Wednesday 23 November 2016

Garden myths

What are they?
Peter described them as truths, half truths, damned lies and magic.
They are certainly slippery creatures and refuse to die.

Take the old hospital practice of removing flowers from a ward at night; silly nonsense based on the idea that although plants make oxygen in the day they use it up at night when they respire – the image is worse these days, they make carbon dioxide! Of course the amounts are small. A single human breath will emit more carbon dioxide than a plant will make all night.

Or perhaps removing flowers was an old fashioned practice, the reasons born in antiquity seeking a new explanation! Garden myths and even garden truths frequently have their measure of pseudo-science.
If I were in an argumentative frame I might even find reasons to justify removing hospital flowers.
Perhaps some flowers will shed pollen or even smell. Allergies seem to be very common.

I fear I might not be doing you a service today when I attempt to destroy your illusions.
Take a real horticultural example. Many gardeners believe that evening or night is the only time to water plants. There are reasons - some of them wrong and others insignificant. It is unfortunate however that the belief extends to not watering at all in the day. I shudder at the thought of a plant dying of drought in the morning and the gardener waiting to water later.

This koheria is wilting of drought - I have checked it is not wilting by water logging - I will water it immediately

I shall continue to benefit from high water pressure from the tap on a Summer morning when it’s a mere piddle at night when everyone else is watering.
Of course if watering in the evening is a pleasant and relaxing end to the day do carry on!

I sometimes fear that when I write about myths that no one has ever heard of I do my bit in keeping incorrect notions alive!
It used to be believed that soil cultivation was needed for numerous reasons and that this was essential to grow plants. It would seem that although there are sometimes good reasons to stir the soil that if you can control the weeds – usually with herbicides in the case of commercial production – there is no need to cultivate at all. In the old days it used to be believed that cultivation was needed and for example hoeing conserved water.  Agricultural research showed this to be wrong.

Where do myths come from?
Their provenance is legend. Here are a few examples
  • They arise from trivial convenience and with time are elevated to need. It is convenient to add egg shells to compost but they are no value at all as a source of calcium. Un-decomposed egg shells are found in Archeological digs!…..scientist Peter Williams, (henceforth PW)) says you would need very strong acid to dissolve egg shells.
  • They arise from common sense. Common sense apart from not being very common is frequently wrong. Painting pruning wounds with sealants satisfies all our instincts and yet has repeatedly been shown to be harmful. This myth persists for too further classical reasons – it is often stated by authoritative figures and we tend to look for ‘special cases’ - note apple canker is NOT a special case.
  • Seeking explanations of actual problems – often by the means of misunderstood science. Leaf scorch is a genuine phenomenon although much less likely than people imagine. It is widely believed that water makes water droplets on leaves concentrate sunshine. Utterly wrong.
  • More mis-appliance of science. Mycorrhizal fungi can be hugely beneficial to plants. Levels of bacteria can influence or indicate soil conditions of life or death. It is almost invariably useless to add such organisms to the soil from a bottle!
  • Myths embedded in belief systems. Organic fertilisers are not generically better than inorganic ones. In my view they are frequently grossly inferior. This does not mean that any specific fertiliser cannot be better for individual tasks. There is a belief that fertilisers are bad for soil structure. Although fertilisers’ growth stimulation can hide other bad practices, when properly used they can bring huge improvements to soil fertility.
My inorganic Yaramila fertiliser provides all the necessary plant nutrients and in no way damages soil structure

  • Whims of famous people. I have written about the nonsense that rhododendrons exude natural plant toxins. It arose because the idea sounded plausible and it was repeated at a Conference.
  • Many garden gurus are not practical gardeners and many know no science! They often carry godlike authority. One once said that tomato/potato blight spores cannot properly penetrate into a greenhouse and that was the reason why greenhouse tomatoes are less susceptible to blight than those grown outside! I won’t insult my readers by explaining why his explanation is wrong. On another occasion a ‘personality‘ said that a banana was a herb. True in a garbled way!…. whoops  it was the same gg
  • PW who is an avid watcher of TV gardening describes one programme as  ‘a school of myths’
  • Editors! They like a good story! They don’t like it however when one that they have used repeatedly is shown to be wrong. Apparently recommendations to grow nettles in your garden to encourage certain butterflies is misguided. Insects hosted by nettles prefer real strong stands in the wild. Only very rarely are the said butterflies seen on nettles in a garden. When one ecologist conntributer reported this embarrassment to an erudite journal it was edited out. 
  • Claims that will make money! There are a lot of gullible gardeners around.  There are plenty of snake oil vendors too. For many products scientific evidence of efficacy is zero and any research is inconvenient. The gullible actually pay good money to put powdered rock on their garden.
*  Wrong conclusions drawn from sound gardening practice! I frequently promote all the advantages of recycling organic matter. There is a whole cult of biodynamics. This claims that nutrients can be ‘mined’ by deep rooted plants. It is true that certain elements can be brought up from considerable depths. Indeed trees have been shown to indicate mineral deposits below. In your own garden levels of nutrients are minimal below the topsoil. Your most fertile organic debris received its nutrients from roots near the soil surface. By all means compost your comfrey or hoe and recycle the tops off your marestail. They are all good organic matter but don’t bother your head with thoughts about  dynamic accumulation…. whoops I noticed on my old post about green manuring I told this porky myself.
  • Recycled old technologies. The old and still invaluable ‘hormone type’ lawn weedkillers such as MCPA and 24D were sometimes thought to be most efficiently translocated to the root when a weed was about to die down in Autumn. I frequently see the same principle claimed for the translocation of glyphosate. In my own experience the best time to kill a difficult weed with glyphosate is when it is large and actively growing. Even this maxim is not consistent with gardeners being told in every gardening article they care to read about lawns, that they must use their lawn weedkillers before the end of September. I prefer to weed-kill my own lawn in October or November
  • I heard a good one on the local radio gardening ‘phone in’ yesterday. The pundit earnestly explained that roots in wet soil in pots in Winter are physically damaged when frozen water expands. It is common knowledge that plant roots in pots are frequently more vulnerable to freezing than those still in the ground…but this is not the reason
Reading about Myths
I titled my early posts about myths ‘Garden myths debunked’ This was rather pretentious but easy to do for  myths that were so obviously wrong. I soon changed to a title that more reflected myths’ occasional part truths. You can find  links in my theme column. Unfortunately Google only brings up the latest ones from any long list – hence my sub-divisions of their titles.
Most of the myths I have written about such as those that say you should not apply glyphosate or fertiliser in Winter  are separately titled!

I must thank  Canadian blogger Robert Pavlis for some of the myths I mention today. Over the pond the American market would seem to be saturated with false claims. (In the USA they have shown recently their susceptibility to lying). Robert is tenacious in tracking garden myths down and explaining why many are nonsensical. Not only does he do his own practical demonstrations, his articles are widely researched, plainly explained and sources are precisely linked.
Apart from tackling trivial misunderstandings he is prepared to take on major issues. He recently took to task a famous Ted Talk. Widely circulated the talk makes highly inflated claims for the benefits of plants in buildings.
The talks’ flagship propaganda is a famous building stuffed with plants. The benefits claimed for the plants are more likely the result of the building’s specially installed air purification system!

Although I have suggested elsewhere that organic gardening is itself based on the nonsense that things inorganic are inferior to those ‘organic’ I am a great admirer of organic gardener Charles Dowding. I reviewed his book about myths. He challenges much of traditional garden lore and is well worth reading.

The Garden Professors do not seem to publish any more. If you locate their old site you will find very interesting reading about misguided and over rated gardening practices.
Unfortunately their prime mover was sacked from an American university extension department because she spent her time informing amateurs rather than churning out  money-raising research.
Linda Chalker is still very active on Facebook and the site is a very good source of information. They have a policy that technical data quoted by followers is based on ‘peer reviewed science'. The idea is to keep out the nonsense.
I do have my own reservations. Wrongly interpreted science – in the press a very common occurrence – leads to the greatest myths of all.

Links to relevant sites
Garden Profs. Go to this link and scroll town the left column – beyond the dated entries - to find a trove of information. Try the title ‘skeptics’

I review Charles Dowding

Poor Poppy (RIP) devoured the book

Robert Pavlis  tauntsTed

Will this purify the air?
Robert knows a lot about ponds

I am taken in by bio-dynamics

I read in last week’s  New Scientist a serious article about the problem of city air pollution. The article concludes with six bullet points of suitable measures that might be taken. The last one is to get a house plant!
I ask you!


  1. If plants suffocated you in the night our bedroom full of plants would be a murder scene.

    We've always watered the allotment when we visit whatever time of day. I

    So I guess that you are a non-believer when it comes to the benefits of houseplants?

    One of our ex radio gardening guru suggested that aminopyalid contamination could be washed out as he couldn't comprehend how it worked. People revered him giving him gardening god status and his programme kept winning awards.

    1. I am a huge believer in houseplants to make you feel good and happy and give you loads of pleasure by growing plants!
      As Robert Pavlis explains in the link to the Ted Talk comment it needs a huge number of plants to bring any environmental benefits indoors.
      You might get problems such as damp walls if you do have a huge number. Harry always used to complain about our conservatory plants contributing to damp walls.

  2. In our house we have a general term for this kind of nonsense, we call it 'hairdresser science'. This is because hair myths are very common and often totally ridiculous. From the silly ones like 'hair grows faster if you cut it' to the mumbo jumbo that the product manufacturer's create. A well known shampoo claimed to contain 'satin proteins'. Really??? As satin is a type of weave, and not a raw material, there is no such thing.
    I hope there aren't any hairdressers reading this, and if there are I hope they have a sense of humour :-)

    1. I can think of several other professions that make up their own science but I will keep my head down Sarah
      As Brenda has abandoned her basin and stopped cutting my hair and it is now cut by her lovely hairdresser I will say nothing about them too.
      She is amazed that my hair is in lovely condition - the little I have got -and is NEVER washed

  3. Thanks for the kind words. I have been collecting myths for years and have hundreds I have not written about yet.

    I am fairly sure Linda still has her old job, but they threatened action against her. Not sure why they no longer post to the blog, but it was not working correctly for quite some time.

    So much to learn and so little time.

  4. Glad that Linda kept her job!
    I enjoyed your latest post on mulches - can't remember the myth bit at the moment because as you showed they can be very valuable. I feel inspired to do a post on mulches myself

  5. I received this reply when asking permission to use a renowned ecologist's comments about my next to be published post on Hymalayan balsam.

    Dear Peter
    Yes, he's welcome to use it if he wishes (can't remember what I said but I am sure it was very profound). I don't usually follow blogs so I had a look at his latest one - about garden myths. I agreed with him about the gm - especially the one about not bothering to add mycorrhizal fungi - but not entirely with his preamble about hospital flowers: the reason they are now banned is because as they age they are a source of fungal spores and immunosuppressed patients could be at real risk. Of course, most patients in hospitals are not immunosuppressed, so flowers would probably be quite ok on general wards.

    best wishes



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