Adam Clarke on Judges 16:11

If they bind me fast with new ropes - Samson wishes to keep up the opinion which the Philistines held; viz., that his mighty strength was the effect of some charm; and therefore he says, Seven green withs which had not been dried; new ropes that were never occupied; weave the seven locks of my hair with the web, etc.; the green withs, the new ropes, and the number seven, are such matters as would naturally be expected in a charm or spell.