Of course anybody to whom allelopathy in
Juncus
maximowiczii is a life-fulfilling issue is free to pitch in. BRBR

If it were of no importance whatever, I would not have asked. It happens that
J. maximowiczii is a nice little companion plant for bonsai. However, I
discovered that if I planted it in the same pot with a bonsai group, once the
rush clump reached a significant size (2-3"), the nearest tree became ill. I
think I actually lost one. A Google search revealed that other Juncus species
have allelopathy, so I am assuming this one does too. From now on, I will
display it in a separate pot.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)