Darryl’s Analysis

Environment:
These windows are great for the plant – light is good.

Effort:
If the plant is receiving several hours of direct sun, its soil is likely reaching “completely dry” well within a week.  This is why the rule for watering “once a week for Monstera” does not work – it does not account for varying light situations.  On the other hand, by determining when to water based on soil dryness observation, you may notice that the soil reaches around halfway dry within 3-5 days.  So a better “rule” for watering is “water a Monstera whenever its soil is about halfway dry.”

Reminder: the degrees of dryness you need to know are just these broad categories – (1) fully saturated (like right after watering), (2) halfway dry, (3) completely dry.

Given this strong light, your plant is growing vigorously and would benefit from being repotted into a larger pot with new soil.  Go up to a pot size that is roughly the same diameter as your largest leaf (probably 12-14 inches).  Potting mix: peat moss/coco coir + perlite + bark chips in a ratio of roughly 2:1:1.

Expectations:
Unfortunately, there’s no way to reverse this yellowing even if you repot immediately.  After a few months, the leaf will become completely yellow, at which time you can cut it off.

Going forward, your cue to water should be based on observing the soil instead of “the watering schedule for a Monstera”.  You will enjoy the Monstera in the long-term!

Learn my long-term enjoyment approach to houseplant care – learn from my course.