On 15/11/2017 14:15, Andy Burns wrote:
Martin Brown wrote:

Watering with a solution of sulphate of iron will kill it. It goes
black, as do your hands if you get it on them.

Your hands and any paving you get it on will go rusty orange (or at
least they should do). Silver nitrate makes hands go black

Splashes of Iron Sulphate made my neighbour's fence go black.

That is iron stain from tannins in the wood - same as classic blue-black
writing ink formulations of old which used oak galls for tannin.

--
Regards,
Martin Brown