I don't understand the problem: you wish to kill the trees then
cut them down? Cutting them down will likely kill them so why
bother doing anything extra. If you kill them then cut them down I
can't see how this will protect your patio, they'll still fall on your
patio.....
If you want to kill a tree I believe you "ring" it, cutting a ring
out of the bark and the live wood ( this years growth ) near the
base, so starving the tree of sap etc from the roots. To make sure I
believe you can buy some crystals to pour into the "ring", the garden
centre will have these.
If you are worried about the tree regrowing from the stump, not
all trees will do this - I cut an apple down last year and it's regrowing,
but my Leylandii firs die outright when cut off at the base. As yours
are firs you may get away with no regrowth without using chemicals.

Andy

"Steve" wrote in message
...
Hi all,
We have just bought a house that as a very nice patio but as two 8
foot fir tree stuck in it, we would like to kill these trees so we can
cut them down without disturbing the patio due to cost etc.

What would be the best way to do this i have been told several things
namely diesal in the ground or drill a hole in the tree and pour
diesal into the hole or another was using a very strong costic soda
solution to kill the tree slowly.
the ground will not be replanted or reused.

Thanks

Steve