What the holes in monstera leaves are actually for

The holes in a monstera leaf are one of those things people assume they understand. Most explanations you will find online describe them as an adaptation for wind resistance, or a way to let light through to lower leaves, or occasionally just “that is how monstera leaves are.” None of these are quite right.

The holes are not structural. They are not random. They are the visible result of a decision the plant makes — a developmental switch that only gets flipped under specific conditions, and one that the plant can reverse if those conditions go away.

Two plants in one body

A monstera growing on a forest floor and a monstera climbing thirty feet up a tree are not just the same plant at different sizes. They are the same plant in genuinely different developmental modes, producing different leaves, allocating energy differently, and behaving differently in almost every measurable way.

Young monsteras — seedlings, trailing plants, anything that has not yet found a tree — produce small, heart-shaped, un-split leaves. Simple, efficient, relatively unremarkable. This is the juvenile form. The plant in this state is essentially a crawler, prioritising stem elongation to search for a host over producing elaborate foliage.

Once the plant finds and climbs a tree, everything changes. Leaves expand. The characteristic splits and holes — technically called fenestrations — appear. Stems thicken. Internodes shorten. The plant switches from nomadic crawler to committed climber, and it reorganises its entire growth programme around that new mode.

The transition between these two forms is called heteroblasty, and it is not just a matter of age. A thirty-year-old monstera kept in a hanging basket, with nothing to climb, will continue producing small juvenile leaves indefinitely. The switch requires a specific trigger.

What actually causes fenestration

When aerial roots find a rough, moist surface and make contact, they begin to produce a hormone called cytokinin at their tips. Cytokinin is transported upward through the stem to the growing point, the shoot apical meristem, where leaf development is being planned.

In juvenile plants, the hormonal environment at the growing point is dominated by auxin — a different hormone that promotes stem elongation and keeps the meristem in an undifferentiated, generalist state. High auxin, small plain leaves. The plant is still searching.

When cytokinin from attached aerial roots floods the system, it overrides the auxin-heavy profile. The shift in that ratio changes what the meristem produces. The next leaf that develops does so under a new set of instructions: grow larger, develop lobes, initiate programmed cell death in specific zones.

That last part is what creates the holes. The fenestrations in a mature monstera leaf are not missing pieces — they are places where the cells were instructed to die. The plant builds the full leaf structure and then deliberately removes sections of it. The “holes” are intentional.

What the research has confirmed is that you can mimic this artificially. When scientists applied cytokinin directly to juvenile monsteras — bypassing the need for root contact altogether — the plants began producing larger, split, fenestrated leaves even without climbing anything. The climbing signal is, at its core, a cytokinin signal. A healthy root tip in contact with a moist surface is the natural source of that signal.

What this means in practice

The practical implication is direct: if you want fenestrated leaves, the plant needs attached aerial roots. Not just a tall pole — roots that are in contact with a surface moist and rough enough to grip, sending the cytokinin signal upward.

A smooth, dry bamboo stake provides vertical support but not the contact cue. A dry moss pole provides texture but, if desiccated, offers nothing for the roots to respond to. The combination of roughness and consistent moisture is what triggers the root tip activity that produces the hormone.

This is also why fenestration can reverse. If aerial roots lose contact with the pole — because the moss dried out, because the plant was moved, because the roots shrivelled and detached — the cytokinin signal drops. The auxin-dominated juvenile programme reasserts itself. The next leaves come out smaller and less divided. The plant is still there; it has just been told, by its own root system, that the climbing situation is over.

People sometimes notice this after repotting, after a very dry spell, or after moving a plant to a new location where the aerial roots need time to reattach. It tends to reverse within two to four growth cycles once contact is restored, which can feel slow — but is actually fast, given that the plant is reorganising its hormone balance.

The leaf you get is the leaf you earned

There is something I find genuinely satisfying about this. The giant fenestrated monstera leaf that has become such a design icon is not an accident of good lighting or a houseplant lottery. It is evidence of a relationship between the plant and its support. The leaf got bigger because the roots found something to hold onto. The holes appeared because the hormones said it was time.

Give the plant something rough and moist to climb, keep the roots in contact, and the rest follows.