Wednesday 1 January 2014

Remembering myths

Garden myths listed

It is traditional at this time to look back over the previous year. Today I would like to review  the nine myths in my series through the life of this Blog. It gives me an opportunity to blatantly advertise my wares and in addition clarify a few points that were previously blurred. 

You might have noticed that many of my myths relate to the soil. No surprise there then, it is one of my former lecture topics. I do find in the popular gardening press that very little is written about the basic elements of soil management and when it is, it is frequently wrong. When I struggle to read some of my older posts it makes me realize why so little is written!

Gardening is a minefield of mythical magic. Some so-called ‘facts’ are totally wrong. Many more are half truths based on unverified personal experience, outdated techniques, wrong explanations of verified facts, simple recipes that have more exceptions  than actual cases and at other times just pure opinion and much imagination.

I started my series with ‘debunk’ in the title. I soon realised that not only did this sound rather arrogant it did not cover most cases of factual dispute. I now prefer to attempt to ‘discuss’. Early on I failed to put the topic of the myth in the title. It makes it easier to use my search box now that I do. Except that for a couple of months now my search box has failed to work at all!  What a headline it makes, Google fails to find! 
Fear not I have provided links to each of my myths. I have recently been reminded that new readers do not always appreciate that to go to an old post you just click on the coloured highlight!
nb the very small search box at the very top of the blog finds and takes you to old posts  - best if the search term is either a single word or a an exact phrase. The large box at the bottom does not work at all.
Another way to find old articles in blogs is to go to any search engine and insert the blog title followed by the subject. ‘Roger Brook myth’ will find all my relevant posts.
Whilst I am going on about blogging, I would like to point out that blog comments are much appreciated in ‘old posts’. Blog writers receive an e-mail for each new comment and will almost always respond. When I started blogging I thought stuff in the archive was like old magazines and never read. Nothing is further from the truth and as search engines find them, old posts take on a life of their own!

The blogs

My first myth about water on leaves acting as a lens and sunshine scorching leaves is fairly uncontroversial and clearly untrue. Even with this myth, leaf scorch is a common phenomenon and sunshine can be involved when it causes desiccation in conditions of severe dehydration in drought.

The folly of using tree paint was also straightforward. I remember a former employer who had wounds on the trees in his arboretum expensively painted in a horrible blue. Above a cut on a beech tree I remember the biggest bracket fungus I have ever seen.

The common confusion between a (harmful) wireworm and a (beneficial) orange/yellow centipede was merely a matter of report.

The myth that it is better to water in the evening is common gardening lore. It seems so obvious to give plants a drink at night when surfaces will remain wet. Counterintuitively  water on a wet surface does not sink in at night in some magical way. If you give so little water that increased evaporative loss in the day is significant you are not giving enough water.

I had a hard time with my assertion that ground cover plants do not conserve water. It seems so obvious that they do conserve water when leaves shade the ground! The crucial point fundamental to all irrigation practice is that the very same leaves transpire oodles of water that thirsty roots have sought out deep in the soil. Many gardeners overwater small plants, especially in containers, when they fail to recognise this simple fact.
Water conservation is in practice more complicated than this. Plants have wonderful adaptations to conserve water when subjected to drought. Conversely, and less well appreciated, the same plants have a wonderful facility to transpire at normal high rates when drought does not prevail! 

Cacti in Madeira botanic garden will also dehydrate the soil
I acknowledge  there will be some circumstances where ground cover is subjected to drought (drought that it has itself helped to create!) or starts to go dormant, that its leaves will start to act as a mulch.
There was some dispute about this post - which I welcome - in my comment column. I (inadvertently) failed to reveal an argument contrary to my case, On hilly sites ground-cover has a significant role in reducing run-off in heavy rain.
A more exotic fact that illustrates nature’s wonderful diversity is that some desert plants are capable of absorbing sea mists and exuding water into the soil.

Ground cover is beautiful, is horticulturally and ecologically beneficial but does not usually conserve water.

Gardeners are told to dig to aerate the soil. If there is any validity to this nonsense there has been something very wrong with their previous soil management!

The dust mulch theory is very plausible. Fortunately for someone like myself who believes excessive soil cultivation damages the soil, the dust mulch story is almost completely wrong.

Dust mulching is the idea that cultivating the soil surface reduces water loss. This must not be confused with the horticultural truth that when the soil surface is dry it starts to act as its own mulch and reduces water loss by evaporation to almost zero - only to continue when the soil  surface is re-wetted by rain or irrigation. In contrast, water loss by transpiration from the plant continues until roots fail to find water.
Leaving aside the fact that many gardeners overuse fertilizers (and some fail to use fertilizers when they would be extremely beneficial) this post challenged the notion, dear to the heart of vendors, that every plant needs its own special potion. In a different post I discussed whether a special fertilizer was needed for the lawn.

Not all myths arise from ancient tradition as illustrated by this modern meme about rhododendrons

Some items of misinformation are discussed in posts not in my myth series. Many gardeners fail to understand the terms texture and structure when describing a soil. My recent post on mistletoe mentioned four different myths associated with this plant!


  1. I always feel so sorry for those little orange centipedes.

    Thinking of the really useful information you have on your blog have you ever considered creating pages to your blog with tabs to open them at the top. This post would make a great page serving as an index to your other articles. I know what you will say but you could ask Cathi.

    1. Thanks for this Sue. my son has explained to me what you mean! it seems a good idea. i will ask Cathi about how to do it.

  2. Roger, you are a bottomless pit of useful information - in which many people will benefit from diggng!

    1. Thanks for the compliment Mark, i have to admit as a none digger I am particularly talented at digging a hole for myself!

  3. Can you explain why the soil is always nice and damp under forget-me-knots and limnanthes (both ground cover of sorts) but as soon as I remove them the ground surface dries out. It has made me consider using either of them as a winter cover on a vegetable patch as they seem to keep the soil so moist.

    1. What an interesting question Pauline. I hope you have linked back to my orginal post. Your comment based on close observation is like dear old ‘Chalky’ White,in my story, saying the old man is wrong.
      I agree that your limnanthes and forget-me-nots are a ground cover and I think you might know I have a lot of both of them in my various gardens. I love them but not for water conservation!
      Under your plants it will be moist at the immediate soil surface because of shading and protection by the leaves and this will persist for a short time -a little longer than a bare soil drying - and of course it will be rewetted if it rains. I have conceded in my orginal post that this might sometimes be beneficial and even get seeds going like the hellebor self sown in the middle of my clump of ground cover in the original picture.

      What you do not see is the enormous amount of water being sucked out of the ground from depth and lost by the leaves. If you were to pull out your forget-me-nots in April after they have flowered and it is a normal month for rainfall, you might very well find you soil bone dry down to about fifteen inches and with many other plants dehydrated to very much deeper.
      (Not that I would ever pull out all those lovely roots that as they decay contribute to soil fertility)
      Your idea of using your plants as a green manure is a good one. If you google my post on green manure you will find that I am a big fan of quite a number of unconventional green manures. The dehydrating effect of green manures is sometimes overlooked by gardeners however.

    2. As I have heavy clay soil and springs, at the moment I would be thrilled to suffer from a bit of dehydration. All newspaper burials have been suspended until further notice!

    3. Sorry you have a drainage problem Sarah. Two of the three classical causes of drainage problem in one garden!
      Although your comments are light heartedly made, you have as usual, brought in some interesting points.
      I can't promise you much extra dehydration with ground cover at this time of the year as the rate of water loss from a ground cover of leaves is very similar to wet soil. It's when the soil surface is dry and self mulching that the water loss from the leaves races ahead of that from the soil.
      As to your newspaper burial…. Although burial of newspaper does increase overall water holding capacity it will not adversely effect the rate of water loss of surplus water above this. Your clay soil and springs are your problem. The paper will not help or hinder, although in my own case it does help because it has enabled me to have beds raised in level above any temporary standing water.

    4. It's not all bad news, it's on a slope so I should be able to work around the problem, but it's early days yet. Slightly raised beds are what I'm aiming for too with the newspapers. I'm also trying burying wood, which is hugelkulture method, and seems very similar. I'm expecting wood to loose height more than newspaper, but it's very useful way to get rid of knotty bits of wood we can't split, so worth a try too!

    5. Shooks I have not written a burying wood post yet!
      Sloping slopes bring very subtle drainage problems that some gardeners do not recognise. Challenges bring opportunities Sarah!

    6. Sloping slopes indeed! A bit tautological, sorry!

  4. Here the water table is very high from November to May so I have to have raised beds. I think it would even stay high in summer if we were not that we are in the middle of a field (slowly turning into a forest) and all the plants surrounding the garden soak up a lot of water once they are growing.

    1. I bet some of those plants that tolerate the winter wet will love it in Summer Alain

  5. Great post and good that you linked your previous posts Roger - I was able to catch up on some that I hadn't read.
    I was once told that planting a tree in an area that is too wet (both high water table and poor drainage) would help reduce the amount of water retained in the area. Is this true or a myth?
    I'm doing a bit of reorganising in the garden and am considering planting a tree to help with my excess water problems.
    I feel that addressing the drainage would be a waste of time/effort/money as none of my neighbours would do the same - therefore any attempt would be futile.

    1. I fear that if your neighbours do not contribute to your effort you are right in your fears.
      Undoubtably large trees mean that you will go into winter with a large soil moisture deficit and this will help defer over wetting in Winter. Better if the trees are evergreen because they will continue to lose water in Winter.
      Sometimes tree planting will overcome a drainage problem but where drainage water continues to be received from adjacent land the problem does not go away

    2. Thanks for that Roger - I appreciate your time in answering my question, especially as I was slightly off topic.
      There would be no way my neighbours would address the situation - they are not keen gardeners.
      As Rick has said below - planting for the situation is the best solution and as I've already started to do that and am already benefitting from healthy plants, it's the right way too go.

  6. I agree with Sue, put these in tabs. They will be more accessible to Google searches with a higher Google ranking.

  7. I have not commented on your retrospective post so far, to be honest, because I wholeheartedly agree with pretty much everything that you say plus I have taken my time reading all the excellent earlier posts. There are a couple of things I would like to pick up on however, the first being that, on the subject of ground cover, you refer to the ground being depleted of water for a fair depth under Myosotis, I have always thought of the majority of effective ground cover plants as being fairly shallow, but often densely rooted particularly in the case of Epimediums, and therefore not affecting the available water to those adjacent deeper rooted specimens which I have always thought makes them most effective. In the case of planting to help cure a drainage problem I agree 100%, you can plant a willow in the middle of a bog and it will probably thrive and reduce the amount of water in the soil slightly, but what is the point as the problem will not be solved. The answer for the true gardener is to work with the conditions you have and develop the area with plants which will grow in that environment, the soil can be improved with the addition of grit for example but then the planting must be done with those subjects that are suitable and ultimately rewarding.
    Here is another myth that needs putting to rest, pot washing, particularly with the amateur gardener is a complete waste of time, as you can guess this is a heartfelt subject from my days with the parks!
    All the best for the New Year.

    1. Further to your comment about trees dehydrating the soil I have been reading an article in today's New Scientist about how many present day bogs started in the Bronze age when the ground started to wet up following deforestation

  8. I have been hesitating about posting about my complete lack of garden hygiene such as pot washing! There is a type of hygiene however I am very keen on which is eliminating sources of infection of such as white fly, RSM and similar by throwing out infected plants- more to come!
    Yes we washed the pots with cold water at Hartlepool,parks. I remember sitting on the steps of the potting shed washing.....

    1. I'm glad someone else doesn't wash pots - I always feel I should when I rread that others do but i just can't face it and we seem not to have any problems. I usually brush pots out before using to remove any rings of fertiliser etc.

    2. Perhaps I will diminish my credibility even further by admitting that often when I pot sometimes there is even a little soil left in the pot!
      In a very early post 'Breaking the rules' I explained how I use my sandy soil as potting compost and it is repeatedly recycled! I will return to this theme in three posts time!


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