DIY How to build a cheap greenhouse

In this DIY greenhouse tutorial, I'm going teach you how to your own build relatively large (10'x20') greenhouse for about $50. Your prices will vary, but that’s what it cost me to buy everything new. There are many "cheap greenhouses" on the internet, but most are made of PVC, which becomes brittle in the sunlight or are small which, if you are trying to start or maintain a homestead garden, is not likely to meet your needs.  Most require that you already have some of the materials on hand.  (If you already had the materials to build a greenhouse and wanted a greenhouse, I think it's logical to assume that you would have built it instead of looking up cheap greenhouse plans on the web.  But then, I've been wrong before).

So, without further ado…

Materials

6 eight-foot landscape timbers.

200 feet of 550 Para cord.

A spool of twine or string.  You can buy it at the dollar store.

Fence staples as few as you can buy.  You’ll only need a dozen or so

Peel and stick Velcro

10-foot x100-foot roll of clear plastic.  No, it's not “greenhouse plastic”.  I’ve been growing plants under regular plastic for years.  It works just fine. 

10 heavy things you want bury.  These can be anything… rocks, bricks, tree limbs (these will eventually rot), five-gallon buckets filled with dirt.  These can literally be anything, so use whatever you can find.  I once used washing machine parts. It is important to remember that family members are ill-suited for this as they decay rapidly, smell funny, and pollute the water table.

And, drum roll please………. Duct tape.

 

Yeah, we are going to be making a greenhouse out of post and string.  Sound crazy?  Well, it probably is. But the engineering behind it is quite sound, and I assure, you it works.  I learned of this design from illegal marijuana farmers who often hid out in the forests around my childhood home.  (Ah, potheads, they’re like MacGyver …… with nachos).  The beauty of this design is that the shape, size, and materials are by no means set in stone.   But we’ll take more about that later.

 

First, draw a rectangle on the ground 10 feet wide by 20 feet long.  Mark a post hole at the corners of the rectangle and at the center of each of the long sides of rectangle.  Each post should be 10 feet apart forming two squares side by side.

Three post holes on one side should be dug to a depth of 18 inches. Whereas the three post holes on the opposite side will need to be dug to 30 inches.  Once the posts are in the ground, their height should be about 6’6” on one side and 5’6” on the other.  This will give you a slanted roof to shed water.  If you would rather cut three posts off rather than dig those to 30” feel free.  But I would advise against postholes less than 18 inches.  However I know nothing about your soil or your posthole kung fu.  If you wish to use a shallower post, do so at your own risk.

 

Set the post in the ground (duh) as straight as you can and tamp the dirt around it as tightly as possible.

 

Now for the anchors.  Guess what?  You get to dig ten more holes.  Yaay.  For each corner post you are going to need two anchors in line with the edges of the rectangle on the opposing side.  For the two center posts you will need one anchor on the opposite side of the other center post.  (If you have something to use as stakes, feel free to do so.  But make sure they are strong and drive them deep).  Dig your anchor holes at least 18 inches deep about 6 feet away from the post.

 

Tie a length of 550-cord to the anchor of your choice and drop it in the hole, leaving a foot or two of cord above ground. Tie a loop in the above ground end of the cord.   Fill and tamp the crap out of the anchor hole with the original dirt.  Repeat nine mind-numbing times.

 

Now run some 550-cord from your anchor loop across the building over the tops of the post to the anchor loop on the opposite side. Drive the staples into the post enough to keep the cord from sliding off the sides, but not so tightly that you can’t slide the cord back and forth.  Pull the cord as tight as you can, unless you are really big, like me.  Then just pull it as tight as you dare.  Tie the cord to the opposite anchor loop.  Now on three sides of your greenhouse repeat this process, running the cord about half way down the posts using the staples to hold it in place. On the remaining side, whichever side you want your door, run a line of cord from the anchor to the post at a height of about 5 feet, then angling down to the next post.  When finished, each anchor should have two lines running off it.

 

Next, take your builders’ twine and run it in lines about 18 inches apart, tying to the cords and/or the post, leaving an open space to use as a door.  Tie these snugly but not so tight as to deform the cords.

 

Working from the bottom up, start covering your greenhouse with plastic.  Bury the bottom six inches of the plastic in a trench to keep it in place.  Use the duct tape to connect the plastic together.  Also use the tape to attach the plastic to the frame by taping along the cords, overlapping them on to the plastic sheeting.  Be sure to make all your tape connections are inside the greenhouse and thus out of the elements.   Remember, if you feel the need to use more tape, you most likely do.

Finally cut silt vertically in the plastic to use as a door.  Reinforce the edges of the opening with “dum da da daaaaaa” more duct tape.  Use the peel and stick Velcro to close the gap.

 

As I said, the best thing about this design is how flexible it is.  Any material can be substituted for something else that you may have or find cheaper.  For posts, you can use pipe, scrap lumber, trees (standing or fell) an old broken ladder, literally anything straight and fairly strong.  It can be made smaller or larger to suit your needs (and budget).  In the past, I have spanned as much as 21 feet from post to post with cord and you no doubt can too.  But remember, the wider the span, the tighter the cords have to be and thus, the stronger the anchor and post must be.

 

A few considerations.  Most importantly perhaps is drainage and do you have it.  Will the rain and runoff from watering your plants make your greenhouse to sloppy and muddy to use?  If you answered yes, choose another spot.  (Seriously don’t underestimate this one.  I built my first greenhouse in a low spot in my yard.  It rained once and never dried out.  It was miserable to work in and the dead men and elves with luminous eyes were disturbing and mostly unhelpful, but for the one elf who suggested I move my greenhouse 20 feet to higher ground.  I did.  It worked.   Clouds part.  Ray of light.  Angels “Laaaaa”.)

I suggest laying down a layer of mulch to insulate the greenhouse from the “cold, cold ground”. But for me, sadly, it’s not in the budget right now.

If taped properly, your greenhouse will stand up to a surprising amount of wind. I live in hurricane country.  My last greenhouse survived two category ones with only some minor damage before it was killed by a Volkswagen…. Don’t get me started on that.

 

To my knowledge, this is the cheapest way to build a greenhouse, one bigger than a bottle anyway.  I urge you to think long and hard about this design and either built it as is or improve it to suit your needs.

I hope this has helped you in your quest for a budget greenhouse. And I wish you the best of luck using it to grow a homestead garden to feed your family… or to grow weird South American flowers only you care about and take pictures of so you can clog up everyone you’ve ever in your met in your entire life’s Facebook feed.  Whatever you choose, good luck.