How frequently do you water the seedling? And how much sunlight does it get?
In general the potted avocado seedlings need more sunlight and moist soil (not saturated) to grow better. Over watering leads to yellowing of seedlings, so water only when it is necessary. Also provide proper drainage to the pot. It is recommended that when the stem is 12 inches high, cut it back to 6 inches to boost the growth of new shoots.
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