Grassy poop stuck in hens rear end? Gross pic!

[Wyorp Rock]

I would absolutely start offering grit free choice all the time. Eating too much long, fibrous grass can cause blockages. Some environments have lots of small rocks and pebbles and they are able to find enough, but some do not. It's not very expensive and better that it's there if they need it since not having enough can cause some serious problems. If they are getting the grass in an area that you can mow, then keeping the grass shorter is a good idea too.

X2

I agree with @coach723

imho - it never hurts to make poultry grit (crushed granite) available free choice. This includes making chick grit available in your brooder as well.
A bag of grit will last a long time - I occasionally scatter some in the run and have a small cup attached to a post - they can get what they want. Even if a chicken has access to soil, they still may not find small rocks/pebbles hard enough or suitable to use as grit.