Reddish stems on some varieties are also a natural occurrence.
Yellowing stems can result from overwatering, too much sun, infection, and poor nutrition.
What Is an Orchid Stem?
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The orchid stem is the base of the plant where the leaves and flower spikes growth begins.
The part of the plant that produces flowers (the spikes) is sometimes erroneously called the stem.
The spikes die back naturally when flowering is complete and is not a cause for concern.
A healthy main stem enables photosynthesis and supports the growth of the entire orchid.
Overwatering
Overwatering is an underlying cause of many orchid problems including yellowing stems.
Water displaces oxygen causing the stem to lose healthy green tissue.
If you suspect overwatering, remove the orchid from its pot and inspect the roots.
White, mushy roots indicate it’s getting more water than it can absorb.
Give it time to recover.
This may take several days to several weeks.
The heat generated by direct sunlight may also cause insufficient moisture.
Water the orchid thoroughly and allow the excess water to drain.
Move the plant to a cooler location with indirect light.
Withhold fertilizer until the stem regains its green color.
Orchid potting mixes can support nutrition but provide very little actual food.
This makes supplemental feeding (fertilizing) important and necessary.
Nutrition deficiencies develop when the plant gets either too much calcium or not enough nitrogen.
Hard water raises calcium levels and nitrogen is the element that supports healthy green foliage.
Fertilize monthly until you see new, healthy green growth.
Fertilizing can be increased to bi-weekly once the orchid is actively growing.
It’s a common practice in orchid care to reduce both watering and fertilizing during this time.
Immediately isolate the plant.
Remove it from the pot and inspect the roots, removing any that appear black or mushy.
Random yellowing or dark spots on leaves can also indicate infection.
Treat all cuts with a cotton swab dipped in hydrogen peroxide.
Allow the plant to recover.
If the stem on a single-stemmed orchid continues to deteriorate and turn black, the orchid should be discarded.
Stems on monopodial, single-stemmed orchids should not be cut off.
This can lead to irreversible damage which the orchid cannot survive.
A yellow stem does not always mean that an orchid is dying.
A flower spike, sometimes called a stem, turns yellow and falls off naturally.
If they aren’t plump or feel mushy, the plant is getting too much water.
Early signs include limp foliage and soft tissue at the base of the stem.
Royal Horticultural Society
A New Fertilizer Without High Phosphorus Proves Itself with Orchids.American Orchid Society
