First, check the soil. Push a finger 2 to 3 cm (0.8–1.2 in) into it and lift the pot. Dry and light means thirst. Wet and heavy means too much water or poor drainage.
Most likely cause
Thirst (underwatering)
How to tell
The soil is bone dry, and the yellowing arrives alongside crispy frond edges with dry soil rather than soft, mushy growth.
The fix
1
If the soil is dry, water thoroughly (every 6 to 8 days in summer is the usual pace for a blue star fern), then settle into feeling the soil before every watering rather than watering on a fixed day.
Other possible causes
Not a match? Compare the signs below to find the one you have.
Too little light
The yellowing comes with pale, stretched new growth leaning toward the nearest window.
The fix
1
Move it to a brighter spot, but keep it out of harsh midday sun, which scorches.
More about this
That combination shows that the spot is too dim for a blue star fern.
Overwatering & early root rot
The soil is still wet days after watering, the lower and oldest leaves yellow first, and the stem base may feel soft.
How to tell
Small dark flies around moist potting medium may be fungus gnats.
The fix
1
Stop watering.
2
Make sure the pot can actually drain, and wait until the top 2 cm (0.8 in) of soil feel dry: ferns don’t like drying out.
3
If the base is mushy or smells sour, unpot it and trim any brown, soft roots before repotting in fresh mix.
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