How long will the grass/plants in the run last?

[Mrs.ChickChick]

Just moved my girls to their new coop and run. Their run is 10 feet by 20 feet, and I have 8 seven week old girls. There is grass, flowers, and plants in their run, but I know these probably won't last long. Should I expect a mud-pit anytime soon, or will it last through this summer?

 

[Uppity Peon]

My original coop area was originally about 12'x8' and when I released 23 4 week-old chicks the grass had no chance. It seems it was all gone in less than a week. I later added a 12'x12' side yard which still has grass, although they have some dust-baths excavared. Then I added a 12'x45' run which still has plenty of grass. They still prefer the smaller side yard because it is well shaded by trees. Hopefully this will give them plenty to browse on until they are grown up enough to run around free in the 1/2 acre back yard.

The chicks are 9 weeks old now.