lively, hence the punny name.

Here is a link that might be useful: Lively Dirt - The Garden Blog

Lively, I can tell you are going to have a great time with your greenhouse. I think that a science or engineering background really helps, as the whole thing reminds me of a big science fair project. Keep us posted as you finalize your plans.

Karin

Karin,
I would appreciate if you could show some pics of your beds, and how you are using the fabric to warm them.
Papa Jamie

Hi Karin! Happy spring (almost). I started my greenhouse raised beds last week. It was a cold and sunless Feb so my plans to start the greenhouse bed early were foiled once again by Montana weather. I have lettuce, radishes and spinach up but no sign of life yet from the carrots or kale. I ran electricity to my greenhouse last spring after my last post and now have a heavy duty fan on a thermostat that kicks in when the GH temp reaches 80F. It has made a huge difference in managing the hot temps in the summer. I grew longer season tomatoes and peppers inside the greenhouse without a problem. Except for the aphids I battled all summer and fall! I am pretty sure they were came in on some plants I bought from commercial greenhouse.I will be very careful in the future with anything I don't grow from seed. Live and learn. I also added a shade cloth to the south facing glazing because I had some problems with delicate seedllngs frying in the hot sun while I was away at work. I used 70% shade cloth that I can remove later in the year. How is it going in your part of the state?

Hi Papa Jamie,

Here is a pic of the lettuce blanket. Basically it's metal hoops spaced every 3 feet or so, then blankets draped over the hoops. I've had great luck growing things in window boxes, because they are portable. So the window boxes go on the floor, covered with the blankets. When it was really cold this winter, I put about 4 layers of blankets over everything. Must've worked because all the boxes survived.

Dan! Hello to you too.
I just got my first seeds started today. I should have started earlier, but winter is very full with skiing, so time and energy are rare things to have! Nonetheless, I had a wonderful morning of getting things underway. Cleaning the greenhouse has got to be one of the best-feeling chores ever.

I agree that frying seedlings is a major hazard. It can get insanely hot, even this time of year. I have found that the plastic domes that cover the seed-starting trays can be really hazardous. Luckily I work from home so I can keep an eye on things. We use 50% shade cloth plus a misting system and fan, and that's worked well for us.

I battle aphids too. I noticed that ants "farm" them so I use borax-based ant traps in the GH and that helps a lot. Also, there are some plants that aphids love so much (spinach) that it's just not worth it to grow it in the GH.

I hope you get everything off to a good start!

Another pic of the blankets and the beds. And the daffodils! They are always a treat when everything outside is still all snowy.

I like the idea of the daffodils in the GH. I will throw some in next fall. I also read about the ant/aphid symbiosis. I placed the same ant traps as you described around the outside of the GH. It didn't seem to help that much. I went through a lot of neem oil last summer. I am hoping the 20 below zero temps we had this winter killed every last one of them inside my GH!

Try the ant traps inside the GH. I don't think cold weather bothers them too much, since they seem to be here every summer regardless.

Karin - you did post photos of your GH/plants - somehow I missed it. Your lettuce is looking good - as always! What do your tomato plants look like? When do you plan to plant them in your GH this year?

No tomato plants quite yet Hudson. I'll get them started very soon. Actually, I am still seeking some new sauce-type tomato types, I've been reading about some with resistance to blossom end rot. We'll see.

These last few winters I am always a little late getting started in the spring. You are much more on top of it that I am! (but your photos and prompting do help shoo me along...)

Karin,

I have had consistenty good luck with Bellstar - a short season determinate sauce variety. It looks a little suspect early in the year and then produces like crazy. I will be trying the Heinz variety from Territorial Seeds this year as well.

Thank you for posting the pics, Karin. That really helps. My brain likes pictures, and now I get what you are doing. I have never used anything like this in my GH, so I guess I better get my little woman to start doing some sewing. Thanks for all the great tips on here.

No need for sewing Papa Jamie. You can just cut them to size and they don't fray or anything. So your little woman is off the hook!

Hi Karin,

I was reviewing your last posts on aphids in the greenhouse because I just discovered the first aphids of the season. 8(

Last year I had an aphid epidemic and was never really successful in controlling them with neem and insecticidal soap. The difference this year is that I placed my Terro ant traps out early and I have no ants in the GH yet. It will be interesting to see if the ant-aphid relationship makes a difference for me. Last year I had lots of both. I have also moved the culprit plant (early Jalapeño pepper) out of my greenhouse. After last year's experience, I will sacrifice a couple of plants if it saves me some aphid headaches!

Its been a cool spring here in Stevensville but everything is coming along nicely now. Hope all is growing well for you.

Dan