Roots grow... deeper or wider?

[namnhi]

This seems to support wider than deeper.

 

[Shibui]

This can also be seen when observing trees blown down in storms. Actual depth of roots will depend on the local environment, soil type and species of tree but I agree that roots are far more shallow than most of us were led to believe.
Note that he mentions roots in the top 3 feet of soil. Even if that's less than we imagined it's still a fair depth.
That depth doesn't seem to reduce in direct proportion to the size of the tree so unrestrained bonsai roots and roots of trees in grow beds will still grow down to 3 feet unless we manage them.

 

[Cajunrider]

I have seen many uprooted trees in the Gulf Coast from TX to FL. With the exception of trees growing on high elevations that has to go down further to find water, all the trees I've seen have their roots stop right at the water table. On my land, in the summer I have to dig about 2.5 ft and I see water. Hurricane Laura uprooted 30 of my neighbors' trees and 2.5 ft were where all the roots stopped.
In Ohio and Kentucky where I have had chances to do tree works, the trees on the hills have much deeper roots. I think trees just keep growing roots until they find sufficient water to live.

 

[Paradox]

depends on the tree and the soil/area its in