GM! That yellowing leaf on your plant, it's a goner. It isn't going to turn back to green and it isn't producing energy for the plant anymore so pull it off gently or snip it off with sterilized scissors.

Reasons for yellow leaves

Aging leaves - usually the lower leaves are the oldest

Overwatering- multiple leaves will yellow at once.

Check the soil, drain saucers/pot, check for root rot, stop watering, reduce lights, keep temp warm.

You can also change the soil, or increase air circulation and also put tampons into the soil to absorb excess water!

Underwatering - drooping/wilted leaves, soil has hardened, has cracks & if there is a gap between the soil & the pot your plant is severely dehydrated

Fill a bucket with some , put the plant pot in so it can absorb through the drainage holes. Leave for 30min. Remove & drain

For most houseplants, stick a finger 1" into the soil. If it is dry your plant needs water. Or you can purchase a moisture meter that you stick into the soil a d it will tell you “wet,” “moist” or “dry."

Humidity - Some plants prefer higher humidity. If the leaves are turning brown at the edges or curling up, it may be because the humidity is too low. Group plants together for a slightly higher humidity microclimate. Add a humidifier for a bigger boost in humidity

Pick up your plant pot, before and after watering. After a while, you can judge the soil’s moisture content just by the weight of the plant. When the plant feels light then it's time to water!

Water Quality - Some plants are more sensitive tap water that contains chlorine or chloramine & salts from fertilizer can accumulate in the soil too. This stresses the plant and you get burned (yellow) leaves.

Flush salts by running extra water through soil & drain when watering. Use dechlorinated water, rainwater, or aquarium water. Or let your tap water sit in a bucket for 24 hrs before watering.

Lighting - Too much or too little light can cause yellow leaves.

Too much direct light dries out or scorches leaves with yellowing. Too little light, the leaves will be yellow but still hydrated and will yellow on the side of the plant furthest from the light.

Rootbound plants - if the pot is too small & there is no room for the roots, leaves will yellow because of the lack of oxygen/nutrients
Repot into a larger container
If you don't want to move up in size, prune your plant & roots. Or divide and propagate (depending on the plant)

Over Fertilization can also cause yellowing and leaf burn.

Nutrient Issues - nutrient deficiencies can sometimes cause leaf yellowing. make sure it isn't any other issue before fertilizing your plant unnecessarily.

Common deficiencies:

1) Nitrogen (most common) – general leaf yellowing starting with older leaves

2) Potassium – turns the edges of older leaves yellow

3) Magnesium – starting with older leaves, yellow that spreads from the center of the leaf outward with the veins staying green

4) Sulfur - yellowing starting on younger leaves, spreading to the rest of the plant

5) Iron - starting on younger leaves, yellowing with green veins

pH - regularly flushing the soil prevents build-up of fertilizer salts that can cause pH issues and yellowing

Drafts/Extreme Temperatures-
Cold temperatures cause leaves to turn lighter yellow and drop

Move plants away from air conditioners or windows and exterior doors during winter. Also move them further from Windows and direct light during the summer to prevent burning of the leaves

Transplant Shock -some plants are more sensitive than others & can get transplant shock

After transplanting, do not fertilize, water too much, or move the plant around.

Some plants are sensitive from being moved from place to place (Fiddle Leaf Fig) if it's happy then leave it!

Pests/Disease - deformed, damaged leaves or yellowing in one area is a sign of disease or pests.

Inspect for pests, remove infected leaves & isolate the plant. Sterilize your scissors each time you use them (even on the same plant) to avoid spreading the disease.