On 17/08/2020 18:54, Graeme wrote:

About five years ago, my neighbour had a group of the above seriously
trimmed, and gave me a large pile of chippings which have sat against a
wall in my garden ever since. Investigating that pile recently, I find
a lot of the chippings have broken down to a very friable condition.

However, said pile is also a mass of roots, which have grown up from the
trees next door. I have pulled out the larger roots, but there are
bound to be smaller lengths remaining. Were I to use that material as
mulch, or just dug into my garden, are the roots likely to die and rot,
or am I likely to be cursed with a million little horse chestnut trees
popping up for the rest of my life?

There are lots of hits on a web search for stump-grinding horse chestnut
trees. If this left actively growing roots in the soil I am sure we
would have heard about it by now. There are some plants which can be
propagated from root cuttings, but although it can be done with Horse
Chestnut it's pretty rare, for example see
http://agro.icm.edu.pl/agro/element/bwmeta1.element.agro-article-db112e8f-51c8-48f8-8716-163a8cd6a549/c/8-5Czek.pdf

I can't see you getting lots of little horse chestnut trees. Are you
sure the roots coming up are from horse chestnut trees?


--

Jeff