Window Greenhouse




About: Building design/consulting in SE Minnesota. Resource based problem solver... in other words, I always take a minute to peek in construction dumpsters :) ---the way some have to workout everyday... i have to...

'The Window Greenhouse' is how I've approached the challenge of getting more sunlight for my starts. A method of creating a greenhouse great for anyone looking for a simple way to extend the season or grow with limited space ---or for renters like us who want a real greenhouse!

Approach. The instructable uses materials around the house. A single plastic bin makes a wonderful greenhouse provided it is clear and has a solid edge that fits in your window... next year i will likely add a second bin to effectively create a 'double-pane' greenhouse... more tips later

Insulation & Infiltration. In this instructable I'll walk through how to effectively create a barrier between your home and the outdoors while installing a window box.

Anyone can do this... I really think this is the easiest way for anyone to get started with a window garden. Perfect for a single family home or urban apartment provided you have a south facing single or double-hung window. ---be careful for people below if you are in an apartment!

----using sketchup? get started with the attached file

Step 1: Test Fit - Complete

Going from the initial test-fit of the plastic bin is a series of steps that involved cutting foam to fit the opening.

Simple Method - the simplest approach would be to cut two rectangles that fit around the bin... there really isn't much to this process. If you are inclined to apply a heavy bead of caulking you can probably get a finished product in only two steps.

Insulated Method - adding a couple extra steps means you'll have a better insulation and air gab. This is a good thing for comfort in the house and for the young seedlings that often prefer a warm environment.

Step 2: Tools & Materials

Most materials are easily found around the house. You may need to buy foam but you can often find scraps around construction sites.


  • Plastic Bins - commonly referred to by their brand names... Sterilite or Rubbermaid. Any bin will work provided it has a solid edge and fits your window. I find a deep bind around two feet is ideal. Even better if you can use two... it effectively creates an extra air layer much like a double pane window. ----you may find them better priced in the walmart plastic bin aisle
  • Rigid Insulation - a building product that shows up on most building sites here in MN. A really wonderful product for crafts. The material comes in a standard 2" depth. Any of the colors (yellow, pink, blue) work fine for this project. Always available new at a big box.
  • Duct Tape - happy to share a use for this product that actually fits its name! Duct tape is sold to seal air gaps and that's exactly what it can do for you on this project. If you're on this site you likely own a roll (or several)... you can always get lost searching here on amazon.
  • Sealant - not show in the instructable... like many of my garden projects they are planned as tests and will be modified each year. I see it as worth adding a bead of sealant to cut down on air infiltration between the foam and plastic bin. ---here's a link to a waterproof sealant I found on amazon. I think they are selling small tubes now at dollartree.


  • Olfa Cutting Tool - yes, this really is my favorite. It's something I use on most craft/building projects. Here it is particularly useful to extend the blade. The Japanese steel really holds up to the rigid insulation that has tough fibers... it will quickly wear down a kitchen knife. ---impressed. the Olfa L1 price actually came down to $6.95. It's always hovered around $10.
  • Cutting Mat - always hand and a good way to protect your worksurface. I'm simply using a 1'x1' mat so that if my blade runs past my material I land on a solid surface. ---there are a lot of options.
  • Sharpie - easiest way to write on foam. also useful to make a notch with you blade.
  • no ruler method - you may find it strange but it's pretty straight forward to work this project without a ruler... I find it convenient to mark on the foam. A couple scrap pieces of foam are also useful to transfer dimensions.

Drawing File - Please see the drawing file is available for download. You may find it useful to scale the window or look at the layout in a 3D drafting program.

Step 3: Header & Sill

---note that in this diagram UP is to the LEFT.

Width -at this point you're looking for the width of the window plus 2". This should give you a workable width and 1" extra at each end.

Depth - the foam I recommend comes as a standard 2".

Height - more detail below on how to create the header and sill.

Header & Sill

See the images for how I notch the header and the sill. The idea here was to be roughly centered in the foam but to allow for a thicker layer on the inside of the window. There are two reasons to keep the inside edge thicker...

  1. Insulation - A thicker surface allows for more insulation and greater contact along the edge of the plastic bin.
  2. Support - The weight of the bin should sit on the window sill and pull against the header... that said, a thicker lip of insulation will also catch a portion of the load and it's useful to have a little over 1" of material.

Sill Channel - wherever possible a channel is better than an angle. The channel makes for a tight fit that really cuts down on air infiltration. In the next step I'll show how to cut the channel.

Step 4: Cutting Technique - Sill Channel

Cutting foam is very simple. The main caution is to not feel too confident. The knife can move quickly and that's how most people cut themselves. Make deliberate cuts.

  • Score - you want to run a first pass along the surface. Easy to use a straightedge or use a finger along the edge to guide your blade. For this step you may want to keep your blade short
  • Deepen the Cut - once you have an initial path for the blade make another couple passes to get the desired depth. For this sort of 'rabbet' cut (to borrow from carpentry) you want to first cut at 90 degrees.
  • V-Cut - after cutting straight down on the edge you'll come at an angle to cut material. I often work with an extended blade but this isn't necessary.
  • Loosen Material - from there you can use the edge of the knife or even a screwdriver to remove the loose material.
  • Compaction - when insulation is packed down it loses it's insulating ability. That said, it works well in our case because it helps create a tight seal. The main challenge in our case is air infiltration around the perimeter.

Step 5: Cut the Width

See that in the diagram there are three sections that add up to the width of the window. The exact width of any single piece doesn't matter as much as them all adding up to the width.

  • A - Left Foam
  • B - Plastic Bin
  • C - Right Foam

My preference is to have the bin located closer to one side or the other. I suggest starting with the long side... if you have problems cutting the edge to match the bin you can always make it the short side.

Extra Length - remember to allow an extra 1" on each side. This will give you a lip the same way you have a lip against the window in Step 3.

Step 6: Scribed Edge - Fit to Bin

Yes, it's helpful to keep your side pieces long. The process of fitting, or scribing, the edge is straight forward but if it's your first time you may want a test cut. (some tools, like this veritas log scribe, are way too intense)

Scribing - there are a number of carpentry tools to help scribe. It is a common practice when fitting trim along edges or flooring that isn't straight. I find for our case a sharpie is the best tool.

Notching - to complete this cut you'll need to cut in two dimensions. The easiest way is to first take off 1/2" of material and then take off more... you'll likely want to take off a total of 1". Some bins aren't exactly straight on their top lip. You can add an angle if you want bring out your inner sculptor. The easier option is to simply use a piece of duct tape along the joint.

Step 7: Finished Notch

Useful to fit the cut piece in place against the plastic bin and making slight adjustments for your cuts. Think of this part of the cutting more like carving.

This bin has a straight edge and then a curved lip. The notch allows the bin to rest up against the foam very similar to how the header rested in Step 3.

Step 8: Enjoy!!

Thank you for following!

Yes, this project should help start your plant babies and get the garden off to a good start. Here in MN we have a winter that doesn't seem to end. Our last snow fall was only a few days ago.

Hope you find this useful and are a step closer to starting a window garden.

Thanks, Jeff

For more gardening instructables see a few I created from last season:

Oh, and consider voting below in the Gardening Contest if you've enjoyed this post!!

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    13 Discussions


    5 weeks ago

    Be careful with insulation foam, it’s loaded with things like flame retardants and mold inhibitors.


    5 weeks ago

    instead of using rigid insulation foam to fill the gap, just use some old memory foam from a pillow or mattress. Squeeze it a bit and put it in place, it will expand out to seal the opening.

    4 replies

    Reply 5 weeks ago

    I would recommend against using memory foam, as it's porous enough to allow air to pass through, and it isn't waterproof. The harder styrofoam type of insulation used in this particular instance has a vapor barrier on the outside of it, in addition to it being much more impermeable than memory foam (in some cases, it's impermeable to water and air entirely, which is why you see it used in basements and crawl spaces for insulation against foundations).


    Reply 5 weeks ago

    All of that may be true but, anyone putting a plastic tub into their window to grow plant starts isn't looking for a long term solution. The tub is only going to be there for a few weeks. The amount of moisture that will come through memory foam is negligible compared to the amount of water coming in around the edges of rigid foam that isn't cut perfectly to fit the open spaces. People generally have trouble measuring and cutting things like this. Memory foam can be oversize and will expand into those nooks and crannies. One could also cut the memory foam, then put it in a small plastic bag, then put that into the opening.


    Reply 5 weeks ago

    You're severely underestimating how porous memory foam is: it's used as a pre-filter for air intake ducts on combustion engines, vacuums, dust collectors, and other filter-based applications. It's not water proof, and water can soak through it in a matter of minutes. It's not something I would recommend even using in a temporary setting such as this one, because if you're bothering to use insulation at all, then clearly you're trying to reduce the amount of thermal energy lost or gained between the outside environment and the inside one. That alone is an indicator that something like this isn't quite as "temporary" as you suggest.

    And, for what it's worth, styrofoam insulation isn't that difficult to cut. An Exacto knife and a Dremel or some rotary tool are really all you need.


    Reply 5 weeks ago

    Know that with the rigid foam I have had no water coming into the house. Even with a driving rain. That is part of the reason for the 'z barrier'. Closed foam is far superior to open cell foam... I believe the memory foam pillows are an even lesser quality than commercial open cell. Thank you both for the discussion!


    6 weeks ago

    What a useful project!! And not just that, it's super cheap too :D

    1 reply

    Reply 6 weeks ago

    Javier! Appreciate your noticing the thrift! Certainly ways to add cost and make a cleaner finished look but anyone can get this setup going.


    6 weeks ago

    This is SUCH a good idea! We also just got snow a couple days ago. I definitely need the extra help getting seeds started :)

    1 reply

    Reply 6 weeks ago

    Thank you! Definitely give it a shot with a double bin. When that snow hit I was wishing I had the 'double pane' bonus of an air gap. ---as always big fan of your work!