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The 14% is elemental copper by weight, which is the guaranteed-analysis figure. The other 86% is mostly the EDTA chelate itself, the molecule that wraps around each copper ion to keep it plant-available, along with associated water bound up in the structure. Guaranteed analysis only lists the active nutrient, so water and the carrier molecule aren't broken out on the label (this is standard across fertilizers). So that 86% isn't inert filler, it's the chelating agent doing the work that makes this outperform copper sulfate, especially in higher-pH soils.
The guaranteed analysis is also regulated by the California Department of Food and Agriculture. We can only list the nutrients we're registered to guarantee, so we can't add the chelate or water portion to the guaranteed analysis even though it's part of the bag.
On mixing: the application rate refers to the weight of product taken from the bag, not a back-calculated copper-only weight. Fertilizer rates are always expressed as the actual bagged material you measure out, and the 14% copper content is already built into the recommended rate. So when you measure a given amount of the Cu-EDTA powder, you're measuring the product as-is, no need to convert it to elemental copper. Just follow the rate as the weight or volume of powder you scoop.
