I recall a post where AC said once that you could mix Plant Wash as low as 1/2 ounce per 1 gallon but I cannot find it, and another post I found today said not to go over 1 ounce per gallon because "This is a fertilizer as well as other things. You can actually over fertilize plants and burn them with the Plant Wash."

As Mike said, the general rule for all of AC's products are 1 ounce per gallon. The exception to the rule is the new condensed Green Wash (part number 83-, and I believe AC is working on making most of his other products condensed as well. The price drops a little, but you save a lot on shipping charges. I was going to link it but the J.Racenstein site is having work done, but the part number is 83-642.

For a ball park idea on how much to mix, from another post from AC - I generally use about 30 gallons of mixed Plant Wash on the average 2,500 square foot home.

The label says one ounce per gallon, but anywhere between 1/2 ounce and one ounce per gallon will work.

We use our bulk rinse module to apply plant wash. Easy and much faster.  1oz per gallon.

David