No problem using clippings from grass that was fertilized. However, if they have had any sort of herbicide applied then I wouldn't use them in a vegetable garden.

Rodney

Amen. Residual lawn herbicides in the garden are a chronic problem for many and lethal to many vegetable plants. Even when composted for 6-8 months residual effects remain.

Dave

If you spot treat for the weeds, then just designate an area of the lawn that gets no treatment. Use the clippings from that section specifically for mulch.

It depends on the spot treatment. You mean Roundup? Glyphosate breaks down in sunlight, so glyphosate sprayed on a sunlit lawn is probably gone in a week. Once it gets into the soil, however, it can hang around for a while. I don't think watering has a lot to do with it, though if it is washed into the soil and the clippings below, I guess that could preserve it.

Of course, if you step on the sprayed areas and then step in your garden, it won't be fun.

Suggestion: Get some straw to add around the potatoes and alternate with the grass clippings. You will have a wonderful layer of compost by the end of the season.