[JayG]

Growmore is a good all-rounder and of course much easier, even though I'd just figured out how to answer your original question!   

[Nobbie]

If like me, you've got a load of woodash, which is apparently 10% Sulphate of potash, I assume you could use this at 10 times the rate? Mind you, on potatoes would it's alkalinity make them prone to scab?

[JayG]

The composition of wood ash varies widely, but I think 10% for potash sounds quite a bit too high.

Calcium, mainly as oxides or carbonates, is obviously not mentioned in an NPK analysis but is by far the biggest component, which does make wood ash quite alkaline and therefore a no-no for ericaceous plants, and not a great idea for spuds either.

[Steve.B]

Growmore is a good all-rounder and of course much easier, even though I'd just figured out how to answer your original question!   

Please go for it, more answers the better....

[Steve.B]

If like me, you've got a load of woodash, which is apparently 10% Sulphate of potash, I assume you could use this at 10 times the rate? Mind you, on potatoes would it's alkalinity make them prone to scab?

sadly we are not allowed fires on our site.

[Salmo]

A popular organic alternative is chicken manure pellets. The problem with this is that it is high in nitrogen and low in potash.
 
From RHS website
Typical analysis of dried and pelleted poultry manure:*
N** (nitrogen)         4%
P** (phosphorus)    2%
K** (potassium)     1%

Typical analysis of Growmore:
N** (nitrogen)         7%
P** (phosphorus)    7%
K** (potassium)      7%

* Actual nutrient content is highly variable
** N as ammoniacal nitrogen, P as phosphorus pentoxide, K as potassium oxide


The high nitrogen will give lots of top growth and is OK for brassicas but not wanted in legumes or root crops.

The low potash is not a problem on clay based soils which are usually high in potash anyway. Over time on light sandy soils the potash levels could become depleted if extra potash is not added. Natural organic sources of potash are difficult to find.

I tend to use chicken manure as a top dressing where nitrogen is needed as an alternative to inorganic nitrogen fertilizers such as sulphate of ammonia or ammonium nitrate. The nitrogen is a little slower acting and the extra phosphate and potash are a bonus.

[JayG]

Growmore is a good all-rounder and of course much easier, even though I'd just figured out how to answer your original question!   

Please go for it, more answers the better....

OK - I wasn't great at maths, even when I needed to be (which was a long time ago), but I think this is correct:

Formula (per 100g of made-up fertiliser): grams of each ingredient =  required %/actual % X 100

For the 6:10:10 potato fertiliser this equates to 29/56/20 grams of the NPK ingredients respectively (total 105 grams)

For the 6:8:15 onion fertiliser it equates to 29/44/30 (total 103 grams)

NPK analysis is based on the proportions by weight, so given that the ingredients are likely to be of different densities they would need to be weighed rather than measured by volume, although it's not an exact science and would probably make no difference in practice - how much you apply, your soil, and the weather will all have a bearing on how it's actually used by your plants.

[mumofstig]

How about BF&B as an organic alternative to Growmore?
It's better for the soil, in the long run.

[Goosegirl]

GG the ex-scientitst here (thanks Snows!)  I, too, find it very strange that you have a reading of zero for nitrogen. I know nitrogen is very soluble and all the rain we've had won't have helped at all but, unless you have very sandy soil as well, you should have a reading of sorts. Not knowing the average percentage that soil normally has, I would first check your tester by sticking it into some fresh manure! Unless you want to go down the route of making your own recipe, I would just go for the simplest option of getting Growmore or BFB then you can add other nutrients as needed for your onions and pots.

[Puenktchen]

Apparently it makes no sense to test your soil for nitrogen levels in winter as most of the nitrogen will have leached out by then (see below). So a reading of 0 for nitrogen makes sense:

"A soil’s nitrogen supplying capacity depends on the microbial breakdown of organic matter and the conversion of the nitrogen in organic matter to the ammonium and nitrate forms (called mineral nitrogen). Since this conversion process depends on the highly variable factors of soil temperature and moisture, it is very difficult to predict. Nitrate nitrogen is the form most commonly used by plants, though some can use ammonium nitrogen for part or all of their requirements. Nitrate is also the most easily leached of all nutrients, since the soil has almost no capacity to hold it. Measurements of mineral nitrogen are most meaningful during the growing season, but not during early spring or late fall sampling periods." from http://umaine.edu/gardening/master-gardeners/manual/soils/interpretting-soil-tests/

"Due to the high mobility of nitrate and seasonal fluctuations in nitrogen levels, nitrogen tests may not give an accurate assessment of the nitrogen availability in your soil. Dr. Keeney suggests testing the amount of organic matter in your soil instead. "Organic matter is about 50 percent carbon and 5 percent nitrogen on average. So it is easy to use your organic-matter figure to estimate total nitrogen," says Dr. Keeney. It's good to have soil that's composed of at least 5 percent organic matter. Most soil testing labs will perform an organic-matter test upon request. If a test shows that your soil has low organic matter content, begin adding organic matter and supplement your plant's nutrient needs with an organic fertilizer" from http://www.organicgardening.com/learn-and-grow/soil-nitrogen-content

[engineer]

OK - I wasn't great at maths, even when I needed to be (which was a long time ago), but I think this is correct:

Formula (per 100g of made-up fertiliser): grams of each ingredient =  required %/actual % X 100

For the 6:10:10 potato fertiliser this equates to 29/56/20 grams of the NPK ingredients respectively (total 105 grams)

For the 6:8:15 onion fertiliser it equates to 29/44/30 (total 103 grams)

NPK analysis is based on the proportions by weight, so given that the ingredients are likely to be of different densities they would need to be weighed rather than measured by volume, although it's not an exact science and would probably make no difference in practice - how much you apply, your soil, and the weather will all have a bearing on how it's actually used by your plants.

Thanks JayG, that is just what I was looking for 


edit to fix quote

[Steve.B]

OK - I wasn't great at maths, even when I needed to be (which was a long time ago), but I think this is correct:

Formula (per 100g of made-up fertiliser): grams of each ingredient =  required %/actual % X 100

For the 6:10:10 potato fertiliser this equates to 29/56/20 grams of the NPK ingredients respectively (total 105 grams)

For the 6:8:15 onion fertiliser it equates to 29/44/30 (total 103 grams)

NPK analysis is based on the proportions by weight, so given that the ingredients are likely to be of different densities they would need to be weighed rather than measured by volume, although it's not an exact science and would probably make no difference in practice - how much you apply, your soil, and the weather will all have a bearing on how it's actually used by your plants.

Thanks, great stuff.

[Steve.B]

A popular organic alternative is chicken manure pellets.

The foxes dig around when we use chicken manure.

[JayG]

Foxes (urban variety in my case) have been repeatedly digging up even the bare soil this winter - luckily they've left the remaining parsnips and leeks alone so far.

I realised they found BFB irresistible a few years ago, dried chicken poo was "OK" if you could put up with a few exploratory digs before they got the message, but last year they were even digging up the areas I'd used Growmore on (it's supposed to be an inorganic product but my latest tub had more than a whiff of "poo" about it - something wrong there.  )

[JimB]

.

Epsom salts (mag) is a trace element,  usually only needed on tomatoes under glass, at one teaspoonful to two galls of water, once per growing season!

Outside it is not needed as most commercial fertilizers have it added!

Also I doubt very much there is no nitrogen in anyone's soil at the moment, it may be the most volatile but that is the one that makes everything grow and every plant that should be growing is springing into life in my garden!