Question

Olive Tree   Hi,

I have a lovely giant olive tree in my front yard (Los Angeles, CA) which is easily over 50 years old. I'd like to make a flagstone patio set in concrete below the tree but want to make sure will not damage given diminished source of water. However, even with enclosed patio open soil will remain not far from trunk - about 4 feet on one side of tree in
adjacent bush line area which runs parallel around 17 feet. Also,
another patch of ground 15 feet away which should be a source of
water. Want to be safe however.


I have an existing irrigation system for this area of yard so possibly could add some source of water beneath concrete patio if you think that would be needed.  Also,  I could leave an opening around tree trunk if you think that would help.

Finally, one side of olive trunk is on lower ground and with new
retaining wall which shall join the elevated patio, want to level
entire area around tree. Therefore would be adding around 1-2 foot of
soil and probably some concrete around downside of one side of trunk,
above ground root system.   So wondering if covering this would damage tree causing dry rot and would concrete covering exposed roots be OK?

Appreciate any advice.

Thanks a lot,

TOM DREW

(323)665-3254

Answer
Olive trees are amazingly resilient trees and robust healers.  Their roots are extensive and shallow.  They are not sensitive to root disturbance like bougainvillea.  Though these lovely trees have a Spanish-Old California charm, they are messy, dropping blossoms, seeds, and leaves, discoloring and up-lifting any kind of flatwork that you may want to create underneath them.  

I would suggest a paver with sanded base.  Anything you affix in/with concrete will be torn up by the roots in a few short years, no matter how stout you make it.  I would further suggest that you pave no more than about half the drip-line area, because not only does the root system need water going down, but it actually needs air going the other way, too.  It doesn't need to be exactly 1/2 of one side, so long as you have pockets of bare earth totaling about 50% of the drip-line area disturbed or covered up.  Yes, leave some room around the base for the trunk to expand or it will do it for you; The hard way!  From the picture, about where the roots seem to transition downward, now - 2-3 feet, perhaps.  Don't pave right up to the wood, and don't raise the level of the soil past where the root & trunk transition - the slight color change.

Again, from the picture, filling and leveling to the retaining wall elevation doesn't look like it would be detrimental, either. the Olive a very stout tree. Remember that a concrete paver is about 4", and a sand base is about 6", so you're taking up almost a foot just with that material.

No additional irrigation needed, as the tree is already getting its water from the adjacent planter/lawn/flowerbed 15 to 20 feet away from the trunk.  In LA, you get about 16 inches of rain/year already, and that is sufficient for this Mediterranean tree.

More discussion:
http://patwelsh.com/wpmu/blog/trees/olive-tree-roots-invading-driveway/

I grew up in LA, and remember the old olive tree in our yard, next to the driveway.  It spewed discoloring seeds all over the concrete, so I would pick a paver color that is mottled brow/grey in color.  There are some paver styles that are 損ermeable? so you can slightly exceed the 50% rule-of-thumb.  Again, it helps that the Olive is a very resilient tree. There are products that will inhibit the olive production, but they are expensive and must be applied annually.

Here is a product example:
http://www.ehow.com/how_6028383_prevent-olive-fruit-olive-trees.html

Again, any kind of concrete work is going to be torn up by the Olive Tree抯 shallow but persistent root system, so I抎 suggest sand base with mottled-colored pavers. Raising the grade: no problem; Just not with concrete. Thanks for the picture & good luck with what looks like an exciting project!