Seed starting greenhouse

I'm currently working on converting this greenhouse into a seed starting green house.

I referred to various image searches to build some shelves. I'm using old cedar boards I had on hand for the frames and some fencing material for the shelf tops.

I'm considering reserving some space for a compost bin to help keep the temperature up in the winter.

I will probably have to get the plastic changed, but I'm going to try to use it as is first.

Any tips, hints, helpful advice welcome. Especially in the vein of "I wish I had known before I started..."

Having trouble posting images, will add more later

Let's try some pictures again

I have found that my greenhouse just isn't warm enough overnight for germinating. If I had electricity in the greenhouse, I would use my seed starting heating mats there, but I don't. So I start my seeds in a building, under lights with heat mats. Then I transplant and move to the greenhouse to finish growing out.

I start tomatoes inside, mid Febuary, maybe 10 weeks bfore official last frost. Then I move them to the greenhouse. If the tmeperature will dip below 40* F I haul them inside. This happens here for a few scattered nights. For the cool weather crops, Again, I start them inside, to speed up the sprouting. I haven't lost anything yet. Once they reach identifiable first leaves, they may stop growing, but are still alive and grow again when it warms back up.

So I guess I should find out what kind of temperatures my greenhouse experiences throughout the year... do you all just manually check with a thermometer? Or do you have some fancy monitoring device?

I do have a raspberry pi I could repurpose... but I'd need to order some sensors and run extension cables... I also don't have power in the greenhouse.

I have a small thermometer in my greenhouse. It does transmit to an app on my phone, but honestly, it doesn't work very well. I have to take my phone to a certain place in my house and refresh it on an app. It's easier just to walk down to the greenhouse. I had a different thermometer that would just display the greenhouse temperature but it broke after about 6 months. The thermometers that I've tried all struggle with the dripping water in the greenhouse and of course they can't be in direct sun, so it's difficult to get an accurate temperature. But I've mostly figured out what the temperature will be like under different conditions depending on outside temperature, wind and cloud cover vs. bright sun.

Got it to a usable state. Finished the basic shelves, patched the worst if the holes in the plastic. Still needs some more improvements and sorting but mostly it needs things growing in it!

So today I got some seeds into some seed trays at last.

Lew Johnson wrote:So I guess I should find out what kind of temperatures my greenhouse experiences throughout the year... do you all just manually check with a thermometer? Or do you have some fancy monitoring device?

I do have a raspberry pi I could repurpose... but I'd need to order some sensors and run extension cables... I also don't have power in the greenhouse.

I monitor my greenhouse with a Temp Stick (no affiliation). It has been game changing.

A lot depends on the temperature.  I had to redo the plastic on my greenhouse this year. I knew it would get to hot so I put in a window in the south and north side.  Unfortunately it's not enough. My little seedlings get fried. I need a solar fan for mine.

Jen Fulkerson wrote:A lot depends on the temperature.  I had to redo the plastic on my greenhouse this year. I knew it would get to hot so I put in a window in the south and north side.  Unfortunately it's not enough. My little seedlings get fried. I need a solar fan for mine.

My greenhouse has a flap connected to a hand crank to open the north side enough to ventilate it entirely. It's easy to get it to cool down. Managing constant temperature though is a lot trickier... It seems like a lot of the farmers around here pretty much leave their greenhouses open in the heat of summer (maybe even at night?) here. This part of Japan is definitely on the hot end of temperate.

Old french technique for heating is to use a corner of greenhouse.  Create a compost pile, as it breaks down it produces heat.

Where are you (what island?) in Japan Lew?

i live in Cape Breton so our climates are probably pretty similar. i have a coupla greenhouses i built out of old windows - you definitely want a window or two installed to vent as others have pointed out - i have the apex of each shed roof as a plastic flap i remove in the summer which helps too... your shelves look pretty good


starting indoors might help you as another pointed out - you COULD also try a trick i use for seedlings earlier than later  which is a smaller greenhouse WITHIN a greenhouse - basically a frame around your shelves with plastic wrap and a big flap on the front... you will have to monitor carefully it will get hot quicker... but the warmth will start earlier, get hotter and if you close the flap at the right time of day... you will trap more warmth longer.. hope these pics show what i mean well enough - cheers!

forgot to add - i use ne of these in the house in like, february to "start before i start" - it is an easier setup than the beast i just posted - they are cheap and oddly reliable - cheers!

https://www.amazon.ca/Greenhouse-Portable-Roll-Up-Plastic-Outdoor/dp/B092MKX2PB/ref=sr_1_14?dchild=1&keywords=greenhouse+stand&qid=1620054075&sr=8-14

Michael Moreken wrote:Old french technique for heating is to use a corner of greenhouse.  Create a compost pile, as it breaks down it produces heat.

It also produces Co2, I believe. This should be another benefit to whatever is being grown in there.

I got some seedlings growing in the greenhouse now. They're pretty leggy, but growing.

I'm using my own soil, full of dormant seeds. After I saw the diversity I had an idea... For managing my seed starting soil - pre-weeding it. If I soak the soil in the tray before I sow my vegetable seeds I can cull everything that grows, then sow my veggies after...

Thanks to all the tips and pointers so far. I am planning a compost pile, a little bit more discriminating than my outdoor heap.

I will avoid including seeds in this one, because I will probably use the resulting compost primarily as a seed-starting medium.

I am trying to make leaf mould in another spot as well, but it's a long-term thing so we'll see how that goes.

Usually with compost piles I hear that they need about 4 feet x 4 feet to really activate. I won't have that much space to work with inside... I wonder if I'll get reasonable results with half those dimensions.

Several asked about my location. I'm in zone 9b or so, so we actually have a year-round growing season. The greenhouse however lets me manage seed starts densely in isolation and I would like to try to grow a few smallish tropical plants in here if I can manage the temperature well enough. My neighbor managed to grow pineapple by bringing it inside in the winter. I'd love to try that. I will probably also just keep a few tomato plants in the greenhouse, most people around here shelter their tomatoes from the rain.

It seems quite dark in there... is there shade cloth on the roof? That would explain the legginess, especially if it’s fairly warm in there.

Kevin Wilson wrote:It seems quite dark in there... is there shade cloth on the roof? That would explain the legginess, especially if it’s fairly warm in there.

Yes. There is a shade cloth. I didn't know that causes the sprouts to try to grow taller... but it makes sense, like they're trying to grow through ground cover to reach the sun.

I intend to remove the shade cloth, but it's also giving some protection from falling branches from the persimmon tree above. I started pruning the tree back heavily this past year. It had grown out to full size, and was basically useless for harvesting from, and was also dropping branches and leaves in inconvenient places. I am waiting to let it recover from the heavy pruning before I have another big go at it, but I'm going to lop off even more big branches in the coming year, hopefully bringing it down to a manageable size. It may not survive... but these persimmons are pretty resilient.

I planned to see how well it worked as-is without removing anything or re-doing the plastic (which will both probably need to be done).

If it turns out that the seedlings aren't capable of transplanting I'll prioritize the re-covering earlier than planned.

I had a bit of time in between work today. Went ahead with building the mini-compost station.

I discovered a useful technique while trying to figure out how to nail it together vertically. You always need something behind what your nailing, otherwise the boards just take the impact and the nails don't get driven in. I found that by using a cut off of 4x4 behind the nail strikes everything came together perfectly.

Ran out of time before I could finish it, but most of the work is done. I just need to put in a middle divider to separate matured from active compost, and some removable front gating of some sort.

I'm giving myself bonus points for burning through huge amounts of my scrap lumber in this greenhouse project. I might actually be able to clear it out soon!

I finally took the shade cloth off the top and sowed another round of seeds after letting the weeds grow and culling them. My okra and tomatoes are leggy, but so far surviving. The basil looks good.

This is pretty much my last chance at sowing for the season. It's about to get really hot.

I'm glad to see things growing in here.

I've been using one of those cheap portable greenhouses you can pick up new for around $70.  I bought it used several years ago and replaced part of the rusted powder-coated pipe with 1/2" conduit and covered it with greenhouse plastic this year.  On last few nights of our cold snap in May, I had no choice but to put an electric heater plugged into a GFCI outlet in there.  Remarkably it worked rather well as I did cover the outside surface of the greenhouse with blankets to try and hold in some of the heat.  While I don't see the electric heater being able to maintain the temperature in a large area, I think if I could perhaps build a smaller greenhouse within a greenhouse and heat that, it would work.

I have been reading and watching Charles Dowding's work and he builds a hot bed and germinates seedlings on top of that.  While that would be great for germinating I'd consider trapping the heat in a temporary structure if I were to try to growing the plants on in cold temperatures.  

Please keep us up to date as I'm planning on building a larger structure this fall and could use all the advice I can get.

Now is the time to start the first round of seeds in the greenhouse (I think).

It's really hard for me to judge when to sow, but the last two years I was way late in sowing everything. So this year I will try the beginning of February.

I'm using coco coir to net the bottom of my seed tray modules. It works very nicely to keep my amalgamation of soil and compost from falling out.



I'm trying to sow celery for the 4th time now... I got it to germinate last time, but failed to get it to grow big enough to plant out. The first two times were complete busts.

I'm also giving strawberry seeds a go. I might not have much success, but it cost me nothing, so I'm okay with that. I sprinkled a few seeds directly where I'm hoping they might grow too, though I doubt any will germinate without babying.



The big bonus of the greenhouse is being able to sow seeds that just won't grow directly sown. I'm really tired of buying green pepper, eggplant, and cucumber seedlings. I'm determined to at least grow them from seed.

I'm sure there is a way to get them to grow directly sown, but I have not had any success yet.

Celery and all the cucurbits including cucumbers are usually described as having delicate roots and not taking well to transplanting. Your cells look small and the plants might have to be disturbed to get them out of it. I start my cucurbits in used 1-liter tetrapak containers. When I transplant them out I can dig a hole, place the tetrapak in the hole, and carefully tear off the container while not disturbing the roots or planting medium. I've had about 100% transplanting success with this method.

My best wintersowed results came from cucumbers and squash.
I wonder if the size of the plants/roots makes the difference, since each of these had a milk jug to itself.
That's roughly 6x6 inches and 4" deep.

Thanks for the tips Rebecca and William!

I'm a total newbie working with a bad youtube education.

I intend to direct sow all the cucurbits too. I'll plant another round in bigger pots or maybe cardboard tubes that won't need much root disturbance to transplant.

I have an abundance of seeds that I need to plant out. Many of them are already dead, but I've been surprised to see quite a few of these 12 year old seeds germinating!!!

Hi L,
Your greenhouse looks terrific. And big enough to start lots of seedlings. Did you add/fill the compost pile? Did/does it give off heat? How is it working? How about the pile of leaves for mold? And how is your ventilation working out for you. Can we have an update?

I've been starting my seeds too. Started all my brassicas on January 1st. Then my hot weather vegies on January 15th. I just started some more a few days ago. I've almost got my little greenhouse full. So far, so good. Everything seems to be germinating in 7-14 days. It's a good thing it's not bigger or I would never stop.

And I had heard lots of people say it is really hard to start strawberry seeds. So over the last few years I started them twice this way. Sprinkled them out on a flat of my mix and then put a sheet of kitchen plastic wrap over them to keep in the humidity, just an inch or so above the dirt. Leave it loose for some air. Worked great both times.

Debbie Ann wrote:Hi L,
Your greenhouse looks terrific. And big enough to start lots of seedlings. Did you add/fill the compost pile? Did/does it give off heat? How is it working? How about the pile of leaves for mold? And how is your ventilation working out for you. Can we have an update?

The compost is full, but I think my green brown balance is a little off. I started turning it regularly about a week ago and covering it with an opened up old soil bag. It was going very slow. It doesn't give off obvious levels of heat, I haven't put a thermo in to check it though. I think it's just a little too small.

The leaves for mold got another big layer after this past year's leaf fall finished. It will be a while before that breaks down.

Managing the temperature in the greenhouse is tricky. It gets extra hot in the daytime but it doesn't retain much of that heat at night. So it still gets just barely down to freezing inside. My toddler likes to go in and leave the door open too... But I'm happy for her to be playing in the dirt! The dew/frost doesn't touch the plants though, so if they're able to take the temperatures they're fine, but I don't think I'd be able to keep pineapple growing in there.

Debbie Ann wrote:
And I had heard lots of people say it is really hard to start strawberry seeds. So over the last few years I started them twice this way. Sprinkled them out on a flat of my mix and then put a sheet of kitchen plastic wrap over them to keep in the humidity, just an inch or so above the dirt. Leave it loose for some air. Worked great both times.

That's great news! This time I'm trying without the plastic wrap, but if it doesn't work I might have a go using some.

My seed starting and transplants are getting better and better. I'm figuring out the timing for sizing up the pots and planting out the seedlings. And also the sunniest spots in the greenhouse where the starts grow the best, since the whole thing is located under the canopy of a big persimmon tree and shaded by the mountain ridge by 3-4 pm every day.

I'm also organizing my greenhouse a bit better. I started taking advantage of the fencing materials that were used to support the walls and hung S hooks to organize my tools and free up the shelf space. I also put in two flowers in hanging pots for a little bit of beautification.  I still have room for improvement, which is the fun of it for me!

Komatsuna mustard, lettuce (sanchu and sunny lettuce), and chinese cabbage starts waiting for space in the garden beds


The sunniest corner, a newly started compost pile, and a new hanging flower basket.


Supplies that need some better sorting, or to be put into use.


Spare pots, trays, modules, a few tomato plants and an aloe vera growing in the center.


Dead vertical space on the back of the door


Getting tools off the shelves and onto dead vertical space!


These tools need some holes drilled in the handles before they can be hung.

I also remembered recently that I had been doing bottom watering before and stopped at some point. Maybe I forgot about it. Maybe I didn't have a free container for water.

I read somewhere that filling a container with water and then putting the whole module tray into the water and letting it soak from the bottom would encourage the roots to develop downward.

Has anyone had any experiences with this kind of watering vs traditional pour onto the soil from the top watering?

I get mixed results with pouring from the top. Sometimes the roots develop all the way to the bottom, sometimes when I go to transplant I barely get any roots with the seedling. Maybe it's more to do with my haphazard potting soil. Maybe I'll do some experiments next season.

Update on how things have progressed with this greenhouse.

Yesterday I finally planted out the last of my starts for the winter garden, so I can start getting ready for spring season seed starting.

I bought two more rolls of greenhouse patching tape and have been mending the holes and tears to keep the temperature and carbon dioxide in and the rain out.

I've also been building the compost pile. Since it's small and I have been working on it for a while I think I'm finally getting somewhere with the compost. I've been keeping the inputs well chopped and easy to move with a shovel. I had too much green, but this past week I added some cardboard, saw dust, and dry wood shavings from wood working. This morning I went in to add some kitchen scraps and when I turned it I could feel the heat coming off the pile! It's hot baby!

I had a huge swarm of fruit flies breeding in the compost for the past week or so, but now that it's getting hot I think it will fry their eggs. I put out an apple cider vinegar trap to see if I could collect some, and it's beginning to work now that the compost pile is heating up. I think I'll be able to get rid of the fruit flies after a while of this. I've run out of mulched spots to continue putting my kitchen scraps in for Ruth Stout style composting for a while, so they're all going to go into this pile until the under mulched compost breaks down again in a month or so. Hopefully by adding some additional wood shavings and maybe cardboard I can keep this pile hot, which will make it SO MUCH more useful! A little heat in the greenhouse should let me keep my tomatoes growing through the winter and maybe even get some pineapples growing as well, which a neighbor said he has managed with some careful attention.

Most especially exciting is that if I can keep it hot I can put in more various inputs that might include some seeds, without worrying as much about having unwanted diversity in my potting soil mix.

This is my third or fourth year of gardening. I've heard that's when things start to really take off, and I think it's holding true for me.

I like it very much.  I have been trying to decide how to do the same thing

Hello You Green House Warriors!

Which direction is your greenhouse oriented? We get really really hot here June-September, so I am thinking of an east facing greenhouse so nothing fries! But, I don't have much experience so, please advise.

Suzette Thib wrote:Hello You Green House Warriors!

Which direction is your greenhouse oriented? We get really really hot here June-September, so I am thinking of an east facing greenhouse so nothing fries! But, I don't have much experience so, please advise.

The standard advice is to orient the ridge/long axis of a greenhouse North-South below 45 degrees latitude, and East-West above 45 degrees.  But, your site and usage will dictate whether this is correct for your specific location.

The rationale for a N-S axis is that things inside get good sun exposure on all sides (again, depending on surroundings).

The rationale for an E-W orientation is that lower sun angles (the not-summer 6 months of the year, more-or-less) the equator-facing glazing will let in more light, and the interior of the other side of the greenhouse can be lined with something reflective to help even out the light on the "back" side of the growies.

My brother and nephew just bought a going-concern hydroponic micro-farm (tomatoes, hot peppers and more). We're north of 45 degrees by a couple of hundred miles, roughly.  That greenhouse is oriented with the ridge N-S.  But, it has a blown double skin, with a wood fired boiler for winter heat.  For this application, the current orientation is probably as good as anything.

In northern climes, some greenhouses are actually shed built, with a low-angle single pitch roof and a glazed south facing wall (sloped or vertical).  Sometimes, end walls will also have partial or full glazing.  Good insulation on all unglazed walls/roof, and thermal mass (IBC totes full of water, thermal mass floor in part) can help to stabilize (even help to annualize) temps.

Caveat: I haven't built mine, yet.