[Nick36]

Hello everyone.  I am quite new to gardening, and i am a little confused about the N.P.K ratio's.
If i added an N.P.K. ratio of 5.5.5 to a 0.10.0 ratio, would i have 5.15.5?

[DavidT]

Nick you are over complicating things. You need to learn what the nutrients are, and what they do.
N = nitrogen, used for leaf developement so ideal for the likes of cabbages and members of the onion family. The higher the N level, the more benefit to leafy plants.
P = phosphorous ( phosphates ), used for root developement. Perfect for root crops such as potatoes, carrots and parsnips. A good fertilizer to encourage a good root system for ALL plants.
K = potasium ( potash ), essential for the the developement of flowers and fruit. Needed for All flowering and fruiting plants. 

[gillie]

If i added an N.P.K. ratio of 5.5.5 to a 0.10.0 ratio, would i have 5.15.5?

Not necessarily.  It would depend on the ratio of the two fertilisers you mixed together as well and whether they contained any fillers.

As DavidT says, make it too complicated!  Buying a good general fertiliser will do for most things and use it for what it says on the  label.

Gillie

[Ivah]

You would actually have 2½-7½-2½. Might be OK on Brassicas if you thought they needed a Nitrogen boost. Generally equal NPK contents are easiest to use, possibly with a bit of extra P for roots (eg Potatoes) or extra K for fruit (eg Tomatoes). Blackcurrants are bit of an exception and like a bit extra N.

[BostonInbred]

the numbers are the active percentages.

The problem with mixing is that 5:5:5: means theres 5% active nitrogen, 5% active phosphorus and 5% active potassium.

The point where your maths goes wrong is in the word ACTIVE.

I might have a nitrogen donating substance where 20% of the Nitrogen is available. so to make my balanced fertiliser 5% active then each KG of 5:5:5 has  (5/100)/0.2 = .25Kg

The Nitrogen donating substance in the other fertiliser might only have 10% active component, so we would need  0.5Kg per Kg fertiliser.

The snag is that mixing one with the other does not add them together, because the proportion in each bulk is different, and what you would end up with by mixing even equal amounts together is about 7.5% nitrogen active component.

Mixing a fertiliser to get the active components correct is not an amateur hobby!! Thats what people like Bayer got rich doing it!!


So the maths might work in some cases, but in a lot of cases the result will be very unpredictable.

[solway cropper]

I'm curious about the 0.10.0 fertilizer. What is it?

All I can think is some sort of phosphate and that would be for a different purpose and applied at a different time. Like the others, I'd say don't mix fertilizers as they tend to be formulated for a specific purpose.

[Salmo]

The 0-10-0 fertilizer is probably rock phosphate. This is ground up unprocessed rock and is counted as organic. It can vary between 3 and 10% phosphate depending where it comes from.
As with all fertilizers the stated 10% is the soluble phosphate available to the plant. It is in fact probably about 35% phosphate but it is mostly insoluble. However, if it is used on acid soil the acid makes the rest of the phosphate available over a few years.

The big breakthrough in agriculture was the manufacture of superphosphate, often referred to by gardeners as supers. Many of the older Fenland farmers refer to all fertilizer as 'fossit' , a term which I presume stems from superphosphate which was the first widely available inorganic fertilizer. Superphosphate is produced by treatiing rock phosphate with sulphuric acid. It is 21% phosphate of which most is soluble and available to the plants.

A further development was triple superphosphate which was produced by treating supephosphate with phosphoric acid. It contains 45% phosphate which is almost all available.

So much for the history of fertilizer. I am sure you can apply both of these to the same seedbed but I would not mix them together in the same bucket. It would probably cause no problems in this instance but mixing things is not a good habit.

The answer to your question is that if you put the recommended rate of 5-5-5 on and then followed with the recommended rate of 0-10-0 you would have applied  the equivalent of 5-15-5.
i.e.
4oz per sq yard of 5-5-5 plus 4oz of 0-10-0          = 5-15-5
but 4oz per sq yard of the two mixed together = 2.5-7.5-2.5     

[yorky]

4oz per sq yard of 5-5-5 plus 4oz of 0-10-0          = 5-15-5
but 4oz per sq yard of the two mixed together = 2.5-7.5-2.5     

Thanks for that Salmo. My head was starting to spin trying to keep up with this topic, but you seem to have summed it up in a nutshell.

[Snoop]

I have been struggling over fertilisers in recent days.  John has some very useful information that has proved invaluable for me, but I would love to learn more. Are there any useful books you could recommend on fertilisers for allotment holders? I'm not a chemist and a newbie to vegetable growing.