Thursday 8 August 2013

Garden myths discussed 7: Plants need there own special fertilizer.

Not really a myth, and this notion is not generally acted on by experienced technically minded gardeners. It is just a gentle deception ‘sold’ to the gullible public that helps to keep the garden centre tills ringing. 
Over the years I have noted on the gardening shelves of aunts and uncles - when I have been pressed into some gardening chore - lots of tiny packets just sitting there, never used, of all sorts of special concoctions for every plant they grow.
There is not usually anything wrong with these mixtures and they are certain to be much better than bonemeal. Rose fertilizer for example has a suitable balanced analysis that will be suitable for almost all of your plants.

My balanced granular fertilizer. Granules facilitate ease of spreading. They are NOT slow release

John Innes composts

Before William Lawrence and John Newell developed John Innes compost at the John Innes Research Institute in the thirties it was generally believed that every plant needed it’s own special compost together with its own special nutrients. Recipes were closely guarded secrets of head gardeners and often went with them to the grave. Lawrence’s great contribution was that he showed that a simple series of composts could fulfill, almost, but not quite all, plant requirements. The four  composts he developed were named J.I.Seed and J.I.Potting Compost, One,Two and Three. The only differences between JIP1, 2 and 3, was the strength of the fertilizer and lime, which increased three-fold between JIP1 and JIP3. It started to be whispered that these new fangled composts were much better than any of the old ones.

Unfortunately John Innes composts are not patented and any old rubbish can be sold as John Innes today. Modern mixes use more up-to-date fertilizer ingredients rather than the original formulae and there is nothing wrong with that. Plants that make vigorous growth and/or have a high nitrogen requirement are planted in the richer mixes. Delicate young plants must always be started in weak compost. J.I.Seed is now largely superseded by loam-less seed compost but J.I. Potting, if from a reputable supplier and certified by the John Innes Manufacturers Association  gives excellent results. Alternatively you can mix it from your own from basic ingredients.

The point I am making with my long winded digression is that when it comes to giving nutrients to plants, simplicity is best.

Why I use just one general fertilizer and reject ‘special mixes’
  • If  general fertilizer has a fairly even balance and contains all the plant nutrients including trace elements, the plant will take from the soil what it needs.
  • It is much cheaper to buy a large bag of a general fertilizer than buying lots of expensive little bags.
  • It is easier and less time consuming.
  • There is less wasted fertilizer when all those separate bags deteriorate on the shelf.
  • There is no guarantee that special fertilizers are better for your plants. Their analysis might be due to popular fashion and is just as likely to be formulated by an adman or bean counter than a proper soil scientist.
  • How do they know what nutrients my plants need? Does it not vary with the nature of the soil, season and weather conditions?

What about nitrogen?
In the wild plants greedily seek out nitrate because in natural soils it is usually in short supply. When fertilizer is used there is a danger that certain plants will absorb too much nitrogen and make unbalanced ‘soft’ growth susceptible to pest and disease. I avoid this problem because my general fertilizer has a fairly even nutrient balance. Where plants like brassicas and grass need higher levels of  nitrogen, I merely apply a greater amount of my balanced fertiliser. It is much cheaper that way and any unused potash and phosphate remains in the soil for a future crop.
A much admired former horticultural colleague and very keen vegetable grower, in addition to his balanced fertilizer had a high-nitrogen fertilizer in his arsenal, the dreaded 20:10:10. Much used by farmers, it is horticulturally lethal in inexperienced hands!

Do you need to use any special fertilizers?
Slow release fertilizers may be appropriate if you are making up composts or preparing soil for tubs.
Certain nutrients can be ‘locked up’ in the soil. For example iron is frequently in short supply for acid loving plants grown in an alkaline soil. Some gardeners might need to supply trace elements in ‘chelated form’ (usually marketed as sequestrene).
Regular readers will know I am very partial to iron sulphate for my lawn!
The only liquid feed you need is a ‘tomato’ liquid feed. It is suitable for any of your plants.

What about lawn fertilizers?
I actually use my general fertilizer on the lawn! One hardly ever sees a lawn fertilizer these days that does not have added weedkiller or moss killer. Most lawn fertilizers are high in nitrogen which gives rapid growth of vulgar dark green grass. Personally I do not want to cause rapid grass growth. By all means use branded lawn fertilizers, but do not include me! I do not see many economies of scale when I see their price in the garden centre!

But don’t commercial growers use special fertilizers?
Many growers are specialists and grow very large quantities of a limited range of crops. They frequently have intimate knowledge and have technical advice as to their own plant’s precise and varying nutrient requirements. They have economies of scale when they buy. They are not paying premium prices for small bags! It makes sense for them to purchase exactly what their plants need.

I currently use this general fertilizer which I buy from a local horticultural supplier. A 25kg bag lasts me about two years.

I discuss my own take on compost in ‘Breaking the rules’


  1. Roger, I'm with you on this. I use "Growmore", which seems to do the job well, and is easy to use. Probably not much different to the one you use. I don't buy a 25kg bag though! One kilogram usually lasts me a year in my small garden.

    1. You make me feel very extravagant Mark! As I have mentioned before I do not use any fertilizer at all in my ‘other’ gardens. Perhaps my bag lasts a little longer than I say!
      I think you use manure Mark and of course with regular use of manure you can achieve superb results with no fertilizer at all. As mentioned I do use mine on the lawn and although I give it a very low dose I do have a lot of grass! I also use it on all my fruit and a limited number of ornamentals such as delphiniums in my own acre garden. And the asparagus!
      I do make up quite a lot of compost for my plant sales or producing plants for my other gardens and we have loads of tubs and planters and conservatory plants where I use my fertilizer. As also mentioned in my posts I do not liquid feed and top dress with my fertilizer instead. Oh yes I do sometimes give some to friends! And of course my tomatoes are very hungry…
      Thanks for your helpful comment Mark. You have got me wondering where all mine goes!

  2. I am always amazed by how many different 'specialist' fertilizers there are!

    Another thing that irritates me about garden centres is how the sell tender plants too early so when a purchaser plants them they die and the said purchaser thinks its their fault and just buys more later. They also bring on plants under glass so they flower and look attractive to customers before they should. We had a local nursery, which is sadly no more, that refused to stock bedding plants before it was time to put them out.

    1. I agree Sue. I think one of the reasons we write our blogs is to help educate less experienced gardeners. Television and horticultural press rarely go beyond recycling the elementary and never tackle anything detrimental to the trade.

  3. Useful information for me Roger as I'm not an experienced enough gardener to know that "one size fits all" for fertilizer. I'll make the change immediately especially as I have two citrus and I can use it for those too.

    1. Thats good to hear Craig. You have probably read my old post NPK fertiliser via the link in this post and seen my calomondin orange top dressed with my Yara Mila fertiliser. I am particularly happy to do this as my fertilizer does contain trace elements as well as all the major nutrients Although I would confirm Mark Willis's advice above - that growmore is the balanced fertilizer he uses, and I frequently recommend and often have used it myself - It just contains 7:7:7 NPK and no trace elements. I would venture that his growmore would be very good for your citrus but just have a small doubt that the plant might miss the trace element

  4. Interesting to read how other people use fertilizers. I do very much the same and mainly use NPK 12-10-18, good for everything. Furthermore in autumn the roses get cow manure and I use my compost from the heap. I have one exception: the Delphiniums, they love bone meal twice a year, because we have peat soil.

    1. I should have guessed Janneke, I know you are in Holland but on peat soil....
      I have happy memories visiting the town of nurserymen Aalsmeer with our horticultural students. I remember a grower demonstrating by pushing a ten foot rod deep in the peat soil.
      Unlike our mineral soils which hangs on to phosphate as if it were a limpet, the same nutrient does leach from peat and perhaps therefore your love of bonemeal.
      My own prejudices against bonemeal are too great but I have been known to be wrong.(Brenda would say most of the time)

  5. Oooh aaargh! As a professional plant nutritionist and supplier of professional fertiliser products I have to disagree with much of what I read above (plenty to agree with too). I wish I had more time to go through point by point, but not for now, although any specific quesions, I would attempt to answer. I won't profess to know it all, but have studied and worked in plant nutrition and soil science for some years now.

    Growmore a generic name for a granular 7-7-7 fertiliser is a useful general purpose fertiliser, however I estimate that more than 90% of the time it is used more than 85% of the phosphorus will be locked up in the soil and probably never utilised by the plants. So we'd all be better using a 7-1-7 and saving our cash and looking after the environment. High levels of phosphate in the soil can cause other problems.

    Your 12-11-18 with secondary and trace elements is as a general fertiliser a better formulation than 7-7-7, but still too high in P for most applications.

    What's wrong with bonemeal? 3-18-0 or thereabouts depending on source, it makes an ideal slow release, 'organic' fertiliser for use at planting or an annual dressing of bulbs. This source of P is likely to release and be utilised by plants far more efficiently than chemical sources of P found in your 12-11-18 or growmore.

    Specialist & general fertilisers are available from Angus Horticulture Ltd, if I may mention them - not all they offer is on their website, but they always offer high quality products of integrity and excellent customer service.

    1. Good to have some debate SAP! I agree about the dangers that phosphate can easily get locked up and I would also argue that few British soils require any extra phosphate. I remember visiting Headingly cricket pitch in the early seventies with our horticultural students and remember the then new head groundsman decrying bonemeal used by his predecessor and saying that the pitch needed no more phosphate until the next century. That of course occurred thirteen years ago! One of the reasons I recommend growmore and use myself Yara Mila is that both are readily available and relatively cheap. I imagine if I were to seek out 7:1;7 it would not be cheaper but would cost an arm and a leg.
      As to using bonemeal on bulbs! Why ever give them extra phosphate? I bet there are not any dutch bulb producers and East Anglian daffodil producers who ever put bonemeal on their bulbfields!
      I was also under the impression that bonemeal had been shown to lock up phosphate so tightly that even organic gardeners had given up on it. My botanist friend Mike was recently describing bonemeal as a very undesirable soil phosphate pollutant.
      I don’t mind you popping in your ad for Angus Horticulture. I know a scotsman called Angus very well and he was in the fertilizer trade. I don’t think he thought very highly of bonemeal either.

    2. Forgot to say SAP that I do appreciate discussion about my posts. Thanks

  6. Hi Roger! Great discussion. I got this reference about the organic fertilizers. Here's the link if you want to check it as well:

    I'm just curious about the mineral-based organic fertilizers in the article. It says it's from naturally occurring deposits. What's your claim for this? Have you written a post related to this?

    1. No I have not written about natural 'organic' deposits Melissa (those which are clearly inorganic like sulphate of potash) but I will! I personally think it a bit of a nonsense to differentiate them from other inorganic materials but it is great marketing. North Yorkshire has huge deposits of these inorganic organics (yuk) as natural potash compounds And I am even toying with buying a few shares in Sirius mining that own vast deposits. There is an environmental issue over extraction on North Yorks Moors- its so difficult with ones ethics conflicting these days.
      As to the mention of compost in the article I do not regard it as a fertiliser, but very much more as a bulky organic soil improver that does of course contain valuable nutrients.


Note: only a member of this blog may post a comment.

Related Posts Plugin for WordPress, Blogger...