Sunday, January 1, 2017

Tree Root Problems

Trouble with foundations, sewer and water wipes, footpaths, fences?
   I would like to know what other people’s experiences are. There must be a lot of knowledge out there about Australian native plants growing near built structures, but it’s hard to find it.
I got curious about the subject because one of my readers asked about about her kurrajong Brachychiton populneus. She has it planted 10 feet (3 metres) from a porch. Her husband wants it removed, as he is worried that it might affect the foundations. She would like to believe that it is far enough away to be of no concern.
   I would have thought 10 feet was far enough. This is a drought hardy tree which has evolved to survive by putting its roots deep, unlike Brachychitons from wetter parts of Australia, which might have shallower roots and be more of a problem.


The owners of this house at Inglewood didn't seem to have any problems with their kurrajong, and it looks as though both house and tree have been there a long time. What wonderful shade it gives, on a hot summer's afternoon.
 
   I went looking on the internet, thinking recommendations for suitable distance from structures, for planting various species, would be easy to find.
   Not so!
   I found various lists of recommendations, but the differences between them were so great as to be ludicrous.
   In the case of the kurrajong, I found that Western Water (a water authority near Melbourne, which surely cares that its users don’t wreck their pipes with careless planting), lists kurrajong as one of its "acceptable plants near sewer lines" so long at it is 2 metres away from the pipes. It is interesting that they don't list any other Brachychitons as "suitable".
    The Australian Plant Society recommends the kurrajongs should be placed 3.5 metres away (the same recommendation as it makes for some other, less drought hardy Brachychitons. Are they really all the same?) An East Gippsland site thinks they should be 4 metres away. A Western Australian water corporation recommends 6 metres. Bundaberg Regional Council doesn't think they are safe unless they are 10 metres away. One site makes a blanket recommendation that all trees should be planted a distance 1-1.5 times the potential, full-grown height of the tree away from all structures!
   What boring places our suburban gardens would be if we all took his advice.

   So what is your ordinary person to make of this? Do these people really know their stuff? If so, which ones? They can't all be right.
   Well there are some obvious clues that let us know which advice we should take with a grain of salt. Clues to the clueless are:
a. They have a blanket rule for all trees, whether or not they are species which would really be surrounded by a wide circle of shallow roots equal to the tree's height (possible with Eucalyptus trees) or more likely to have roots which plunge deep in a narrow root-zone, (like dry rainforest species).
b. They don't supply botanical names, so you can be left in doubt as to which plant they are talking about. If they do give a botanical name, it is the name of the genus only, and then we are warned against the lot as if they were all the same. No, a little Meleleuca thymifolia is NOT going to cause the same problems as a whopping Meleleuca quinquenervia. To say that "Melaleuca sp." should be kept more than 6m away from drains is not helpful!
c. They seem to be written by someone who doesn't know much about plants, but knows that he/she will suffer consequences, if the distance recommended is not big enough. Huge margins of safety probably indicate a less reliable site.
   Sadly, advice provided on these ill-informed sites must have caused the destruction of  many harmless plants. They are certainly no help to those of us who like plants in our gardens. We can't help but be very well aware that many of the plants that they warn us against are growing in gardens around us, causing no problems at all.

I did find some sites which looked as though they had been written by people who knew their stuff.
   The best of them seemed to me to be East Gippsland Water, at www.egwater.vic.gov.au/wp-content/uploads/2016/03/PlantThoughtfully2013.pdf  , and the Australian Plants Society’s Drain Cloggers page, at http://www.australianplants.org/fsjten.htm.
   However, even the best sites suffered from plant lists which were too small to be broadly helpful. Better to be silent than to spread misinformation, of course, but we could do with more, and more reliable, information on the performance of a wider range of Australian native species near built structures.

Can you help? 
   I would love to hear from experienced gardeners who live with gardens containing Australian native trees and shrubs, and are prepared to share the knowledge they have gained from practical experience.
  I feel sure there would be readers who  would like to hear it, too.
   I don’t just want to know about the problems, though that certainly helps. I also want to know what plants can tentatively be classified as not too risky. What grows close to your house / footpath / drive / water-carrying pipes, and seems to be problem-free? 
   Please see my email address in the white column at right. I’d love to hear from you!
Or write a comment, but be warned that when you publish it, it won't appear at once.  I screen all comments first, and don't do it every day.


Thank you to  Lindsay Sutherland who wrote me a thoughtful email in response to this blog.
To quote from it:
Thanks for your blog about planting distances. I too think that safe planting distances from homes and other structures are hard to estimate. For example I planted a mango very close to our house. People don’t recommend this. I wouldn’t either if I was living in a hospitable climate for mangoes. Mangoes are very marginal and may not survive in our climate. The tree grows very slowly down here and will never be as big or as vigorous as mangoes grown in Cairns or Townsville. So climate is another factor to consider when recommending safe planting distances.Another consideration is soil type. I live in a heavy clay area. Poor drainage can deprive plant roots of oxygen. Clay can prevent or slow root development. So trees growing in high clay soils may possibly be planted closer to a home. Some native trees I am growing under a huge oak tree from next door are:-
Hymenosporum flavum, 4-5m tall, 6m from house
Backhousia citriodora, 3-4m tall, 5m from house
Capparis arborea, under 0.5m tall, 6m from house, very slow growing
Clausena smyrelliana, under 0.5m tall, 5m from house
Ficus coronata, 3-4m tall, 3m from house, adjacent to driveway

If trees are pruned and clipped some of the roots may also be reduced or at least their growth rate is reduced. The focus of much science of plants is on the easy to access leaves, flowers and fruits of a tree. Very little description of roots is made simply because it is much harder to do so and likely will destroy the tree. Science of root development is at an earlier stage and understanding than science of leaves and other above ground plant parts."
And a reply from the blog author: All good stuff, especially the comment that trees which grow large in one climate might be smaller somewhere else. We on the Darling Downs are very familiar with this phenomenon, as specimens of trees which are larger in the better rainfall of the coastal strip are always smaller here
I am not too sure about Lindsay's theory that heavy clay makes it safer to plant close to a house. Some plants respond to moisture-retaining soil by spreading their large roots out on the surface, instead of diving deep looking for moisture (as we see in wetter rainforests). The cracking clay of the Darling Downs is very fierce in its effect on surface roots every dry season, but if the clay spends more time being damp right up to the surface, it might be another matter.
As Lindsay said "Safe distances are hard to estimate". But like him, I think we can have take a few informed and cautious risks, for the sake of a lifestyle with beautiful trees. 

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