Yes, grit is absolutely necessary when they eat grass so they should have it available at all times. If they are picking the grass themselves, and they have grit, they’ll be fine. Grass is an impaction hazard only when allowed to get long and then cut, so the chickens consume very long whole strands, as opposed to picking pieces off the top little by little when they graze. With long grass strands grit won’t help prevent or clear up an impaction, because the impaction is in the crop and the grit is in the gizzard, different parts of the digestive tract.
