If they are just tossed on the top of a bed, that would be unsightly and it is doubtful their nutrients could get to the roots of a plant.

In the summertime, I save crushed eggshells, teabags, coffee grounds and filters plus other kitchen trimmings in a bucket with a lid and place it outside on the porch. When it gets full, I pour in a little water and then pour it around Louisiana clumps. Later in the fall, I cover it all with pine straw. Surprisingly, it draws few flies. I think the coffee does something to drive away the flies.

I don't do this in the winter. I may put some stale bread out for the birds but that disappears fast.

Walter Moores

I will ask my mom to crush the eggshells before "topdressing" the beds. I was mainly concerned whether or not the shells would be bad for the iris. Thank you!

Eggshels, crushed, supposedly will help lighten clay soils. My experience is that would take a lot of eggshells!

In an excellent book the author says burning the eggshells will allow their nutients to be available to plant roots. Otherwise it takes several years for them to break down.

Some people think that surrounding new plants with crushed shells deters slugs/snails.

I still dig them in.