Lucky Bamboo with Yellow Stems
A yellow stem is more serious than a yellow leaf. It is more important to find the cause then saving the victims. The rest of the stems are at risk. Check for any changes in the normal growing environment. The easiest cause to find would be that the stem was not in the water through low water level or the stem had been shifted.
Remove the yellowed stem and quarantine it in a separate vase away the area where there are healthy plants. If the stem was part of an arrangement, you must wash the healthy plants, vase and filler with a mild hand dishwashing soap. Make sure that the stems do not feel slimy of have soft parts on their stems. Wash till all of the slime is gone. Remove the stems that have soft spots, these will probably turn yellow.
Reverse any changes in the normal growing environment and move toward the ideal growing environment. Watch these carefully and change the water more frequently till the danger has passed in three to four weeks.
Where the yellowing started is a clue to where the problem is.
Too much sun
Spider mites, scale or other insects
Broken or damaged stem, wire tie too tight
Stagnant water or too cold
Not enough fresh water or chemicals in the water
Microbes, fungus, slime, insect larva, root rot
Not enough sunlight
Too much fertilizer
The yellow part is dead. Nothing is going to bring it back, but the rest may be saved. Lucky Bamboo is tough and can be propagated from pieces.
Wash the stem in mild dishwashing soap. Leave it soaking for five to ten minutes. Feel the stem for soft spots that are still green. The soft areas will turn green in the near future. With a very sharp knife or razor blade cut the stem through a section where it is still firm. Check the cross section, if the center is soft, make another cut till the center is firm and not discolored. The stem part that you have left can be put into water and it will root or sprout if kept warm and in indirect sunlight. Just to be sure, keep it under quarantine until it recovers.