If you've got the rocks, you can turn them into an attractive border for your flower beds with a little mortar and some muscle. If you've ever assembled a jigsaw puzzle, you can probably manage laying out an attractive stone border. Mortar works a lot like glue. Pour it into the cracks and crevices and wipe off the excess and you have a sturdy flower bed.
Mark the outlines of your flower bed with wooden stakes and strings. Drive wooden stakes outside the string line every 12 to 16 inches. Drive a second row of stakes inside the outside string the width of the border you want. If you want a 6-inch border, for example, drive the stakes 6 inches apart.
Dig an 8-inch-deep trench between the string lines. When completed, pour 3 to 4 inches of sand into the bottom of the trench and smooth it flat with a rake.
Nail 1-by-4 inch boards to the stakes with form nails. The sides should be parallel. Nail a short piece across the ends. Make sure the tops of the parallel frames are level.
Lay out the stones you've selected for your border. Border flagstones should be long and thin. Lay out the rocks inside the trench on top of the sand. Press the irregular bottoms of the stones into the sand and raise and lower the tops to make a level surface. Even if you go for an irregular border, the tops of the stones should line up with the top of the form boards and fill the space as much as possible. Continue around the border until you've laid all the stones in place. Use a rock hammer to knock off the edges of stones that don't fit well in the space you have. Make the spaces between the stones as narrow as you can. Stagger the ends so they overlap.
Mix mortar mix in the wheelbarrow. Mix only as much as you can use in 10 to 15 minutes so the mortar doesn't set up on you. Make the mixture thin enough to tamp between the stones.
Scoop the wet mortar onto the trowel and slip it into the spaces between the stones starting at one end and working your way down the border. Use the tip of the trowel to push plenty of mortar into the spaces between and under the flagstones. Pat along the seams and spread the top of the seam flat. As you finish a section, gently hose off the oversplash from the top face of the flagstones.
Remove the form boards once the flagstones are set. Wait about 24 hours at least. Push dirt up against the borders to fill in the edges around the border. Fill the flower bed with mulch and soil and plant.