Update: I have since moved from this house and built a new harbor freight greenhouse with even better upgrades. I’ll include a post of this newer greenhouse soon! this post may contain affiliate links click here for more info.
Is there anything better than walking into a warm, humid greenhouse? The smell of moist potting soil, plant foliage, and flowers all concentrated together has got to be one of the most therapeutic experiences. Like walking barefoot in the sand or eating some really good chocolate. In high school and college I worked at the most beautiful garden center attached to an enormous greenhouse that doubled as an event center. When I walked into that greenhouse I would feel weight and worry from the day evaporate as I walked past the ferns and just breathed in the smell of everything living.
I think many garden lovers, especially those in climates with a full four seasons, fantasize about starting tomatoes in February, getting a head start on growing annual patio pots, and overwintering lemon trees. Building a greenhouse was at the top of my yard to do list when we purchased our home three years ago. It got bumped down the list a bit in favor of things like laying new sod, building a fence, and purchasing plants to serve as the foundation of our landscape. But last spring we looked at our to do list and found greenhouse construction right up at the top. My first choice, a custom glasshouse imported for England for a mere $17,000 was more than a bit out of reach. As I researched different companies and kits I found that for my price range, if I wanted something beautiful it would have to be tiny, and if I wanted something with enough space it would be plain and ugly. I decided for the most price friendly greenhouse for its size, the Harbor Frieght 10’ X 12’.
Making the decision to purchase this greenhouse meant factoring in a bunch of greenhouse improvements to our budget. As silly as it may sound, having a greenhouse that was equal in beauty and function was the goal. I knew my greenhouse would serve as another outdoor room in my garden, and I wanted it to be an escape.
I’d read plenty of negative reviews for this greenhouse. I was aware that the aluminum frame would need some sturdying up, and that the panels would require some work to keep them from blowing out in windstorms. However I felt that for the price, around $500 after a sale + coupon, I could make it work perfectly for our space.
Major Upgrades We Knew We’d Want
- electrical
- ventilation
- automated watering/humidity control
- benches and storage for plants
- potting/work area with a sink
The Eletrical
We were able to add a light fixture and two outlets to the greenhouse. Sometimes I’ll go out in the greenhouse after the girls have gone to bed, flip on the light and do some transplanting. The outlets are a means for us to use the ventilation system we came up with, as well as plug in our seed heating mats or space heaters if we have a chilly night in late spring. The metal conduit through which we ran wires for our ceiling light help add stability to the aluminum frame.
Ventilation
The greenhouse came with four of the roof panels opening as vents. Greenhouse ventilation is important because temperatures in the greenhouse far exceed the outside temperatures during the summer months due to the warm air that gets trapped inside. Although having these events open would allow for some air movement, in order to keep the temperature at a more hospitable range we knew we needed a more aggressive approach to air circulation. We invested in outlet thermostat that can be set for both a high temperature and low temperature range. We have ours set so that at 85°, the outlet turns on the ventilation fan And outlet turns off when the temperature gets down to 80°. This fan pulls warm air from inside the greenhouse outside, it has louvers on the exterior that only open if the fan is running. To allow for fresh air to circulate through the greenhouse we added an opening with louvers across from the ventilation fan, so that when it runs it can pull air from the outside. During the summer months we will hear the fan turning off and on throughout the day as it works to keep the greenhouse in or acceptable temperature range of about 85°.
The thermostat we have has two outlets, one for the fan and one for a heater. I don’t heat my greenhouse through the whole winter. I usually start heating it early to mid March once I have some of my seedlings out there. With this thermostat my heater will kick on when my greenhouse drops below 45, and turn off when the greenhouse is at 50.
Links:
Automated Watering
We purchased and hooked up an automated misting system to ensure that our greenhouse had high enough humidity levels and didn’t simply turn into a desert. We can tell our Mister how often to turn on and for what duration of time. During the hottest summer months I set my misting system to run every 10 minutes for 30 seconds. That kept our humidity up and also helped lower the temperature along with our fan.
Benches
I wanted to be able to utilize as much space as possible, so my husband constructed benches to run down each side of the greenhouse, with hardware cloth for the top level, and 1″ x 3″ slats for the bottom level. The benches are 2″ wide leaving plenty of space in the center of the greenhouse for a removable island when we need extra space, or a table and chairs for our girls’ tea parties.
Potting/Work Area with Sink
This might be my favorite part of the greenhouse. Having a solid work area where I could put down seeds and divide plants was really important. I also wanted to be able to rinse my garden tools, wash my hands, and fill up watering cans. We found our impossibly deep cast iron sink at our local restore, and we used plywood and 2 x 4’s along with our extra hardware cloth make a mold for a concrete counter top. The counter top supports an old, mirrored hutch that we found a secondhand store. I love having the two big mirrors reflecting the greenhouse and the rest of my garden.
Extras
One of the things we kept reading about the Harbor Freight greenhouse was that the panels would blow out in strong wind storms. Reviewers said that the clips holding the panels in work very effective, and that purchasing additional clips was a good option. Instead of adding more clips we ended up using self tapping screws to secure each panel to the frame.
This is so much great information! I haven’t bought a greenhouse for some of the same reasons you described. I am going to look in to this greenhouse. Thank you for all the great information on how to upgrade it!
I just got the 10+12 Harbor Freight . I’ve had the smaller one for 4 years. The first wend storm we had ,right after we built it, 3 of the vent panels blew off and one of the doors🤨 so we Used the self tapping screws and also we put between each window an aluminum bar across each of the windows and on the vents. It made a difference. Can you tell me Where did you get your fan?
I believe you are located in Utah. How do you keep your greenhouse warm in the winter? Thanks
We’ve actually been experimenting with thermal mass heating by filling up black containers with water. The idea is the sun will heat the water in the containers, and that the container will radiate heat as the water cools back down. This method has kept things like Spanish Lavender and Draceana spikes and a few varieties of succulents alive through the winter. However, the plants have to be very close to the black containers of water. I’m sure if my greenhouse was smaller, or better insulated this method would work better. I’ll be trying something different next winter. I’d like to be able to keep my greenhouse warm enough to overwinter more tropical plants like bougainvillea and citrus patio trees, ideally 45 degrees or more which sounds difficult and pricey in my climate. But I’ll be working on that and post an update!
I’m in central NC and some nights get cold. 28/23 this week. I use Black metal barrels filled with mulch that I dampen weekly. The days sun heats it up to dissipate at night. I have them on the corners and in the center. I also put landscape fabric on the floor/paths, filled with mulch and then topped with flagstone. Both collect and hold temperatures. Below 30 degrees, I use a propane tank with an eye burner on top and a window fan behind the heater. Both on low. It keeps everything above 40 until the sun shines!
Those area all great ideas. I’m definitely interested in trying to utilize some mulch/compost heat in mine. Because of the size I struggle to heat it during December-February. Last week we got down to 3 degrees and I was pleasantly surprised to find my winter lettuce in the green house had survived the night.
Where did you get your fan? Love what you ve done! ThNks for sharing!
Thanks! We just ordered a 14″ attic fan with louvers off Amazon and attached a plug that we could plug into our thermostat.
We’ve had this greenhouse for about 2 years. Unfortunately the panels are not UV protected. They are now disintegrating and must be replaced. The replacement cost is more than the original cost of the greenhouse from harbor freight.
Just a warning!
We noticed a ton a reviews with this same complaint in our greenhouse research. We’ve coated our greenhouse with the 303 Aerospace UV Protectant. We’re hoping a yearly application will extend the life of the panels a little longer. We’ll plan on replacing the panels a couple at a time to make it more affordable.
Can you give me more detail on how you installed the conduit to run end to end? I just finished my construction, have done all the same but the ceiling pipe for wiring and the mist system, btw where did you get that?
I love all your ideas. Hope to put one together this summer.
Thanks for all the information. Hope to hear more improvement later.
Although helpful, I came to read your blog to get some particulars about the additions you’ve made. Like, specifically what size ventilation fan you chose? and how you went about installing it? & how’d you add running water? etc…what misting system did you choose? how much did the extras cost? That type of information would be very helpful to me after building this greenhouse in 2022. Maybe you’ll come back to post some additional information that will help the next person to visit your blog looking for particulars…If not, oh well, your girls are adorable!
I tried misting but found everything covered in mold after a couple of days, how do you keep this from happening? My husband secured this greenhouse very well. We really could not figure out how to use the things which came with the kit to secure the panels so he just screwed them in and we have been fine for well over a year. Will look into the coating for UV Protectant as we are in a very hot climate. I am going to pass this on to my husband to do some upgrades because we need electric installed and not running from an extension (LOL!!!), and I would love to have a sink! We have done a bit of hydroponic gardening as well, and it was probably the best out of everything, but I absolutely love, love, love my greenhouse! Now to get it cleaned out! LOL!!!
The best way to combat mold is to always have some air moving. Because my vent fan is used to control the temperature in the greenhouse it isn’t always on. I usually have a small fan that stays on to circulate air.
Thank you, I will certainly try that although I was pretty sure we had a fan on.
Last winter we had quite a snow storm in New York! And the roof collapsed, couldn’t hold the wet snow. Now my harbor freight green house got a 2×4 skeleton frame inside the harbor freight green house to hold up the new wooden roof trusses. We bought clear plastic corrugated roof panels for the new roof and made the roof vents where the old ones were. By adding the 2×4 skeleton I can now add shelves in the green house. Love my little green house. Got a heater and going to try to keep those tomatoes and peppers growing into fall! 😊
I’m so glad you were able to save your greenhouse! I’m hoping to keep my tomatoes going too, especially here where we’ll drop into the 40’s next week but still have highs in the 80’s.
Are there sketches/plans available for your bench design? We were just given an extruded aluminum G.H. free for the moving. Just putting the finishing touches on it now but have to build some benches. We installed a solar powered fan (Amtraksolar.com) and it is working fine but is bare bones and will need to be regulated. It’s a 50 watt fan and the panel we chose is 100 watts so I will be able to charge a battery to extend fan usage during low light conditions. It has been a journey.
A solar fan is a great addition! I’d like to upgrade mine to solar because during summer months the fan works pretty hard to keep temps down in my greenhouse. I don’t have plans for this bench design. I’ve since moved and build another harbor freight greenhouse with a different bench design. I’ll be doing a post on the updates here soon. But I can tell you I created my benches to be counter height at 36″ tall and 24″ deep to accommodate standard nursery flats with a little extra room. I also have a lower shelf 8″ from the ground. My benches are made with 4×4 legs with 2×4 supports. The tops of my benches are 1/2″ galvanized steel welded wire. I hope this helps! If you’d like more details check back soon for an updated post about my second greenhouse!
Any tips for us beginners that bought a simple plastic greenhouse. The one with zipper door and roll up windows. Ideas for more ventilation and heating in winter. Also placement in my yard. I got zero yield from it this year. Very disappointed.
I’d say any greenhouse is a step in the right direction and a great investment in your garden, no matter how simple or fancy. I’d definitely start with getting some king of thermostat you can monitor through your phone to check on temps without walking out there. I’d get a fan to circulate air and a space heater for cooler months. Depending on your location and how cold you get you can also line the interior with clear bubble wrap for extra insulation. I’m in zone 7b and I don’t even try to heat my greenhouse mid November-February because it’s just too difficult and expensive. Monitor your temperatures in spring and fall and roll up those windows with the fan on to keep things from burning.
I purchased black storage tubs with black lids 2. My green house is 8′ x 6′. I use the containers for composting as it creates heat as well as much needed rich soil. Poke holes in lids. They work great for me!
That’s a great idea! Thanks for sharing.
This was very helpful!
So happy to help!