Build an Easy DIY Cold Frame Greenhouse + Free Plans

Here's how to salvage and repurpose old windows made from perspex to build a DIY cold frame greenhouse to protect your plants in harsh weather.

This easy cold frame uses basic tools, skills, free plans, step-by-step instructions, and video to follow along to help you save money!

Do you love gardening and growing your own food? Do you want to extend your growing season to enjoy fresh salads and herbs even in the colder months? Then the good news is that this tutorial is for you!

Here's how to make a small cold frame with a lid using recycled materials like old clear plastic or perspex which I found in a bin. Interesting fact: in their former life, they were narrowboat windows!

Being on a budget myself, you'll find this project is easy, cheap, and eco-friendly. And it only requires basic tools, materials, and skills. And if you don't have loads of perspex, make the side panels out of wood!

Let's get your plant growth started!🌱

Jump to:

• 🌱 What is a Cold Frame?
• ✔️ Why You'll Love This Project
• ⚒️Tools and Materials List
• 📏Free Cold Frame Plans
• 📋 Step by Step Instructions
• 🔨Material Substitutions
• ⚖️ Project Variations
• 🧽 Care and Maintenance
• 💡Pro Build Tips
• ❓ FAQ
• 💰Project Cost
• ➕ More Plant Projects
• 💬 Comments

🌱 What is a Cold Frame?

If you're new to cold frames, they are like a miniature greenhouse. They're usually a basic box frame or structure with a clear lid to allow sunlight and heat retention to create its own microclimate when it's colder outside.

They are designed to help protect plants and seedlings from cold weather like frost and snow, to help you get more growing time during the year.

They can be basic or luxurious as you wish. You can use cheap plastic bottles to over plants, all the way to more expensive greenhouses. They are perfect for small gardens, balconies, or even a narrowboat roof.

✔️ Why You'll Love This Project

Here are just a handful of reasons why we think you'll love making this cold frame gardening project!

• You can open the top on sunny days
• You can swap perspex for many different materials
• Less materials are needed as it has an open bottom
• It should take about 2 hours to build with hand tools
• It's much cheaper to make than buy a new cold frame
• It's a great way to recycle old materials and household items
• Perfect for growing tender plants from Autumn to early Spring
• Creates shelter and trap its heat source if you have any cold wind in early Winter
• It's a simple DIY, simple design and a simple wooden frame that anyone can make
• You can grab my free plans below and put your money towards building a basic toolset

⚒️Tools and Materials List

Please note that as an Amazon Associate, I earn from qualifying purchases made through affiliate links.

Old 5mm perspex - or use any clear plastic materiar or wooden sheets with plastic for a transparent roof. See "Substitutions" for more household items you can use

Hand saw - this is for gentle and safe cutting which I find more accurate than a vibrating jigsaw which can bounce with plastic. You can use a table saw or compact circular saw with a guide or straight edge for quickness, but it's not vital

Masking tape - this is so you can easily see your pencil cut marks and easily peel off when you're done. Or feel free to use a permanent marker

Scraper - this is only needed if you're using old plastic boat windows like me and need to strip off the old sealant or stickers, etc

Tape measure - to measure twice, cut once!

Combi drill - for drilling pilot holes in the plastic sheet and wood. Note, I recommend drilling holes in the plastic slightly bigger than your screws so that it will be easier to screw through the plastic to the wooden cold frame

Drill bit - instead of using a drill bit slightly smaller than the screws I used, I used a 5mm one, but only drilled shallow pilot holes through the wood. (Too deep and the screws won't have sufficient grip in the wood)

Screws - I recommend stainless steel screws slightly shorter than the wooden frame you're using. Note, as they are not cheap, I cheated and used wood screws and sprayed them with grease to prevent them from rusting

Stainless steel washers - don't skip the washers! I used stainless steel so they won't rust and they're also really cheap. They take pressure off the plastic while screwing it together and add strength to frame

Workbench or DIY sawhorses - just use whatever you have, but nothing you treasure, like a kitchen worktop! In the photos, you can see I used stacked boxes!

38mm x 38mm (1.5" x 1.5") timber - or similar thickness for screw depth (AKA studs) for the wood frame which also work as legs/feet. And some offcuts for the lid as stopblocks to prevent it from slipping off. You should be able to buy this from most lumber yard or DIY stores.

Note: you don't need legs if you want to place your cold frame on the soil and fill it with straw bales. My legs slightly protrude at the bottom for a vent and rain to freely run under as mine sits on our narrowboat.

📏Free Cold Frame Plans

To print my free plans for a cold frame, feel free to right click and save the image first.

Please note that if you want a different design like a bigger cold frame plan using all perspex, then I recommend adding some horizontal wooden frame lengths to make the plastic more rigid.

You could screw your box frame together first with a pocket hole jig for ease, then mount the perspex faces on.

📋 Step by Step Instructions

You can refer to my shorter printable guide in the how-to card at the bottom of this post. However, I recommend reading the entire post as I have more detailed tips, tricks, and step-by-step images.

Tip: if you're placing cold frame on a patio or flat but uneven textured surface, a great idea is have the frame protrude at the bottom to act as feet and prevent wobbling. Also, it creates a vent and prevent rain from pooling.

🔨Material Substitutions

Here are some simple swaps you can make to your own cold frame and still offer better growing conditions for your less cold-tolerant plants:

Perspex

Old shower curtain - if you use more wood for the internal framework so that your box doesn't rely on the perspex to hold its shape, you can staple an old clear shower curtain to the framework and make an additional frame for the lid. You could also use hinges!

Shower doors - a single glass shower door usually pivots on a hinge and is transparent to let light in. They can be picked up cheap on eBay and are a good idea to build a frame for it with an angled slope for rain to slip off

Old glass doors or old window pane - although much heavier for the top of the cold frame, you can put them to good use if you want to build a large cold frame for the garden. Another bonus is that they already have chiseled notches for hinges.

Clear corrugated PVC - a great solution for cold frame plastic sheeting that is usually used as clear roof panels. These are easy to screw with washers

Polycarbonate roofing sheets - although not cheap brand new, have a look for used sheets on 2nd hand selling sites, or for people dismantling their old conservatory roof, etc

Old picture frames - repurpose old picture frames with a sheet of glass for the cold frame lid. Although you will need to add some frame pieces behind, all the way around the edges and edges of the backs.

Use majority wood - you don't need to use as much clear plastic as I did, Instead you can use my free cut list and cut them out of wooden sheet material like OSB, treat plywood or attach tongue and groove, lap panels to a frame

⚖️ Project Variations

Here are some different and best ways we think you can personalise this simple cold frame design for your own gardening needs:

• Add a hinged top - by building a simple box frame for the lid along with wood mounted on the inside of the back panel at the top, you can make a hinged lid. You can add a prop-up baton to keep it open so that your plants survive in a warm climate
  
• Cover with plastic bottles - build a wooden stud frame and screw slimmer strips of wood around it with plastic drinking bottles slotted through to reduce waste. I think this makes the perfect local community project while recycling waste
  
• Front doors - Depending on your chosen plant, you could make it front facing with doors instead of a solid front piece with shelves, and even an Apex roof.
  
• Raised bed - you could build raised sleeper garden beds with old railway sleepers to work around a clear top, or make a hoop house with PVC pipes and add a plastic cover like a mini polytunnel. This may not be suitable if you have any strong winds
  
• Folding cold frame -if using sheet wood material for the side panels that are thick enough to mount screws, you can make it a folding by adding hinges. Then fold and store it away with the lid in a shed, etc

To allow your plants to breathe in hot weather, you could store them on this large DIY plant ladder.

🧽 Care and Maintenance

• If not using pressure treated timber, then you will need to use a preservative on the wooden framework to protect from the elements
  
• Use stainless steel screws and washers where possible. If not, then you can grease them to help prevent rusting

❓ FAQ

💰Project Cost

As I used recycled materials and offcut wood, I didn't have to go out and buy anything new for my vegetable garden. But the only real spend here was using washers and screws I already had.

Total cost = £1 / $1 (existing screws and washers)

Have Your Say

I'd be interested to hear what you would do differently for your Winter garden. What you do find is the best option on a budget? The best places in your garden?

And how do you tackle gardening in cold temperatures in your country? Drop a comment below - I'd love to hear!

➕ More Plant Projects

Looking for more DIY gardening projects like this? Then you might like these for when the cold season is nearing the end:

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