My DH would probably place a tarp over the shelves and duct tape along the floor line to keep the water out, and then power wash the bejesus out the floor.

You can try using muriatic acid. You can get it at any hardware store. Be sure to have the garage well venitlated and wear a mask. Pour some of the acid on the floor, use an old push broom or other scrubbing method to scrub it into the concrete. Then hose down-as LisaD mentioned, tape off the wood you'd want to protect.

Make sure not to get any of the acid solution on plants. It will burn your skin, so be sure to wear gloves. It's not like hydrochloric acid in that it will burn holes into you, but it is a powerful irritant, like bleach. It's used to clean swimming pools. My DH uses it to clean his concrete molds after he pours.

Krud Kutter, concrete cleaner

Someone recommended Pine Sol to me for my backyard concrete patio. I have the bottle here but haven't had the time yet to test the theory.

I've had good luck with my outdoor concrete patio with outdoor bleach and a good deck scrubber. ETA I would think Pine Sol would be trouble down the road because of the oils in it, artemis.

Thanks. Never thought of using the steamer and I have a large commercial grade one that I just had repaired!

Steam and good brush is the best if you have access to it.

My DH swears by Simple Green to clean almost anything. It is a bit sudsy and must be rinsed, so go easy on the amount used. I have used it to clean our covered back porch and it does a great job. I just put on my rubber boots on a nice day and go to it with the hose and a long-handled scrub brush.

Thanks, writersblock. I'll try some of these other suggestions first.