Woops! Brilliant recycling but it is jute string which decomposes when damp for any length of time… I remember my father being so happy when he could tie his bales with more enduring, polypropylene string, even though it is of course now a waste problem for most farmers.
You could tie the exisitng string loosely to the bottom of each stem, I did that once and it was fine. In fact I have just done the same for a few climbing french beans.
Well done on growing and selling lots of salad in your first season. The hardest thing is to match supply and demand!