Because wave petunias are a low-growing ground cover, they do not naturally form a tree. But you can create a petunia tree by placing a container or hanging basket at the top of a tree-like planter.
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Measure and mark 50 inches from the end of the 10-foot PVC pipe. Cut this length off of the pipe with a hack saw. Attach the coupling to the threaded end of the 50-inch PVC pipe.
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Dig a hole just deep enough to put the PVC pipe in with the coupling side up. Cement the pipe into the ground with the coupling exposed and facing upward. Allow the cement to dry before proceeding.
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Insert the hex bushing into the top end of the PVC pipe and weld it into place using a stick welder. You can rent a stick welder at any equipment store.
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Measuring from the base of the PVC pipe, weld nine of the 1/2-by-1 1/2-inch pipe nipples onto the PVC pipe at a point 28 inches from the base.
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Measure from the first set of pipe nipples by 14 inches. Attach a second set of seven 1/2-by-1 1/2-inch pipe nipples onto the PVC pipe. These should be offset from the pipe nipples below them. Attach the remaining five nipples to a point 7 inches above the second set. Offset these nipples from the second row. Attach the 1-by-1 1/2-inch pipe nipple into the hex bushing in the top of the PVC pipe.
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Place a 1/2-inch coupling into the end of each pipe nipple. Place the shorter lengths of PVC pipe into the couplings. The longest lengths of the pipe should be on bottom row with the shorter ones on the second row. Place street elbows on the end of each pipe piece.
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Drill a hole in the bottom of the 12-inch pot with a masonry bit. Attach the 1-inch-diameter floor flange to the 12-inch pot through the hole. Drill holes in the sides of the pots using the masonry bits. Attach 1/2-inch floor flanges to the 10-inch pots through these holes.
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Connect the 12-inch pot to the top of the tree structure using the floor flange and two 1/4-inch screws and nuts. Attach the 10-inch pots to the side branches of the tree using the floor flanges, screws and nuts.
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Spray paint the tree black. Allow the paint to dry. Fill each container with potting soil and place five petunia plants in each 10-inch pot and seven petunia plants in the 12-inch pot.