Building a cold frame or a hoop house can extend and or provide an early start to gardening. I will look at ways to build both, along with the pros and cons of each.
We may not live on a farm, but we can grow where we live.
It is all about the soil!
DIY Hoop Houses & Cold Frames
by David Proctor
February 24, 2022
Urban Farm Lifestyle Magazine Published Weekly
Cold frames are found in home gardens and in vegetable farming.
They create microclimates that provide several degrees of air and soil temperature insulation, and shelter from the wind.
In cold-winter regions, these characteristics allow plants to be started earlier in the spring, and to survive longer into the fall and winter.
They are most often used for growing seedlings that are later transplanted into open ground, and can also be a permanent home to cold-hardy vegetables grown for autumn and winter harvest.
The typical cold frame is (3) foot wide by (4) foot long, but they come in as many shapes and sizes as one’s imagination.
They can be built as a temporary structure or as a permanent one.
The structures can be built from leftover materials to help reduce cost or they can be purchased from many places online.
The concept behind the cold frame structure is to allow the sunshine to come through a transparent top, which provides light and also will heat up the inside area to help plants to grow.
The structure can be placed over areas where you want to get a jump start on germinating seeds or early planting.
Common produce to plant in cold frames are salad greens and root vegetables.
These structures can be built to where plants or seedlings are moved in and out as the need arises.
One of the problems that should be watched out for is overheating of the plants.
The roof or top of the cold frame is normally attached to the body of the structure with hinges so the top can be propped open to insert or remove plants, and to let out excess heat.
It takes a watchful eye to be sure you do not cook your young seedlings.
It can be surprising how warm the inside can get even during the winter months.
One way to take care of this problem is to use an automatic opener that will open the top of the cold frame when it gets warm and will close as the temperature starts to drop.
You may think that this would be something that would require batteries or an electrical source.
Actually, it is accomplished by the thermodynamics of wax or other materials that will melt and expand as the temperature increases and will contract as the temperature cools.
The material in the cylinder will expand and contract, thereby pushing one rod which will pull another to open and close the top of the cold frame.
Be careful to not let the wind grab the top of the cold frame by attaching a small chain or cord that will prevent damage to the cold frame top and possibly your plants inside.
Univent Automatic Opener
The first method of cold frame construction comes from Vegetable Gardening For Dummies.
By Charlie Nardozzi and The Editors of the National Gardening Association from Vegetable Gardening For Dummies, 2nd Edition
“A cold frame is, essentially, a mini-greenhouse. By growing plants in a cold frame, you can harvest cold-tolerant vegetables year-round, even if you live in zone 5 where winter temperatures can dip as low as –20 degrees F. Cold frames are also great for hardening off seedlings, growing cold-tolerant flowering annuals like pansies, and rooting cuttings from your garden.
Build a cold frame to extend your growing season.
A cold frame usually consists of a wooden box covered with windowpanes or clear plastic. The frame rests directly over the soil in your yard. You can purchase a premade cold frame for $100 to $200, or you can create your own simple cold frame by following these steps:
- Build a 3-foot-x-6-foot box from untreated lumber. Cut the box so that the back is 18 inches high, sloping to a front height of 14 inches.
This sloping angle enables more sun to reach the plants, and it sheds rain and snow as well.
- Hinge an old window sash over the top of the cold frame.
If the window sash has no glass, use fiberglass or polyethylene to create a sealed growing environment You can insulate the cold frame by adding rigid foam insulation around the insides of the cold frame and by weather stripping along the top edge. In extreme cold, cover it with heavy burlap or an old blanket. Remember to uncover the cold frame when the sun comes out so the plants can warm up again.
- Position the cold frame so that it faces south.
If the south side isn’t practical, then use the west, east, or north side in that order of preference. It’s best to put a cold frame next to a structure, such as a house, to protect it from cold winds.
Even though the purpose of a cold frame is to trap heat, on sunny days, even in winter, a cold frame can get so hot that it burns the plants. Check your cold frame once a day on sunny days, opening or venting the top slightly to allow hot air to escape. You can even provide some shade by putting a piece of shade cloth over the glass.”
Key Part No. Size Material
A Side 2 3/4 x 16/28 x 36 inches Ext. Plywood
B Front 1 3/4 x 16 x 36 inches Ext. Plywood
C Back 1 3/4 x 28 x 36 inches Ext. Plywood
D Lid frame 2 3/4 x 4 x 31 inches Ext. Plywood
E Lid frame 2 3/4 x 4 x 38 inches Ext. Plywood
F Cover 1 1/8 x 37 x 38 inches Plexiglass
Tools and Materials
(2) 3 x 3 inch butt hinges (ext.)
(2) 4-inch utility handles
(4) Corner L-brackets (3/4 x 2-1/2 inch)
(1) 3/4 inch x 4 x 8 foot plywood (ext.)
1/8 x 37 x 38 inch plexiglass
Exterior wood glue
2 inch deck screws
No. 8 x 3/4 inch wood screws
Straightedge cutting guide
A similar method to provide a climate for your growing plants is a hoop house.
This is a very easy and cheap way to protect your plants.
The structure is not as rigid as a cold frame but assembling is much easier.
A hoop house also covers the plants but the difference is in construction.
PVC pipes are used since they are cheap and easy to bend.
The pipes are cut to length then bent over the garden area.
They are anchored to the ground or the side of the raised bed.
Raised Bed Hoop House
A center tube is attached between the tubes to provide rigidity.
Then the plastic is placed over the tubes and attached and anchored so the wind will not blow it away.
Access to the garden is normally through one end of the tunnel made by hoops and plastic.
This structure will allow the sun to reach the plants, maintain warmth and keep the snow off of plants.
Bonnie Plants has a good tutorial on building a hoop house and they also provide a material list:
Make a Row Cover Hoop House
Flexible PVC pipe
Spun-bond row cover material or frost blankets
Twist ties or twine
Step 1. Layout your design with the hoops approximately 2 feet apart to avoid sagging. Measure the lengths of PVC pipe you’ll need and cut the pipe using a PVC pipe cutter or hacksaw.
Step 2. Hammer the rebar into the ground at the crossbar points according to your design, leaving approximately 4 to 6 inches sticking out of the ground.
Step 3. Slip the lengths of PVC pipe over the rebar stakes, gently bending the pipe to create arcs or hoops, that are secured on both sides.
Step 4. For added support, run a length of PVC pipe across the top of the hoops and secure it to the tops of the arcs using twist ties or twine.
Step 5. Drape the row cover over the PVC structure. Secure it to the ground using bricks or other heavy material you have on hand.
Step 3. Slip the lengths of PVC pipe
As you can see, both of these structures will help you get a jump start on planting this year.
- The cold frame is sturdy and can be built over a raised bed.
- The top can be automated to raise and lower with the temperature.
- The cold frame takes more skill and materials to assemble.
- The hoop house doesn’t take near the skill and materials to assemble, is rather sturdy but doesn’t have automation for temperature control.
- The hoop house is taller and can be easily built.
- This structure is easy to take down and move.
My money is on the hoop house.
But I really like the cold frame.
You decide what works best for you.
Check It Out!
How to Make a Hoop House for a Raised Bed 4:41
OYR Frugal & Sustainable Organic Gardening
- If building a cold frame, use the cylinder shown above to take the work out of raising and lowering the frame.
- If building a hoop house, keep a thermometer inside to know the temperature.
- Be sure and make the One Call (811) before digging or driving rebar into the ground.
- Have your local supplier of materials make your cuts for you so you just do the assembly.
- Use split rubber tubing and clamps to secure the plastic on the hoop house.
- Add a chain to the raised window of the cold frame so the wind doesn’t blow and damage the window.
Wikipedia. Wikimedia Foundation, n.d. Web. 24 February 2022.
“How to Build a Cold Frame for Your Garden.” – For Dummies. N.p., n.d. Web. 24 February 2022.
“How to Build a Raised Bed Cold Frame.” Bonnie Plants. N.p., n.d. Web. 024 February 2022.
“Make a Row Cover Hoop House.” Bonnie Plants. N.p., n.d. Web. 24 February 2022.
Matheson, Betsy, and Ogden Publications, Inc. “Weekend DIY Project: How to Build a Cold Frame – DIY.” Mother Earth News, 28 Sept. 2011, www.motherearthnews.com/diy/garden-yard/build-a-cold-frame-ze0z11zkon.aspx.