I just had my yard hydromulched. The mixture that was used was pretty heavy and thick. We got a lot of rain after it had been down for about 8 days. None of mine washed at all. I may have gotten lucky as far as that goes. I did have to water it for 15-20 minutes twice per day for the first week. Then once a day for a week after. Now I just water every other day. 3500 square feet and it looks great. It was a mixture of bermuda and centipede. The bermuda came right up and the centipede will take most of the summer to come in and start taking over. I spent about $225 less than I would have if we had sodded, and I didn't have to pick it up and haul it, or lay it. My experience was good, but like I said, I may have hit it at the right time.