Crooks, I'm not 100% sure if there is enough salt left on rocks & things gathered from ocean beaches to bother plants
, but I think that rinsing them off wouldn't be a bad idea.
Years ago, I hauled a lot of kelp home from the bays in Seattle Washington & buried it in my garden, & my vegetables grew like crazy! I've also crushed up clam shells & put that in my gardens, & have decorated garden beds with driftwood found on ocean beaches... (there was plenty of salt content in that stuff, & at the time I hadn't even thought about it having a bad effect of the plants... or I probably wouldn't have done it!)
(We'll want to see pics when you get done with your project, you know!)