Repotting the monstera into a pot that was too big
The monstera had roots coming out of the drainage holes and pushing up through the surface, and it had tipped over twice in a week, so a repot was overdue. I made the classic mistake and I knew I was making it: the new pot was 14 inches across, up from 10, because I wanted to do this once and not again next year.
The move itself went fine. I soaked the plant the night before, slid it out, teased the outer roots loose and cut off two that were brown and hollow. The new mix was two parts a general potting soil, one part orchid bark and one part perlite, which drains fast and holds enough air that I could see light through the pot sides when I packed it. I staked the main stems to a moss pole and watered until it ran clear from the bottom.
Then it sat. For three weeks the soil stayed wet. The meter read moist at six inches for twelve days when the old pot would have been dry in five. The leaves drooped slightly and two of the older ones developed yellow patches at the edges, which with a monstera usually means the roots are sitting in water for too long. There is simply too much soil for the root ball to drink from, and the soil that has no roots in it stays saturated.
I did not repot again. Instead I tipped the pot on its side to let it drain better, moved it closer to the window to speed up evaporation, stopped watering entirely for two weeks and pushed a wooden skewer into the soil in four places to let air in. After about five weeks the soil reached a point where the meter read dry at four inches, and I watered lightly, only around the root ball rather than the whole surface. The yellowing stopped. A new leaf came in October, with three splits.
The rule I should have followed is the usual one: go up one size, two inches at most, even if it means doing this every spring. The oversized pot will be fine in a year when the roots have filled it, but the year in between is a slow test of whether I can leave a plant alone. So far I am passing, barely.