Yellow leaves mean different things depending on what other symptoms the plant is showing. Sometimes mature leaves will turn yellow and die off, purely as part of nature (similar to how we break fingernails or have hair loss!) however, reoccurring or large mass yellow leaves can indicate an unhappy plant. Overwatering, underwatering, nutrient deficiency, sunburn and pests are the usual culprits of why leaves turn yellow.
Below, we’ve also listed other signs to look out for if you spot reoccurring yellow leaves
Yellow leaves with deformities
Yellowing and leaf deformities, particularly on new leaves, is usually caused either by a pest or a mineral deficiency. Check for pests such as spider mites, mealybugs, aphids etc and treat with a pesticide spray. If no pests can be found, this may be a nutrient and mineral deficiency, usually calcium or boron.
Solution: Spray pests, fertilise monthly, repot with new soil.
Yellow leaves fading to a bright yellow
Check the soil - if it is wet or heavy (and you haven't watered for a while), the plant may be overwatered. Check the base of the stem too, if this is black the plant is most likely suffering from root rot.
Solution: Repot immediately with new soil, water less and let the soil dry out, and try using a terracotta pot (as this absorbs water from the soil). Also remember: Never plant your plant directly into a ceramic pot with only one or two drainage holes!
Majority of the plant is turning yellow & dropping leaves
This is most likely a temperature issue - it's either too cold or too hot. The yellowing leaves will be more pale or white.
Solution: Watch your plant throughout the day and make sure there isn't any direct sun hitting the leaves, or airconditioner vents blowing cold dry air onto your plant.
Majority of the plant is turning yellow but not dropping leaves
This could mean the plant is pot-bound and the roots have no room to grow.
Solution: Repot to a bigger pot, add fresh soil and include fertiliser.
Yellow leaves also curling/drooping/crisping
If your plants yellow leaves are also curling or have crisp edges, test the soil - if the soil is dry, your plant is most likely under watered. You’ll likely see older, lower leaves dropping as well.
Solution: Give your plant a big drink or even sit it in a bucket of water overnight to help it recoup!
One or two old or mature leaves yellowing
As plants mature and grow, older leaves can age-out, start to yellow, and eventually fall from your plant. This is natural leaf shedding. If your plant is happy and healthy otherwise, and only older, mature leaves are yellowing and dropping, there is no need to worry!