Step-by-Step Inexpensive Patio Greenhouse or Super Simple Cold Frame

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Many of us are considering new ways to increase yields from our gardens this year. Potential supply interruptions and increased costs at the checkout are compelling us to think outside the box and find a way to compensate for the world changing around us.

Do you need a greenhouse that is inexpensive and simple to construct? A poly sheeting covered a-frame is the answer to your needs. It can be constructed over a small raised bed on an apartment balcony or over a larger bed in your backyard. The more materials you repurpose the less expensive this little greenhouse will be. Mine was FREE!

In this post, I’ll share exactly how to build an A-frame greenhouse over your garden bed in just a few easy steps.

Dream of a Greenhouse No More

Have you been dreaming of a greenhouse packed to the rafters with veggies bursting forth from its interior? I sure have, and it has inspired me to get creative. I would like to share with you the solution that I have come up with that is free, or nearly free, depending on your resources at hand.

You can create a “Poly Sheeting Covered A-Frame Garden Bed” if you live in an apartment with a small patio, or on a 300 acre homestead. This greenhouse, cold frame, or a mini version of a greenhouse can be created for next to no cost. Finally, a greenhouse that anyone can afford.

The Inexpensive Solution to Extend Your Growing Season

I felt challenged recently to create a solution to my limited growing season. I have been frustrated by the recent bouts of frost and freezing temperatures. Tender seedlings across the country have fallen victim to the sting of Jack Frost, right at a time when we are depending on our gardens to be productive.

I have a great solution! I built an A-frame with a plastic sheeting cover. The materials I used are all scraps that I had lying around the homestead, so the end cost was free. You may not have all of the materials but, they are inexpensive and, with some creative thinking, can be sourced for free.

Materials you will need

I started with a wood crate that the previous owner of our property left behind. It was a crate from a bottle shop that wine had been shipped in. You could easily build one out of scrap lumber or an old pallet.

Planter Box

You may also have a preexisting planter box or raised bed that could be used. Or, check with your local businesses and see if they ever have wood crates that are available.

Plastic Sheeting

You will need some form of clear or opaque plastic sheeting. You may find it under the names of plastic sheeting, polyethylene plastic sheeting, or under the brand name of Visqueen. I used a recycled piece of poly sheeting. You could use a plastic wrap of any kind that is large enough to cover your box. If you need to purchase your poly sheeting it can be found at your local hardware store in the painting section.

You will want to get a thick, heavy mil plastic. Mine is 8 mil, the higher the number the heavier the plastic. You want it to be heavier so it will hold up to the elements.

Miscellaneous Tools and Hardware

You will also need a few tools (including power drill and saw), some scrap lumber, some nails or screws, and a couple of clothespins or clips.

Basic Assembly of the A-Frame Poly Sheeting Covered Garden Bed

This is a very simple project that only takes about an hour or so to put together. You don’t need to have a background in construction to do this. This is something anyone can try.

Garden Box Assembly

If you are working with a preexisting bed, you won’t need to construct the planting box. If not, you will need to assemble one. Any size will work as long as you remember a few things.

Raised Garden Box Width

Don’t make it too wide. If your box is too wide you will not be able to access the center of the bed. The bed should be a maximum of 4 feet wide if you can access it from both sides. If you can only access it from one side, it should be about 2 ½ feet wide.

Raised Garden Box Length

Your garden box can be as long as you want but remember that you will need to stay within the confines of your upper support. I would suggest no longer than 8 feet.

Raised Garden Box Depth

It needs to be deep enough to accommodate the variety of plants you select. If you are planting lettuce and herbs 5 to 6 inches deep is sufficient. Tomatoes, carrots, and deeper rooted plants will require a soil depth of at least 18 inches.

Drainage

Many garden boxes are built right on the soil so drainage isn’t a concern. Make sure that you allow for drainage if your container has a bottom.

Attach A-Frame Upright Supports

Once you have your box you will need to attach your uprights. You will want something that is strong enough to support a small load. I would recommend a 2×2 or 2×4. These will need to be long enough to raise the plastic up off the tops of the plants.

I decided that I would make my uprights about 3 feet long. This provides 2 feet of growing space between the plastic and the soil. The wider your bed, the taller this support will need to be. I fastened these boards to the ends of my crate by screwing them in from the outside. If I need to remove them later in the season, I can simply remove a couple of screws and slide the board out.

Attach Top Support

Run a board the same length as the box between the two uprights. Again a 2×2 or 2×4 is a good option here. Then screw the support board into the tops of the two uprights.

I used some lath strips to make the “A” portion of the A-frame. I choose lath strips because they are thin and I can easily use clothespins to button the plastic in place. They don’t provide any structural support so there is no need to use heavy-duty boards.

Lath is very easy to cut using a little hand saw. You will want to pre-drill all of your holes on the lath because it splits very easily. Cut to length and screw into place at the top of your A, and at the corners of your box.

Attach Poly Sheeting to the A-Frame

Once this frame is constructed you are ready to apply the poly sheeting. This will be cut into 3 different pieces, the top and two end flaps.

  • Starting with the top portion, simply drape a piece over the frame, cut so the plastic hangs about 3 inches below the top of the planting box.
  • Next, fasten it to the top board by either stapling it in place or by screwing a lath strip along the support and sandwiching the plastic between them.
  • Attach a board on each side at the bottom of the plastic, even with the top of the planting box.  I cut the plastic about 2-3 inches past the top of the box so it overhangs the box enough for the board to be attached to the plastic with staples, you can then either screw this into the sides of your box or fashion a cleat. I opted to screw it in. When I want to open the bed up, I just back out the screws and roll the plastic up.
  • When applying the plastic, be sure to pull it tight so it doesn’t sag. This will help it hold up in the wind, snow, and rain, and aid in shedding precipitation.
  • Apply your end pieces of poly sheeting. You will need to sandwich a piece of plastic between the ends of the bed and a lath strip. Drill and screw in place.
  • Then bring it up and poke a few holes in both the flap and the top piece of poly sheeting along your A-frame lath strips. This will be where you place your clothespins to hold up your end flaps. You need to be able to open the plastic up during the day because if you don’t ventilate the bed, your plants will likely die from overheating.
  • Pin in place and trim the excess plastic off. Leave a 2-3 inch flap.

Planting Your Poly Sheeting Covered A-Frame Garden Bed

Now the fun part! Fill the bed with soil.

Soil Mixture for Garden Bed

You can use a bag mix if your beds are small and you only need a little soil, or you can create your own raised bed/potting mix. This is how I make my mix.

  • 1 part topsoil/ black dirt
  • 1 part peat moss
  • ½ part compost or composted manure. (It is important that you use a fully composted product or you will burn your roots and kill your plants)

This soil mixture is just a suggestion. You can use whatever is available to you or whatever you prefer. Just make sure that you provide enough nutrients for your plants to grow. Those nutrients are held in the compost portion of your mix. The other two ingredients for all intents and purposes are void of nutrients, or at the very least lacking. Properly amended soil is the key to a productive garden.

Select the Right Plants for Your Garden Bed

When selecting plants for a raised bed, it is important to take into consideration the size and depth of the bed as well as the amount of sunlight it will receive. These factors will dictate what will work in your growing space.

When I made this mini version, I did so mainly to demonstrate the process so I didn’t have a planting plan. I decided that this would be a perfect size to plant a bush cherry tomato and some kitchen herbs. The dimensions are 3 feet x 2 feet x 18 inches high and it receives full sun.

Why You Should Consider Building an A-Frame Greenhouse

My main reason for building covers for my raised beds was to extend my growing season. I live in zone 3a, and our season is short and unpredictable. This option will allow me to plant earlier, provide protection from unseasonal cold snaps, and allow me to harden my plants off in bed, as opposed to having to take my potted plants in and out daily.

After planting, I roll up the poly sheeting cover each day for an increasing length of time until the plants are acclimated to the direct sunlight. Remember to roll the sheeting back down before frost comes.

Once the threat of cold weather has passed, the poly sheeting can be removed and the frame can be used to support bug net or even shade cloth depending on your needs. You can also use the frame to attach rope for trellising vining plants or as a support for plants such as tomatoes and peppers.

This A-frame also gives you the option to cover your plants and provide protection when a severe storm is coming, affording you the ability to quickly provide protection from driving rains, intense winds, and hail. There are a ton of uses for this project.

I was initially planning on building PVC or cattle panel supports for my Poly Sheeting covers. I decided that before I went and invested a sizable amount of money into materials, I was going to try doing this for free. To my surprise I really liked its functionality and versatility.

I am in the process of putting in 750+ sq ft of raised bed growing space. I will be installing these on all of my beds. The cost is minimal and the A-frames create a lot of additional growing options.

Poly Sheeting Covered A-Frame Garden Bed

I feel the need to become more self-sufficient and able to produce more of our food. All of us have started to see shortages or price increases, and it raises concerns. I wanted to write this to encourage you to try growing something, even if you have never tried.

Even those with limited space could have something like this on an apartment balcony or urban patio. And if your finances are holding you back, try using what you have to fabricate a solution. Something as simple as an old wooden bookshelf laid on its back and filled with dirt would work. You don’t have to have 20 acres and endless financial resources to be able to create the same thing as a large professional greenhouse is going to provide.

Don’t get me wrong, I would love to have a big beautiful greenhouse, but it’s just not practical at this time. So don’t let these limitations hold you back from growing your own food. I hope this gives you a little encouragement to try something new and start growing. Even just one small bed can grow quite a bit, so give it a try!

Thanks for being part of the solution!

Jonathan and Kylene Jones

Beth Lestico

Beth is an avid outdoorswoman who spends most of her time hunting, fishing and homesteading with her husband and 2 children. She is passionate about self-sufficient living, gardening, food preservation, learning about wild edibles and traditional skills. Being a high energy and curious person keeps her motivated to constantly learn new skills and methods of doing things. She loves hearing from others about new ways of doing things as well as sharing her experiences with anyone who is interested.