My Monstera puts out big leaves but they have no splits. What actually triggers fenestration?

Fenestration is a light and maturity response, and light is the part most people get wrong. Monstera deliciosa produces entire leaves as a juvenile and begins splitting them only once the plant has enough energy income to justify the cost. In a dim room it will keep making large, whole, thin leaves indefinitely because the cheapest way to catch scarce light is maximum unbroken surface area.

The practical threshold is brighter than most living rooms. Aim for a position that reads roughly 2,000 to 3,000 lux for ten to twelve hours a day — in plain terms, within a metre of an unobstructed east or north window, or two to three metres back from a south window with sheer curtains. If you can read a paperback comfortably without a lamp all day, you are in roughly the right range.

Maturity matters too. Splits typically start once the plant has produced several leaves from a thickened stem with visible aerial roots. A cutting rooted last spring will not fenestrate this year no matter what you do.

Support is the underrated factor. Monstera is a hemiepiphyte: in the wild it climbs, and climbing is the signal that it has found a trunk and can commit to adult foliage. Give it a moss pole or a slab and let the aerial roots actually attach — keep the pole damp so they grip rather than curl away. Plants left trailing across a shelf often stall at juvenile leaves for years.

Feed lightly during growth and do not repot into something enormous. A pot that is too large stays wet, the roots stay small, and leaf size and splitting both stall.