Measure the area of your plant bed. You want to ensure that your landscaping timbers are the right length for the job. If your timbers are too long for your flower bed, cut them down to size.
Dig a ditch around your plant bed that is the width of the timbers and at least three to four inches deep. The depth of the ditch will help secure your timbers in place. You may want to line the ditch with plastic to prevent weeds from sprouting.
Lay the timbers into the ditch. Place the end of one of the timbers at a corner of a the ditch. Lay timbers at a 90-degree angle to create corners. Ensure that your corners are flush. Lay additional timber above the base timbers to create a second level. Stagger placement of the second row of timbers so joints do not line up. This will increase the stability of your border.
Drill short holes every four feet in your top row of timbers. Do not drill all of the way through. Hammer a 12-inch spike into each hole you created. The spike should reach all the way through to the bottom timber, effectively joining the two. Continue laying out the timbers and nailing them in this fashion all around your plant bed.