Forgive me if this has been answered, elsewhere. I've used the search tool here.

For 3 weeks, I've been hunting for a 5-1-2 soluble fertilizer. At local nurseries, I've found a 3-1-2, but nothing closer. I've found a 4-1-2 slow release which is fine for building potting soil, but still want a soluble fertilizer.

I've hunted the internet, too. Nothing.

Any suggestions? Maybe I could mix up my own...

Mark

Mark, if you are looking for a fertilizer formulation that has the same ratio as the ratio that citrus roots extract nutrients from the soil, then the formulation would have to be 5-1-3. Unfortunately this is a difficult ratio to locate. By addition of Ammonium Sulfate (21-0-0) you can increase the nitrogen ratio of close formulations,

Millet

If you want to achieve 5-1-2 ratio, here's how it's done almost perfectly:

Mix 9 cups of 3-1-2 with 1 cup ammonium sulfate. the ratio would be very close to 5-1-2, and if you are unto near precision, mix 9.13 lbs of 3-1-2 with 0.87 lbs of ammonium sulfate to get the ratio 5.001 -1-2.

For my inground citruses, the 3-1-2 is perfect enough for them.

Mark, it is good that you pointed out the exact ratio of your 3-1-2 source, which is 24-8-16. You could have minors with Miracle Gro which is a good thing. Anyway, the ammonium sulfate is almost a pure form about 99.5% or close to 100%, as there are no fillers when you buy these prilled form. So it is basically 21-0-0.

To get to the 5-1-2 ratio, you needed to mix 0.5675 lb of 24-8-16 Miracle Gro and 0.4325 lb of Ammonium sulfate 21-0-0. When mixed, this would be 22.7025-4.54-9.08 which reduces exactly to: 5.00055-1-2. Practically, one cup of Miracle Gro's 24-8-16 and one cup of ammonium sulfate should bring you very close to 5-1-2 ratio.

(stupid question): could I use blood meal 12-0-0 in place of ammonium sulfate using almost twice as much? I can't seem to find amm. sulfate.
Is there a real diff between the two? Thanks.

Hi Patty, the difference between the 2 is that the blood meal is an organic form on N and will take time to break down and become available. On the other hand it is unlikely to cause the chemical burn that soluble forms such as Ammonium Sulfate.

I don't know it you have farm stores or "seed and feed" stores in your area, but that is where I get mine.

Thanks Skeet, I'll just use what I have for now & in spring take a ride to the boonies.

when it comes to fertilizers, I'm a cheapskate!

So I'm really counting the $ spent per unit weight of nutrients.

For a simplistic example I would need just nitrogen for now and there are two types available:
20-lb ammonium sulfate normally costs $5.99 ($3.98 if on sale!)
5-lb blood meal normally costs $8.99 ($4.99 if on sale!)

With ammonium sulfate, formulation of 21-0-0: the price per lb of nitrogen would be
$5.99 / ( 21% x 20 lb) = $1.42 per lb of pure nitrogen.

With blood meal, formulation of 12-0-0
$8.99 / (12% x 5 lb) = $14.98 per lb of pure N.

You can easily see that the blood meal is 10 times more expensive. But of course, the value of the minors that came with your blood meal could be priceless. You can do calculations when on sale.

Now let us assume that our major elements would have equal weights in terms of importance.
20-lb bag of 16-16-16 costs $7.99.
20-lb bag of 21-7-14 costs $9.99.
And let us say for now you don't care about the ratios, only that we get more bang for the buck of included elements:

The 16-16-16 formulation would cost: $7.99 /([16%+16%+16%] x 20) = $0.83 per lb of element
The 21-7-14 formulation would cost: $9.99/([21%+7%+14%] x 20) = $1.19 per lb of element.

But ratios really matter, and I calculate the nearest equivalent one given the prices to come up with really cheapo formulations. That's where my programming comes handy too often.

But without a programmable scientific calculator when browsing the store, you should understand the trouble and complications I go through whenever I buy fertilizers! Imagine my kids dragging me out the store as I haven't done my calcs yet!

Thanks Joe, I paid too much for the blood meal

Ammonium nitrate used to be the cheapest form of N ($6.50 for 40-50# of 34% N), but the requirement to track all purchases to avoid terrorist using it has increased the price dramatically. I hear that urea is becomming the cheapest form, but I understand there can be problems for citrus if it is not low biuret urea.

How time flies!

A day or two after I got Joe's suggestion for mixing the mythical 5-1-2 water soluble fertilizer, DW proudly brought me a bottle called 'Liquid fish'. It was 5-1-1.

Since Joe had me thinking about mixing stuff, I decided to put a cap full of 'liquid fish' and 2 tablespoons of 28-8-16 miracle gro in 2 gallons of water (my watering pot). This brew would follow 2 gallons of fresh water (spread over 7 3-4 foot trees). I'm guessed this was somewhere near a 4-1-1.5 ratio.

All my trees immediately put out a riot of blossoms. My moro and satsuma had never blossomed, so this was a great pleasure. Both the moro and satsuma have never looked better. They have put out big broad green leaves and look a picture of health.

My two grapefruits put out a lot of blossoms, but decided to drop most of their leaves. New leaves are slowly being added, but the trees look fairly sticklike. The trees just finished producing about 7 grapefruit each.

The clementine and Dancy seemed to put on a lot of blossoms, but didn't do much in the way of leaf growth. Neither looks very happy, but I suspect it is the heat in the greenhouse. Their corner doesn't get the best air circulation. Now that the greenhouse plastic has been removed, I'm expecting them to perk up.

Here is a photo of a grapefruit. The happy moro is in the upper left corner. The horizontal branch in pointing to the bottom left corner has now gone brown (died).