By Pmulvenn
United Kingdom 
I have 2 well-established Leylandi in my smallish back garden, and as a fence was added after they were planted, one is superfluous. In addition, the roots are extending beneath where I now have a garden shed. I have cut down the unwanted tree so that only the trunk remains. If I leave only a stump, will that stop the roots growing, or would that require the tree to be killed by the use of some chemical or other? If so, which chemical would do that.
6 Jun, 2013
Answers
We cut down a whole row (16) of HUGE (40') inherited leylandii two years ago, leaving 3' bases to nail a fence to, and have never seen a single bit of regrowth. Go for it!
7 Jun, 2013
Thanks very much, that's simple to do. I've now cut it down to about a 3" stump, so hopefully that will be the end of it.
10 Jun, 2013
Leylandi will not regrow from an old stump as long as there's no green leaf growing from it. So you don't need to add any chemicals . The roots will die and eventually rot.
6 Jun, 2013