Friday, 18 July 2014

Garden myths discussed. Does bonemeal have any horticultural value?



Every time I used to read a gardening article written for amateurs it recommended bonemeal to encourage new roots and fertilise the plants. Whatever the plant, be it grass, bulbs, vegetables, fruit, shrubs, trees and herbaceous perennials it was a panacea and almost mandatory to use it when planting and sowing. 

Whenever I looked at any professional fertiliser recommendations for each one of these plants there was never a mention. Be it nurserymen in Boskoop, farmers at home, fruit growers in Kent, bulb growers in Spalding or vegetable growers in Lincolnshire they all used  fertilisers, usually compound -  but bonemeal.....? Not a word!

Why was this so? It's not much better now. I have agonised over this conundrum for many years and I have concluded it is so widely recommended because it does very little harm. Gardeners (wrongly) feel it is their duty to put a little something into the planting hole to give the plants a good start. Most gardening journalists apart from believing the myth themselves - it must be right because it is repeated ad nauseam - do not want to give any cause to the  gardener to damage or kill his plants. There are people who imagine that if a slack-handful of fertiliser is recommended, either they might have very big hands or are of the mind that if one is good, ten is better. Proper fertilisers contain highly soluble nutrients and too much will damage or even kill plants.

I often recommend Growmore to amateurs, it is a good compromise between too much and nothing (bonemeal). Growmore contains the major nutrients, 7% nitrogen, 7% phosphate and 7% potassium. Better and more concentrated fertilisers are available and these I have recommended in previous posts but clearly the stronger they are the more room for abuse.

A general fertiliser far superior to bonemeal and excellent for amateurs. I remember when it was called NATIONAL  growmore but am too young(!) to have dug-for-victory
Just one final salvo before I try to analyse this myth. Bonemeal smells a little acrid and highly organic. It must be doing good! When I say bonemeal is harmless I believe this to be true. The last time I was in Eire (fifteen years ago), bonemeal was banned - something to do with anthrax as far as I know. Thinking about flinging the powder of crushed denatured bones around it amazes me that in the reaction to the very real  BSE scare they did not ban bonemeal in the UK. There is a complication here, if you check things out on the net, bonemeal can be used in animal feeds where their are different regulations.

Superior to bonemeal, perhaps equivalent to growmore for organic gardeners unless in some formulations its enhanced potash is from an inorganic source. Perhaps you are troubled with taking fish from the sea?
So what's wrong with bonemeal?
Other than;
it contains only phosphate, a negligible amount of nitrogen and normally unnecessary calcium; 
that the phosphate only becomes available in minute quantities even over several years; 
that most garden soils already contain more than enough phosphate; 
that there is little evidence that roots require phosphate more than any other nutrient;
that it is immobile and remains where you put it - and even if roots really do grow towards phosphate, because it remains in the planting hole it will NOT encourage roots to grow out into the soil; 
because extra phosphate might inhibit mycorrhiza and even render other nutrients insoluble; 
it is a very expensive way to buy phosphate when a cheaper compound fertiliser is better;
then I have no objection to it at all.

If you learnt on your mother's knee (she will be well over a hundred now) that bonemeal is an excellent fertiliser events have overtaken you. Modern methods extract all the goodness from bones and you buy the debris.
Bonemeal needs to be mineralised - that is worked on by bacteria - before any soluble phosphate is available at all. If the pH is more than seven it will be immediately locked away and even when the soil is acid, one study showed the nutrients took more than ten years to be released. One enterprising vendor took a positive view and advertised ten years supply in one go! 
Mike Ashford my botanist friend described adding bonemeal to the soil as a form of pollution. I know no professional colleague who ever uses it. I would not put it on my garden if you gave it me for free! You have perhaps by now have decided I might be a little biased. 

About the nutrient phosphate
I hope I have not given the impression that I have  something against phosphate. It is a major nutrient required for the development and function of every plant cell. It is contained in almost all compound fertilisers but it is not usually necessary to provide it separately as a single nutrient fertiliser. It is particularly important for seedlings and young plants. It is not for nothing that superphosphate is the sole fertiliser ingredient of John Innes seed compost - not used now and superseded by loam-less seed composts, it gave fabulous service to amateurs and professionals for more than fifty years. 
Although most phosphate fertilisers (other than bonemeal) are more or less soluble when they are used on the soil, in a matter of weeks they become chemically 'locked up' and much less available to plants. An equilibrium exists between ‘locked up’ phosphate and small amounts dissolved in the soil water. The available nutrient is effected by acidity and alkalinity, is optimally available between pH 6 and 7 and where temperatures are sufficiently high. Phosphate in the soil is like capital in a bank that remains in place (dream on), and small withdrawals are made.
The consequence of this is that in the soil, phosphate, in effect, acts as it's own slow release fertiliser. Perhaps only 20% of phosphate added as fertiliser, is used by the current crop. The remainder remains as capital in the soil 'bank' for future years. Most UK soils have more than enough phosphate and need no more for several years!
Because phosphate becomes locked up in the soil, it is not very mobile and tends to stay where you put it. That's one in the eye for none diggers like me who top-dress only and do not work fertiliser in. My numerous worms relocate the absorptive soil and the roots come to the surface without being chopped away in my undisturbed soil.
Another consequence of the low mobility of phosphate is that not only does it not readily wash into the soil, it does not leach out. Unfortunately this does not always prevent water pollution if soil particles are eroded by wind or water, or phosphate from decaying organic matter left on hard surfaces runs straight to the drains.

In early May, Peter William's commented that he had never before seen such intense purple-leaf symptoms of phosphate deficiency on my tomatoes! (sorry no picture). After being planted in my greenhouse at the end of April there had been a spell of rather cold weather and the air temperatures in my greenhouse were almost zero centigrade. Warm weather returned and my soil supply of phosphate became available and now in late May my tomatoes are fully recovered.

In mid July we are within a few days of picking. The initial phosphate deficiency has done little harm
A little known fact in the UK, is that many Australian soils are naturally deficient in phosphate and some plants from that continent have evolved with a low phosphate requirement. In a very limited number of cases in UK soils, such plants have suffered from phosphate toxicity.

Have I been fair to bonemeal?
Probably not. It was a cheap jibe about it locking up other nutrients. That is a property of phosphate and not a specific fertiliser. Indeed the fertiliser superphosphate is sometimes used to lock up heavy metals that are potentially toxic.
As to it's effects on root growth I was perhaps over-anxious to counter the usual baby talk that phosphate is for roots when I fully admit that phosphate is good for the development of young plants (pity that bonemeal provides so very little).
Although the release-rate of phosphate from bonemeal is hardly perceptible that is not little different to the effect of normal phosphate when it is locked up in the soil.
It is generally recognised that fertilisers reduce mycorrhizal associations forming. The release rate of phosphate from bonemeal is hardly enough to make any difference!

And finally a story about bonemeal
No, not the one about West Hartlepool Parks Department making their own version of John Innes compost with bonemeal when I was an apprentice.
No, not the one about nearly coming to blows in a pub.
No, not the one about plenty of bonemeal in my cemetery gardens.

In the early seventies we took the students to see the turf at Headingly cricket and rugby stadium. The new groundsman was scathing about his predecessor's use of bonemeal. He had had the soil analysed and rhetorically declared that there was enough phosphate stored in the soil to last to the millennium. Wonder what happened in 2001?

With trace elements superior to growmore


My current professional fertiliser. Brother-in-law Dave recently bought 25kg from my sundries supplier for £22 to share with fellow allotmenteers. As a hard prill formulation it stores very well.

My previous  fertiliser posts



14 comments:

  1. For no particular reason (other than that I emulated my Dad) I have always used pelleted Growmore - and had good results from it. I have also been known to buy Vitax Q4 occasionally, but I admit that I am ignorant of the science involved!

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    1. Yes growmore is a really good fertiliser and I take it as read that it is best when granulated as this eases and speeds up spreading, especially when you top dress by scattering as I do
      Vitax has the qualities of a base dressing and can be used as the base fertiliser in making up compost - although I prefer the modern coated controlled release fertilisers for this purpose.

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  2. Every time I watched a gardening programme in English, they always recommended blood and bone meal. This fertilizer was so much touted that I wanted to have it. Unfortunately, I couldn't find it in Poland.

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    1. I am sure if you get a balanced general fertiliser of similar analysis to growmore you are not being deprived Dewy!
      Great that someone reads me in Poland!

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  3. I agree with you entirely, as my post on Gardenmyths.com says:

    http://www.gardenmyths.com/top-10-gardening-products-not-to-buy-10/

    In addition to your comments, I believe it also attracts rodents like squires, a big problem across the pond. Most soils in North America also have lots of phosphate. A number of locations have banned phosphate from lawn fertilizers. In Ontario, manufacturers have started removing it voluntarily.

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    1. Thanks for your endorsement Robert.
      Gosh a blog on myths, I rushed to your site and joined today!
      Your comment about manufacturers reducing the phosphate.is very interesting. I think I should do the same with the one general fertiliser I use generally but I suspect that as an unusual analysis over here it will be more expensive. Does anyone know a good one?

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  4. A very interesting post Roger. I did not know anything about bonemeal.
    It is interesting that whatever fertilizer is being recommended or not, it seems to me that what in fact matters is to have a soil rich in humus and alive with micro-organisms that will help plants get to the nutrients (whether these nutrients are present or not in large quantities). In other words, feeding the soil rather than the plants.

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    1. I agree Alain. I hope you agree that this is a regular theme on this blog - it all depends on wise management of the soil- even if this is by leaving it to nature!

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  5. Oh dear so we are wasting our time using fish, blood and bone? I shall now go away and sulk!

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    1. I would not want you to sulk Sue.
      If you read the caption under the picture of meat, fish and bone I said it was as good as growmore - and I regarded that as a compliment! albeit the little dig at the thought of using fishmeal as a fertiliser!
      I did not show a picture of any branded bonemeal as my comments would be defamatory!

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  6. At last the long awaited bonemeal post! I remember reading a book on shade loving plants with individual descriptions, under the heading Maintenance in every case there was the advice to "scatter a little bonemeal around the plant in the spring" and I suppose that is how it has always been as you stated. I think the myth grew up around the fact that bonemeal was likened to a plant's comfort food it was an organic "slow release" fertilizer unlike this chemical muck these farming chaps were using, I mean who wants to pollute and burn their precious plants with these modern chemicals. The irony is, of course, that it remained popular because it was somehow cosy and generally safe and yes, innocuous. I am currently using a 15:15:15 but you have made me think again about the phosphate content. I have included a link to an interesting article and site I have found.
    http://puyallup.wsu.edu/~linda%20chalker-scott/Horticultural%20Myths_files/Myths/Bonemeal.pdf

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  7. After our previous banter it was with some intrepidation that I opened your e-mail! I should not have feared and there was your usual wise words. I really do appreciate your contributions to my posts. Together with Sue and Alain.
    Thanks for the link, sorry it does not come through live but google will quickly find it for interested readers. Coincidentally I had already found it when checking out whether there were others who agreed with me.

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  8. Very good and balanced post, Roger. I formally used bonemeal as it was recommended by Cornell for natural additives. I guess when you think of animals dying and decomposing where all goes back to the Earth, it kinda makes sense. I stopped spending the money on it though.

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  9. You are quite right about dead animals Donna. We planted a beautiful yellow magnolia on the grave of our dear cat - and the tree has grown magnificently. It used to be a country tradition to bury a dead farm animal under a new tree. There will be every plant nutrient available.

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