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There are a number of benefits to building a covered raised bed in your garden: it serves as a physical barrier to keep pests away (from rabbits to leek moths); it can extend your season by offering a shade cover; and it can keep your garden bed more organized for easier spring prep.
Over the past few years, we have been building 1-2 covered beds each year by combining a simple raised bed frame with a small tunnel set up. The equipment is simple, the cost is reasonable, and the rewards are many.
With these covered beds, we can start our salad greens and radish earlier, we have finally had success keeping cabbage moths off of our broccoli, and we have saved our onions from leek moth invasions.
The supplies for these 16 foot raised beds with covers cost about $70-80, and it takes about one hour to put together one bed with a few simple tools.
Supplies (for a 16 foot bed):
5 2x6x8 pieces of Garden-Safe Lumber - we used heat-treated wood; do not use pressure treated in the garden. Hemlock or Ceder will last longer, but those can be expensive so we typically stick with pine or other varieties available for less money.
Scrap lumber to assemble the bed - you'll need some 2x4s to connect the corners and middle pieces of your bed. We always just look around for what's lying about. If you don't have scrap wood, one 2x4x8 should give you plenty to work with. You may also be able to use the extra piece left from cutting down the 2x6x8 for this purpose (see photos).
8 10-foot pieces of 3/4 inch PVC Pipe
One package (20 pcs) 3/4 inch Strap Clamp - we usually use strong plastic clamps
One 12 ft x 20 ft Garden Fabric or Row Cover - we prefer the summer weight garden fabric available from Gardener's Supply. It's important you get the right width to fit over the top of your frame with enough extra to be held down on either side.
Decking screws (32 1-inch + about 20 2 1/2-inch ) - to attach the strap clamps to the bed, and to build the bed itself
Optional: 4 8-ft 4x4s to anchor the fabric on either side. You can choose a variety of anchoring methods from burying in the dirt to landscape staples to whatever extra wood or rocks you have you lying around. We like the 4x4's (we had them lying around) because they are nice and heavy to hold it down, but are also fairly easy to roll aside to access the bed.
Step 1: Build the Bed
The simple set up for this bed entails connecting two 2x6x8s for each of the long sides of the bed, then cutting one of those 2x6x8's into 3 foot pieces for the end of the bed. You use a strip of scrap wood on each side to strengthen the connection in the middle, and a chunk of wood in each corner to stabilize the corners.
Step 2: Install the Strap Clamps
This bed uses 8 bent PVC pipes to support the cover. Thus, we space the strap clamps so that the first PVC pipe on each end is about one foot in from the end of the bed and the clamps are 2 feet apart. In other words, you'll attached a strap clamp at 1 foot, 3 feet, 5 feet, etc. Each strap clamp is attached with 2 decking screws.
Step 3: Insert the PVC Pipes
We've measured our beds to fit the 12 foot wide garden fabric, using the full length of the 10 ft. PVC pipe. If you're garden fabric is not as wide, you may have to cut down the pipe for a smaller fit. Simply insert the pipe on one side of the bed, bend, and insert into the other side. It should be a fairly snug fit so and the ends should be pressed slightly into the soil so that the arch will not fall to one side (although sometimes the ones on the end will simply do that naturally and it doesn't effect the stability of the cover).
Step 4: Add the Row Cover, and Anchor with your chosen material
Now, simply stretch the row cover over your bed and anchor it with whatever materials you've decided to use (in our case, 4x4's). You can also choose to dig one side of the cover down into the dirt and just anchor down the other side, but this limits your access to one side of the bed which may make it hard to reach things on the permanently anchored side.
That's it! Now plant your lovely veggies and enjoy the rewards!
We'd love to hear if you try this method and how it works for you. Good luck, and happy gardening.