Well, if no one is selling the 5-1-3 fertilizer, here's one of the cheapest mix that you can do.

1.45 lbs sulpomag (0-0-22)
3.05 lbs ammonium sulfate (21-0-0)
1.00 lb triple 16 with minors (16-16-16)

The above mix, if accurate as labeled by the packages should give a ratio of 5 - 1 - 3 with a good dosage of magnesium and sulfur as a bonus.

You can obtain all of these fertilizers very cheaply from agricultural supply store. Ammonium sulfate and triple 16 are one of the cheapest fertilizers in the lawn section, just avoid those with the weed killer or preventer in them, they would kill your citrus.

There could be a little challenge when obtaining sulpomag, these are usually mined in Canada and should be very cheap there. They are also mined in the US. You can order these online from www.amazon.com store. Fortunately our local Ace Hardware, OSH and Lowes carries them after being persistent with their customer service to stock them.

In practicality, you would mix 1 1/2 cups sulpomag with 3 cups ammonium sulfate and 1 cup triple 16 and you wouldn't be far off with the 5-1-3 ratio.

Hope this helps.

But as for me, whatever is on sale, or whatever is on garage, or whatever my friends who are moving would left me with whatever fertilizer, I mix and match to get whatever ratio I would like. Bananas for example would demand higher K than N. Stone fruits are the easiest for me, I simply throw away the residuals at them, and they'll take it, because they're planted inground.

The link is gone from amazon about the sale of sulpomag, the fertilizer, not the book.

Anyway, another place is http://www.ebstone.org/21_sul_po_mag.php

but their formulation is 0-0-20
so you would need a slightly different mix:

1.60 lbs of that sulpomag (0-0-20)
3.05 lbs ammonium sulfate (21-0-0)
1.00 lb triple 16 with minors (16-16-16)

Thanks a lot for this very important info Joe.
YOU ARE DA MAN!

Benny

thanks Benny. There are obviously a lot better persons than me when it comes to mixing fertilizers. But I have time to help at the moment, so better put up with me.

I made a formal recipe based on pure calculations and here it is:

link

Being located in farm country, all three of those fertilizers are readily available. I normally purchase a lot of 16-16-16 for use on the farm. Thanks for the information, it is appreciated.

Thanks JoeReal, "Attaining the 5-1-3...." topic is great and much appreciated.

You're welcome fellow citrus lovers! At least I know it helped some of you, and I'm glad to be of help.