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How to Build a Planter Box for Dahlias

Dahlias may present more effort than marigolds or daisies, but if you grow them successfully, they’re worth the work. Dahlias are finicky and require certain moisture levels and soil temperatures. The plants will die if the soil is soggy or the ground is too cold, which is why creating your own dahlia planter is a good idea. You can build the planter to dahlia specifications and control the flowers’ environment by moving them as necessary.

Things You'll Need

  • Five 12-inch square tanalized wooden boards, 1 inch thick
  • Two 12-inch tanalized boards, 1 inch wide by 1 inch thick
  • Electric hand drill
  • Wood screws
  • 1/4-inch diameter drill bit
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    • 1

      Lay one of your 12-inch square tanalized wooden boards in front of you. Place a 12-inch-long wooden board along the left and right edges of the 12-inch square board. Screw the 12-inch-long boards into place, creating rails on the square board. Tanalized boards are treated with tannins to keep them fresh for longer periods of time.

    • 2

      Flip the railed square board over so the rails act as legs. Line the bottom edge of a second square board with the bottom edge of one of the rails.

    • 3

      Screw the bottom of the square board directly into the rail. Repeat on the other three sides of the square board, creating a box. This box is roughly 12 inches wide and 11 inches deep on the inside. Dahlias need at least 6 inches in all directions for their tubers to grow, so this gives you plenty of room to layer drainage gravel in the bottom before planting the flowers.

    • 4

      Screw the side boards together at the corners, using at least four screws at each corner.

    • 5

      Flip the planter upside down. Drill four rows of 1/4-inch diameter drain holes, spacing the holes and the rows at least 2 inches apart. This allows excess water to drain, keeping your dahlias at the right moisture level and preserving the integrity of your planter box.