How To Build A DIY Mini Greenhouse: Extend Your Growing Season

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Imagine harvesting fresh veggies from your garden even as snowflakes are falling! A DIY mini greenhouse for your garden bed might be your secret weapon for year-round growing.

Some people, including my wife, do not know when to call it quits in the garden. Ash wanted to conquer (or combat) the elements to squeeze more produce out of our garden. Hence the DIY Mini Greenhouse.

We live in the Midwest, near St. Louis, MO, which is in growing zone 6b. We have a pretty good growing season, but once we hit October it’s pretty hard to grow anything outside until about April. If you live in a warm climate, then you may be able to enjoy a longer growing season.

With Missouri weather, we can also have all four seasons in a 24-hour period. Especially in winter when we can have 6 inches of snow one day and temps in the 70s the next.

I was hesitant a few years ago when she first asked if we could build a greenhouse for one of our garden beds. I researched to see what types of options were out there (most were very pricey), so this year I looked around to see what materials we had laying around or could use to make a DIY mini greenhouse on the cheap.

What is a Green House?

According to Britannica a greenhouse is a building with glass or plastic walls and roof that protects plants from extreme weather conditions (source). Some are more involved and extravagant than others, but a DIY mini greenhouse can get you where you want to go.

A greenhouse is a little different than a cold frame, which is more often used for a smaller space and a few cold-weather plants or lettuces. Sometimes the two overlap in their designs and you get a hybrid. Both offer the some of the same benefits: keeping plants from freezing in cold temperatures.

A true greenhouse would be able to sustain warm weather plants all year round, but we aren’t a professional farm. We are just wanting to keep the frost and icy wind away, and a winter frame or DIY greenhouse can keep the soil and air close to 10-20 degrees warmer than outside.

Why Build a DIY Mini Greenhouse?

There are two reasons we built our mini greenhouse: first, for experiment’s sake (we’ve tried other versions in the past and we are just trying to improve), and second, because we love to have some fresh greens in the winter! We have tried a miniature hoop house in the past, but we didn’t have the plastic secured and the wind would often blow it off, or it would cave in.

This year, we are aiming to see if we can grow some kitchen staple items like beets, cilantro, kale, spinach, and lettuce this cold season. I also plan to start some seeds early along with my normal winter sowing in milk jugs to see which works best.

Green House Options in the Suburbs

Generally, you have a few options:

• Large Greenhouses or Hoop Houses
  • Arched design with translucent plastic sheeting
  • Straight-forward to construct
  • Usually big, expensive, and meant for large-scale growing
• Small Greenhouses
  • Often prebuilt or made from a shed
  • Can be DIY’d with doors, window, or plastic
• Cold frames
  • Often made of upcycled windows
  • Usually made with a slanted lid
• Portable Cloche-Style Cold Frame

We live in the suburbs and have an HOA in our neighborhood, so we can’t put sheds, storage containers, or permanent structures on our property. We needed to make something that could be easily removed or dismantled after winter.

If you have the space, time, and funds you can definitely go for a prebuilt greenhouse. I know Ashleigh would love this greenhouse from Costco. But being just a hint of a homestead, we set to work on our own miniature suburban version to test out this winter.

We decided to combine all of the options based on what supplies we had around the house into our own budget-friendly winter garden bed. The beauty of DIY is that you can customize your greenhouse to fit your unique garden needs and style.

Tools and Materials for DIY Mini Greenhouse

• Tools
  • Measuring Tape
  • Screwdriver/Drill
  • Saw(s) for cutting boards and PVC pipe
  • Staple Gun
• Materials
  • 2 x 4 boards for the frame
  • PVC pipes – 1/2″ x 10′ schedule 40
  • Metal Pipe Straps 3/4 in. Standard Fitting
  • Box of 3″ – 4″ screws for connecting the wood frame
  • Box of 1.25″ screws for pipe straps, hinges, and tacking strips
  • 2-4 Hinges (depending on bed size)
  • Greenhouse Plastic
  • 1 x 1 boards for tacking down plastic
  • 2 Handles
  • Zip Ties
  • Staples
  • Lock or Latch (optional)
  • Duct tape for any rips in plastic

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Planning the Size and Location

We went ahead and made our greenhouse the same size as one of our current garden beds, so we didn’t have to build two things. The garden bed gets full sun, has good drainage, and is easy to access even if it is snowing. You also want to be aware of your access options. This frame is hinged, so there has to be clearance to prop it open. Different access options can be used to fit your situation- hinging may not suit your space.

Our DIY mini greenhouse ended up being roughly 4 x 8. I would have been more precise with my measurements had I known I’d eventually be writing a blog post about putting together a greenhouse! 4 ft x 8 ft sounds a lot better than 50 in x 100 in.

Instructions and Tips for Building a DIY Mini Greenhouse

Preparing and Constructing the Base

• Measure and cut the materials – “Measure twice, cut once,” is a saying my grandpa frequently said. It’s important to have the same dimensions as your garden bed in order to have a solid resting foundation and a relatively seamless fit when the greenhouse cover is in position.
• Pilot Holes – A pilot hole is made using a drill bit slightly smaller in diameter than the screws you intend to use. It’s always good to make pilot holes before screwing the boards together to prevent boards from splitting.
• Building the Frame – You have options to connecting the boards together, I chose to use screws of sufficient length (3″ – 4″ decking screws) to hold the frame together from an assortment of screws based on my “stock.” You could also use nails if that’s what you have around already.
• *Lesson learned* – It would be to your advantage to put a 1×1 board across the base of the frame before mounting the PVC pipes/conduit straps. This will prevent the pipes from slipping down when not on a flat surface…ask me how I know…We had to do some finagling once we got the frame on the bed – the pipes slid down the holders, so we had to add a screw below each end of the PVC to hold up the arches.

Forming the Frame with PVC Pipes

• You will want to decide how high you want your hoop house to be and buy the length of pipe accordingly or just buy 10 ft length PVC pipe like I did and utilize the height it gives you.
• The length of your garden bed will determine the number of pipes needed. It’s probably good to have a hoop every 18″-24″ depending on the amount of snow you could get during the winter and based on the wind exposure of the garden bed location.
• Allow for enough pipe to “strap” perpendicular to the top and sides to allow for added strength.
• The number of pipe straps will depend on the number of PVC pipes you opt for. You’ll need two per pole.

Put the Frame Together

• Space the pipe straps evenly across the length of the frame every 18″ – 24″ depending on your frame size and expected winter elements.
• Simply slip the PVC pipes in the strap on one side, then bend and place the opposite end in the strap on the other side of the frame; repeat until all of your poles are in. Be careful when bending the pipes as they will be under tension and will want to spring up.
• Up until now all of the “hoops” are made with the PVC pipes, but they will be wobbly. It will be a good idea to connect them to add strength and rigidity. I chose to take the simple path and cut a few PVC pipes to the length of my frame, drill holes on each end and then zip tie them together.
• You can get fancy and use pipe fittings to connect the hoops to the horizontal braces, but that will involve a lot more measuring and cutting.

Adding the Greenhouse Plastic

• Remember, “measure twice, cut once.” I had to use a strip of duct tape to close the plastic back up because I didn’t listen to my grandpa’s advice!
• Unfold the plastic sheeting, drape it over the hoop frame, and line up the sheeting on one side first then tack down and fold the sides. We opted to fold the corners like you’re wrapping a present.
• We used a combination of staples and sections of 1x1s to tack down the plastic. The staples were used first to get the plastic in place and then the 1x1s were screwed in strategically to secure the plastic against the inevitable winter elements. Wind is strong!

Installing Hinges and Handles on the Greenhouse Base

• After you have an assembled hoop house frame, you’ll want to be able to open it to access your gardening area and to crack it open if it gets too warm out.
• I went to my “stock” of hardware that I collected over the years and found some random handles and hinges. You will just want to make sure they’re of sufficient quality and sizing to stand up to the weather and weight of the frame.

Securing the Greenhouse to the Garden Bed

• Attach the hoop house frame by securing the hinges to the garden bed.
• It will also be a good idea to put a safety chain, rope, etc. to prevent the hinged hoop frame from opening too far if it catches a gust of wind, excessive strength when opening, etc. (we just used some string we had).
• Keep a stick handy to hold the frame in the “up” position while you’re tending to the garden.
• You will also want a system to keep the frame “closed” to keep the wind from blowing it open. A variety of methods can be employed such as tying the handle to a spot of the garden bed frame, using weight in some capacity, or using some sort of latching hardware. We opted for the latter and used a latch from my “stock”.

Final Touches to the Greenhouse

• Examine how the frame sits on the garden bed and make sure there aren’t too big of gaps between the two surfaces. If a large gap does appear, try applying some foam weather stripping.

Plant Away and Keep that Winter Weather at Bay!

Preparing and Constructing the Base

Measure and cut the materials – “Measure twice, cut once,” is a saying my grandpa frequently said. It’s important to have the same dimensions as your garden bed in order to have a solid resting foundation and a relatively seamless fit when the greenhouse cover is in position.

Pilot Holes – A pilot hole is made using a drill bit slightly smaller in diameter than the screws you intend to use. It’s always good to make pilot holes before screwing the boards together to prevent boards from splitting.

Building the Frame – You have options to connecting the boards together, I chose to use screws of sufficient length (3″ – 4″ decking screws) to hold the frame together from an assortment of screws based on my “stock.” You could also use nails if that’s what you have around already.

*Lesson learned* – It would be to your advantage to put a 1×1 board across the base of the frame before mounting the PVC pipes/conduit straps. This will prevent the pipes from slipping down when not on a flat surface…ask me how I know (see above picture)…We had to do some finagling once we got the frame on the bed – the pipes slid down the holders, so we had to add a screw below each end of the PVC to hold up the arches.

Forming the Frame with PVC Pipes

You will want to decide how high you want your hoop house to be and buy the length of pipe accordingly or just buy 10 ft length PVC pipe like I did and utilize the height it gives you.

The length of your garden bed will determine the number of pipes needed. It’s probably good to have a hoop every 18″-24″ depending on the amount of snow you could get during the winter and based on the wind exposure of the garden bed location.

Allow for enough pipe to “strap” perpendicular to the top and sides to allow for added strength. The number of pipe straps will depend on the number of PVC pipes you opt for. You’ll need two per pole.

Put the Frame Together

Space the pipe straps evenly across the length of the frame every 18″ – 24″ depending on your frame size and expected winter elements.

Simply slip the PVC pipes in the strap on one side, then bend and place the opposite end in the strap on the other side of the frame; repeat until all of your poles are in. Be careful when bending the pipes as they will be under tension and will want to spring up.

Up until now all of the “hoops” are made with the PVC pipes, but they will be wobbly. It will be a good idea to connect them to add strength and rigidity. I chose to take the simple path and cut a few PVC pipes to the length of my frame, drill holes on each end and then zip tie them together.

You can get fancy and use pipe fittings to connect the hoops to the horizontal braces, but that will involve a lot more measuring and cutting.

Adding the Greenhouse Plastic

Remember, “measure twice, cut once.” I had to use a strip of duct tape to close the plastic back up because I didn’t listen to my grandpa’s advice!

Unfold the plastic sheeting, drape it over the hoop frame, and line up the sheeting on one side first then tack down and fold the sides. We opted to fold the corners like you’re wrapping a present.

We used a combination of staples and sections of 1x1s to tack down the plastic. The staples were used first to get the plastic in place and then the 1x1s were screwed in strategically to secure the plastic against the inevitable winter elements. Wind is strong!

Installing Hinges and Handles on the Greenhouse Base

After you have an assembled hoop house frame, you’ll want to be able to open it to access your gardening area and to crack it open if it gets too warm out.

I went to my “stock” of hardware that I collected over the years and found some random handles and hinges. You will just want to make sure they’re of sufficient quality and sizing to stand up to the weather and weight of the frame.

Securing the Greenhouse to the Garden Bed

Attach the hoop house frame by securing the hinges to the garden bed.

It will also be a good idea to put a safety chain, rope, etc. to prevent the hinged hoop frame from opening too far if it catches a gust of wind, excessive strength when opening, etc. (we just used some string we had).

Keep a stick handy to hold the frame in the “up” position while you’re tending to the garden.

You will also want a system to keep the frame “closed” to keep the wind from blowing it open. A variety of methods can be employed such as tying the handle to a spot of the garden bed frame, using weight in some capacity, or using some sort of latching hardware. We opted for the latter and used a latch from my “stock”.

Final Touches to the Greenhouse

Examine how the frame sits on the garden bed and make sure there aren’t too big of gaps between the two surfaces. If a large gap does appear, try applying some foam weather stripping.

Maximizing DIY Mini Greenhouse Efficiency

There are a few things you can do to help keep your greenhouse functioning well all winter. When you build the frame, make sure it is in a sunny area to maximize warmth light during the shorter days.

• You can use mulch or straw inside the bed for extra insulation
• Make sure you regularly open up your winter frame on sunny days to vent in order to prevent overheating or mold
• Check it once a week for holes, tears, or rips (use duct tape as needed)
• If you get a lot of snow, remember to clean off the greenhouse so it doesn’t cave in

Optional Greenhouse Upgrades:

• Venting
• Thermometers
• Insulation
• Weather stripping

Types of Plants that Thrive in Cold Frames and Greenhouses

• Vegetables: beets, broccoli, peas
• Greens: lettuce, kale, spinach
• Herbs: cilantro, basil, rosemary

Get ready to roll up your sleeves and create a cozy winter home for your plants that’ll make your neighbors (and your lettuce) green with envy! Let us know if you have a DIY winter frame or greenhouse, we would love to see them!

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