How to Measure for Block Edging for a Circular Garden Bed

Written by beth asher
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Using garden construction blocks for edging has become popular. The blocks come in a range of colours so they can be matched to the house colour and trim. Blocks taper at the rear so they form circles naturally. Widths can be anywhere from eight inches for cobbles to 17 inches for retaining wall blocks with the most common width being 12 inches. Once you know the circumference of your bed, (which is the length all the way around) you can easily calculate the number of blocks needed to edge it.

Skill level:

Things you need

  • Measuring tape
  • Stakes
  • Paper
  • Pencil
  • Dimensions of your block
  • Calculator
  • Mason's hammer or brick set and hand sledge

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    Measure the Bed

  1. 1

    Drive stakes in at regular intervals around the bed edge and run the measuring tape along the outside of the stakes to keep it from kinking or bulging out. Write down the measurement. Measuring a circular bed can be tricky, because you have to bend the tape measure.

  2. 2

    Measure across the middle of the bed to get the diameter and write down the measurement. Using the diameter (the distance across the centre of the circle) to calculate the circumference is another way to get the figure you need--this is the first step in doing it this way.

  3. 3

    Multiply the diameter by pi (3.14) and you have the measurement around the outside of the bed. For instance, if the bed measures seven feet across, 3.14x7 equals 21.98, so your bed is roughly 22 feet around.

  4. 4

    Convert the feet to inches to determine how many blocks you will need. For example, if each block is eight inches long, 22 feet x12 inches equals 264 inches, and 264/8 equals 33--so you will need 33 blocks..

  5. 5

    If the number of blocks you need turns out to include a fractional block--16-1/2, for example--you have two options. Look for blocks that have matching half and quarter block cobbles or use a brick set and hand sledge to score and break blocks to size.

Tips and warnings

  • Use the cap stones designed for retaining wall blocks if edging is not sunk into the ground to create a finished look.
  • Use a base of crushed rock for your edging to prevent frost heave.
  • Blocks can be sealed to prevent the growth of moss and algae.
  • Buy two or three extra blocks if you will have to do any cutting to fit. This allows for breakage and ensures that coloured replacement blocks will be from the same dye lot.
  • Blocks sunk till their tops are level with the surrounding soil may become covered over time or encroached on by weeds and grass.
  • Level the ground and remove grass and weeds before laying blocks.

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