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Are you looking to create a mini greenhouse so that you can enjoy an extended growing season? Here’s how we built one for free and how you can too!
How to Build a Mini Greenhouse for Free
—This post is a collaboration between both my husband and me as I am not so handy with the drill. Enjoy!
We moved into one of our homes at the beginning of October after living in an RV for 6 months. I so missed having a garden this summer and had the urge to plant some seeds and get my hands back in the dirt!
Of course, we were headed into the winter months and that means traditional planting methods were out, but there are plenty of unique gardening methods that would help me get my fix! And yes, I already planted a little lettuce garden in my Aerogarden and I planted an Herb Garden in the kitchen the other day too!
— Learn more about Growing your own Herb Garden!
We didn’t want to spend money on this project though since we have a few more things that we need to focus our extra money on in the house still so we wanted to see if we could build some kind of mini greenhouse for free.
So we dug around our new home and we found scrap wood that the previous owners had left. They also left a few used windows that they were given to make a small greenhouse (but they never got around to it so they left them for us!). So everything we needed to make this cold frame mini greenhouse with only the things we found around our home.
If this is something that you’d like to make, I would encourage you to find things around your own home to use instead of buying something from the store. Or ask a friend if they have any scraps of wood or old windows that they won’t be using. These mini homemade greenhouses take very little for supplies to make them so if you are creative you can find a way to do it with just a few scraps!
–If you are looking to build a little bit bigger greenhouse, you might want to check out this post on Building a Small Greenhouse.
Here is the wood that we gathered. It doesn’t look like much! It was mostly 2x4s with a few 2x8s thrown in. Just enough to put this mini greenhouse DIY project together.
My husband started by measuring the size of the window and made some simple frames by cutting the wood down to size and screwing it together. We made two 2×4 frames and one 2×8 frame because of the wood we had. That made the height of our box about 15 inches.
Then we stacked the frames on top of each other and put together the base of the mini greenhouse.
When you put the frames on top of each other make sure to alternate the boards, this will make it stronger.
Then we cut boards at an angle so that the window on top would be at an angle. This will help to get sunlight to all of the plants and so that we could plant taller plants in the back. Both of these boards need to be cut at the same angle so that the window will sit on top of the frame securely. We screwed these to the two sides of the mini greenhouse and put one more board across the back to finish off the base.
Then we put 2×4 for uprights in each of the 4 corners to better secure the frame and screwed all of the frames together.
We had a few hinges and a handle leftover from old projects so we attached those to the window top to be able to easily access the mini greenhouse. We then moved the mini greenhouse to the location we wanted it for the winter. Getting a full southern sun is very important, as is access to the house and to the water.
We filled the inside up (but left about a foot of space) with dirt that was in a large dirt pile in our tree belt. We put this right on top of the ground without digging into the ground beneath the mini greenhouse because we only plan on planting things here with shallow root systems.
Finally, we attached a seal to the bottom of the window frame to seal in between the window and the top of the wooden frame. This will help to trap the warm air inside as the days grow colder. We didn’t have anything to seal the window with but thankfully we knew someone that had some extra door “foam”. Perfect!
At this time, we are just using a stick to prop open the window when we need access to water the seeds. We planted 4 different types of seeds that work well in cold weather (Tatsoi, Butter King Lettuce, Chard, and Sugar Snap Bush Peas) and we will see how they do!
The nice thing about this mini greenhouse is that is has a built-in “vent” feature. If the inside is getting too warm, we can simply open the window and let it vent without letting any creatures (or children!) in there by having the door propped open.
We are hoping this mini greenhouse will work well at least into December. With any greenhouse, you still have to remember your limitations for seasonal weather. Since January, February, and March are usually the worst here for cold, we will hope to have this mini greenhouse running until December. Then start it back up sometime in March to capture some early greens if the ground inside is not frozen.
Just 4 days after planting, the greens were already up! Here’s a picture at day 5. By day 7, one week after they were planted, everything has germinated and sprouted. The nights are below freezing but the little greenhouse seems to be doing it’s job! As time goes on, I will post more updated pictures here and on my Instagram page.
Here is the growth after just 2 weeks. We’ve had some very cold temps (last night was a hard freeze again with temps in the teens) but the plants look great! We are now working on building an off-grid solar heater for the colder days and nights. And yes, I realize I need to thin these out! If you’ve ever planted a row of anything with little ones, you understand. 😉
I also wanted to share a picture of our previous mini greenhouse which was a hoop house style. We used this greenhouse into December and through many snows and then started our garden in it in March. Overall it worked extremely well BUT it ended up being destroyed by the South Dakota winds. I would gladly build this style of mini greenhouse again if I had some similar raised beds to what we had previously.
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Do you have any kind of mini greenhouse? What do you grow in it?
Merissa has been blogging about and living the simple life since 2009 and has internationally published 2 books on the topic. You can read about Merissa’s journey from penniless to freedom on the About Page. You can send her a message any time from the Contact Page.
This post on Building a Mini Greenhouse was originally published on Little House Living in October 2018. It has been updated as of August 2023.