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A family member wants to put up a fence behind her condominium and the plans state that the fence will be 3 foot away from a small maple tree in the back yard. The association members say that this is too close to the tree and it will do harm to the tree.

What is the perfect distance away from the tree to dig to put in the fence post?

  • Need more detail - what kind of maple (Acer palmatum or another kind altogether?), how long's the tree been in situ and what is its current height and spread? – Bamboo Nov 8 '13 at 19:56
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Please don't repeat the dripline myth - as a landscape architect I'm continually trying to to protect (and repair damage to) trees where the roots have been cut back to the dripline. The system I use is called the Critical Root Zone system (a utility standard in the UK) and is quite simple to work out:

Measure tree trunk diameter at 1.3metres (52 inches) above ground and multiply this figure by 29.5, the answer is the radius of protection you should allow for (this works for most tree types from narrow to broad canopies). If the tree has plenty of lawn space on one or more sides you might get away with cutting some roots, but where does the dominant wind blow from? because if you cut off all the roots on the windward side of a tree you risk it blowing over.

You should think about varying the spacing of fence posts in the vicinity of the tree, and digging the hole carefully by hand. Also what season is it where you live, autumn is the best time for this.

And finally you should consider the tree's monetary value - how much value is the tree adding to the total property value? Can you afford to lose this tree or will it chop $10,000 off your house price - just a few thoughts.

  • In my answer I point out that the drip line only encompasses up to one third of the roots. I am interested in the Critical Root system you refer to. Can you add to your answer with a reference to it? – kevinsky Nov 9 '13 at 15:53
  • I was going on memory above and a bit out but see these refs:CRZ method AS4970 2009, radius = DBH * 12: Australian Standard, Protection of Trees on Development sites_AS4970_2009. root protection zone, radius = DBH in centimetres * 0.18m: Harris, R., J. Clark, and N. Matheny. 2004. Arboriculture: Integrated Management of Landscape Trees, Shrubs, and Vines. 4th edition. Prentice Hall, Upper Saddle River, NJ. mean root spread of many deciduous trees is 2.9 * dripline diameter: Gilman EF. 1988 Predicting root spread from trunk diameter and branch spread. J. Arboriculture. 14. 85-9. – nigelc Nov 10 '13 at 13:13
  • Any advice on how deep one can safely dig (doing some root damage in the process perhaps) based on other input data such as tree height, canopy, age, sun exposure, etc ? - I am asking about a pear tree 8 years old standing about 4 meters tall with not much canopy- perhaps 1.5 meters. And about some other two deciduous trees 20-30 years old, 5 - 10 meters tall and 6-7 meters canopy. Thanks! – kellogs Apr 20 '15 at 19:52
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For a well established tree you can use the distance from the drip line. This is the point at which the tree's branches and leaves extend to. However this area is likely to only include half the tree's roots. As this publication advises:

Roots normally grow outward to about three times the branch spread. Only 50 percent of the trees root system occurs between the trunk and the dripline. Roots on one side of the tree normally supply the foliage on the same side of the tree. When the roots on one side of the tree are injured the branches on that side of the tree may die back or drop. With some trees, such as maple, the effect may develop anywhere in the tree canopy.

And as Bamboo points out this can all be influenced by the age and type of tree and the soil conditions. A tree that is already stressed will react poorly to root loss.

Digging three feet from a tree is definitely too close. Damage is likely. What cannot be determined is the extent of the die back and if subsequent regrowth will hide it.

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