Vegetables Gardening - Growing Organic Vegetables

Hopefully just about anyone should be able to answer this as you are all growing successfully.

I have just mixed my first mix of pre-plant and of weekly feed. I am applying it to my orchard and fruit bushes while I get my garden beds built up correctly.

I had no problem with the pre-plant mix because the Lime, Epsom Salts and Sodium Tetraborate (Boron) are all about the same granual size so stay evenly mixed.

I have a slight distribution problem with the Weekly Feed. The mineral mix is much finer than the triple 15 NPK granuals which are a standard size (£9 for 25kg / $13 for 55 lbs from my local farm feed store) so falls down through it in the container so that nearly all the fine mineral mix and Epsom Salts are down at the bottom of the container while the NPK is above it. I mix it up and it falls through again. If I try to take a 'serving' in a can I either get nearly all NPK if taken from the top or 50 % mineral mix if I take from the bottom. How do you go about ensuring the mix stays evenly distributed given the size difference of the granuals and the laws of physics?

Hope someone can explain what I am doing wrong, no doubt it is something blindingly obvious that will make me feel stupid! Oh well!!!

Thanks in advance.

Bruce