Full disclosure: this might be a terrible idea, but it is what I would try.

I would dilute some bleach in a bucket of water and take a wide shop broom with stiff bristles and just scrubs the rocks. Too much and you might actually bleach the rocks (again complete conjecture), so go easy at first.

Good luck and let us know how it goes.

It'll just grow back. You can't win the fight against Mother Nature. Your efforts are futile wheel spinning and would best be spent elsewhere.

A friend of mine cleaned the bulk of it off (pine needles, leaves, etc.) and then used a hose, and then a pressure washer. He replanted in some crevasses. From what I've seen it has stayed very "clean". His lot must have been more wooded, and now that the lot has been cleared the area is more sunny and open.

I would spray it with a 5-1 water/bleach mixture (using a regular pump sprayer, like what you use to spray plants), let it sit an hour, and then pressure wash (wear eye protection!).

Thanks everyone we'll give those a try. :0)

The guy who built our stone retaining wall and put random small boulders around the lot told me what to clean them with (bleach maybe, not sure) and then said they could be sealed (deck sealer???). I've got it written down somewhere, but things are too disorganized right now to find it. I realize this is little help, but my purpose in mentioning that it's possible, is that if you call a place that sells boulders, they may be able to tell you specifically what to do.

Anne

The Landscape Forum is notorious for being unfriendly--there seem to be a lot of professionals that don't want free advice given out since it takes away business for local landscapers, or they expect you to have read a lot about landscape design (their books?) before you ask a question, or something!

Try the link below. Don't know if they can answer your question, but I've occasionally been on several of the other gardening forums, and people over there are, for the most part, very helpful. Just stay away from Landscape!

Anne

Here is a link that might be useful: Gardening with Stone

You're kidding, right???? The moss doubles the value of the rocks, at least, and most people adore the look--hence the rock-robbers who used to come into my old neighborhood to try to steal genuinely lichenous (too dry for moss) rocks from our yards.

Yes, they pay big money in our area of the country for "moss rock"

No I'm not kidding. Some people like moss and some don't. I'm not worried about the value of the rocks, we want to enjoy the beauty of them. We like to see the veins and colors of the rocks. The rock has been cut thru (like when they make a road/highway) when they built the house I guess to make some what of a backyard so you can see the different layers within the rocks which is interesting and beautiful.

I now these posts are old, but I know the same questions come up. Which, is why I'm on here now... Just wanted to say that I have a area with all of my 'special rocks' which were getting a lot of mildew on them and black spots. I spent quite some time a few years ago taking large buckets of water and put a good amount of bleach in it and adding the rocks. I'd let them set in this water for usually overnight... then put on gloves and use a cloth or brush and just easily wash them down. They were beautiful when I got done and stayed acceptable for about 3 years... now they are beginning to look like they need another bath.

U could try lemon lemon juice vinger or baking

1. This thread is over nine (9) years old;

2. Anyone interested in rock cleaning can visit their nearest prison.

That prison idea is creative but the hosts there are quite mean about letting out their guests to do useful work. Their specialty is breaking rocks, but they might do well.

HU-9... seems to have a good idea: bleach, leave overnight, wash off. I'll try.