I think they would just stay there rusting, you could take them to metal recycling?

They help to turn pink hydrangeas blue, other than that, none that I can think of.

Thanks for the information
Pat 1.

I wonder if they would keep snails and slugs away from tender plants and seedlings if you sprinkled them in good measure around the plants you wanted to protect?

i tell you what they are good for.if you dip them in salt water and take them out a few times then do a runny cement mix with plenty in and coat something pottery or cement in it it will run rusty and looks realy smart.

If the soil is alkaline, they will just rust without releasing enough soluble iron to help anything. Try mixing them with dusting sulfur before spreading them--that will turn at least some of the iron into copperas.

I'm about to apply them to ericaceous raised bed and around garden generally. I have used old bolts and rusty nails in the past, as well as wrought iron decorative items for this purpose.

I find that as I regularly use diluted distilled vinegar all around the garden - except on my Calciferous raised bed - in order for it to break down clay, the by-product is it makes iron sources more bioavailable.

(If you take a small bowl of coir, add iron particles and a little water, after about a day or so the bowl will heat up due to micro-organisms coming to life and generating heat.)