Raised Bed Garden Extended Growing Season

Build a raised bed cloche in 8 steps

 Learn to construct a covered raised garden bed in 8 easy steps, for around $200.

Sam Angima and Bill Biernacki, Oregon State University Extension  TEXT COPYRIGHTS. Jan 2013

Extend the growing season

A cloche is a glass bell jar that is set over individual plants, acting as a mini greenhouse and extending the growing season,

especially in cooler regions. This raised garden bed is built with a cover, essentially a cloche that covers an entire bed!

It is best suited for growing tomatoes, peppers, eggplants, melons, and other crops that need to be planted after danger of frost and generally mature late in the season.

Follow these directions to build a structure approximately 8 feet long and 4 feet wide at the base, and 5 feet high at the center.

Adjust the length by increasing or decreasing the length of the boards and number of PVC hoops, and alter the length of the polyethylene plastic appropriately.

The cost for materials is about $150-$250.

Gather your materials

Before you begin, compile all your materials. Label the boards as indicated.

• 2 A boards: 2-inch x 12-inch x 8-foot boards, treated with water-based preservatives
• 2 B boards: 2-inch x 12-inch x 4-foot boards, treated with water-based preservatives
• 3 C boards: 2-inch x 4-inch x 8-foot boards, treated with water-based preservatives
• 8 D boards: 1-inch x 4-inch x 10-foot boards, treated with water-based preservatives (to be cut to fit)
• 1 piece of 6-mil polyethylene plastic sheeting, 9 x 10-foot wide (cloche sides)
• 2 pieces of 6-mil polyethylene plastic sheeting 5 x 5-foot (cloche ends)
• 3 10-foot lengths of 0.75-inch schedule 40 PVC (hoop supports)
• 1 rubber bungee cord, 18 inches long
• 20 schedule 40 PVC clips (see Step 4/Detail. Obtained by sawing off one-third of a section of 1-inch PVC)
• 0.5 lb (approximate) 3-inch galvanized or stainless steel screws
• 0.5 lb (approximate) 1.5-inch galvanized or stainless steel screws
• 12 0.75-inch galvanized pipe straps
• Hand saw
• Appropriate screwdriver (preferably a power drill)

Step 1: Build the frame

Attach the two B boards to the ends of the two A boards using 3-inch screws at each end.

Cut six lengths of 11.5 inches each from one of the C boards and attach them to the inside of the longer side of the cloche frame you have just made. 

Use 3-inch screws to attach one 11.5-inch board in each corner and one on each side,

centered in the middle and flush with the bottom. These short pieces will support the corners and serve as anchors for the PVC ribs.

Option: Add support to the corners

You may add outside corner metal straps to the corners to further stabilize the raised bed base

Step 2: Add PVC hoops

Slowly bend each of the three 0.75-inch, 10-foot PVC hoop supports into each corner and one in the center to shape the arch of the cloche.

Secure each hoop flush at the bottom of the anchors using the 0.75-inch pipe straps and 1.5-inch screws.

Detail: Pipe straps

Use two galvanized pipe straps on each side, making sure ribs are vertical.

Instead of using pipe straps, you can attach sections of 1-inch PVC pipe to the anchors and just insert and

anchor the0 .75-inch hoops into these sleeves if you prefer.

Step 3: Build the backbone

Lay one of the D boards across the top of all three hoops, creating the top backbone and support of the cloche.

Check that the backbone is level and that the three hoops (ribs) touch the bottom of the backbone.

The ribs can be adjusted by loosening the pipe straps and making the necessary adjustment.

Measure the height of both ends of the frame from the bottom of the frame to the bottom of the backbone to make sure they are equal. 

You will use this information in the next step.

Step 3, continued: Build the backbone

Cut two C boards to the length measured in the last step (approximately 51 inches) and attach them to the outside of each end,

centered and flush with the bottom of the frame (B boards), using 3-inch screws. Cut the backbone to make its ends flush with

the C boards just placed (approximately 8 feet, 4 inches).

Attach each end of the backbone, flush to the outside of both vertical C boards, using 1.5-inch screws.

Check to make sure each PVC hoop is vertical and secure with a 1.5-inch screw down through the backbone and rib.

The remaining seven D boards can be cut to the same length as the backbone.

Step 4: Cover the ends

Open, spread, and attach the 5x5-foot plastic sections of the 6-mil polyethylene plastic sheeting to both ends using the

PVC clips, five on each side. Make sure the plastic covers the entire end, and tuck the plastic against the inside of the frame.

Detail: Make PVC clips

Make the PVC clips by sawing off a third of a section of 1-inch PVC. Pull plastic tight and make adjustments,

being careful that clips do not dig into the plastic. Trim extra plastic but leave a good 6 inches of excess.

Detail: Trim as needed

The plastic should be tucked against the end of the frame and trimmed to fit.

Step 5: Add the top cover

Drape the 10'x10' piece of 6-mil polyethylene plastic sheeting over the hoops, making sure each end and the

bottom sides are even. Do not trim excess plastic until later.

Step 6: Secure the plastic

Place another D board on top of the backbone, sandwiching the plastic between the two, and screw down using 1.5-inch screws.

Step 7: Hold the sides in place

For the side plastic curtains, use one D board on the inside of the plastic curtain and another on the outside,

sandwiching the plastic in the middle. Screw the D boards tightly together, resting on the frame, using 1.5-inch screws.

Curtain should hang with no slack. Trim excess plastic, leaving 6 to 8 inches of overhang below the sandwich assembly.

The overhang prevents rain from entering the cloche. Repeat on the other side.

For more wind resistance, you can wrap the plastic once around the first D board and then sandwich it with the other D board.

You also can attach a hook to the outer D board at each end and two hooks to the frame.

Attach bungee cords between the two hooks to prevent wind from flapping open the curtain.

Step 8: Finishing touches

For added strength and support, attach a D board to each rib (or hoop) on each side about 10 inches down from the

top of the backbone using 1.5-inch screws.

Attach the rubber bungee at the top center of the cloche.

When the side curtain is rolled up, the bungee will hold it in place.

Detail: Opening the cloche

Attach the bungee cord at its center to the backbone.

This will hold the rolled-up plastic for easy access to both sides of the raised-bed cloche.

One last tip

The cloche can get very warm on sunny days, especially. You may want to cut and leave open the top 6-12 inches of each end to allow for ventilation.

Photos and text copyright Oregon State University. Used with permission from Angima, S., and Biernacki, B. 2008.

How to Build Your Own Raised-Bed Cloche.

EC 1627. Corvallis, OR: Oregon State University Extension Service.