I would not use roundup or any other herbicide on moss in a bonsai container, period. You're flirting with disaster.

Simply pulling the moss up by hand is the simplest and proably most effective way to do it. You have to keep at it for a season, but once you've got it on the run, it can be controlled.

I'm not sure how effective Roundup would be on it anyway. That stuff was formulated to work on grasses and weeds by overloading the leaves with rooting hormone, from what I've heard. Don't know if sagina has the same hormone buttons...

Mark,
Thanks for the reply!
Joe

To be on the safe side, Mark is probably right, but from time to time, I'll have a plant in a nursery container that is badly matted with Scotch moss & no amount of pulling seems to be effective. I also had plants that I planted in the ground that developed a solid mass of this weed at the base.

Round-up is a non-selective herbicide that is absorbed by living plant tissue - primarily leaves. It is often used around recently planted trees to eliminate competition from weeds or on established trees for appearance when it's desirable to eliminate surrounding vegetation. I sometimes use it to control weeds in containers as well as plants growing out. So far, I have seen no ill effects, but ....?

First, I water the plant well. I cut a piece of cardboard to fit around the trunk & use it to push foliage up & out of way. I then spray the Round-up so a fine mist covers the weeds, being careful there is no stray aerosol contacting leaves of the plant I'm spraying or other, nearby plants, and that there is not enough spray so that it runs into soil. For the next couple of days, I'm careful about not watering the chemical into soil. Round-up breaks down quickly under normal growing conditions & after a couple of days I return to normal watering.

Though I haven't experienced any harm, I don't use it on trees that are in bonsai pots or developed to the point they are ready to go in pots. There is always risk involved with its use - you'll have to decide for yourself if it's worth it.

Al

A little trick my lawn maint. people showed me is to put on a latex glove, then put your gloved hand into an old sock. Wet the sock with the "ROUNDUP"(not to dripping condition) and wipe the plant leaves that are undesirable. This is an exceptionally selective method of herbicide delivery.

Regards,
Dave

I've done that using a jersey (cotton) glove & found it to be much more effective if, at the crucial moment you chant, "I smite thee with the hand of death."

Al