Chair cushions can slip, especially on lawn furniture. Ties are not only decorative, but also keep a cushion from blowing into the yard on windy days, or simply keep it beneath someone using the chair. Of course, the chair must have openings for the ties to go through and around as most lawn chairs do. If a chair cushion's tie has torn, or the cushions never had ties, you can make ties and attach them easily.
Cut the fabric into strips. Each tie will be in two pieces. Each piece will require two strips of cloth for the front and the back. So to make one tie, cut four strips of cloth. The actual dimensions are based purely on your preference for long verses short ties and for thick verses thin. For something semi-standard, cut the strips approximately 12 inches long and 3 inches thick.
Sew a pair of strips right side together along three sides, leaving open one of the 3-inch sides. Then turn the strip inside out, so the seams are all on the inside. This is half of a tie. Repeat this process with another pair of strips and you'll have the makings for one tie.
Use the seam ripper and carefully open the seam near one corner of your cushion, where you want the tie. Open the seam enough to insert the end of the ties.
Insert the raw ends of both tie strips into the opening in the cushion and sew it back shut. If the cushion covering can be easily separated from the padding, you can take the cushion apart and sew on all the ties at once with a sewing machine. Then turn the cushion right side out and restuff.
Repeat the process for as many ties as you wish to use.